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Reprinted from the September, 1967 Issue of WATER AND WASTES ENGINEERING Copyright 1967 by The Reuben H. Donnelley Corporation WASTEWATER SYSTEMS pipes and piping water and wastes / engineering / MANUAL OF PRACTICE NUMBER THREE PART 1/SYSTEM DESIGN PART 2/MATERIALS PART 3/INSTALLATION PRACTICES PART 4/MAINTENANCE CTD014819 BY GEORGE E. SYMONS, PH.D. EDITOR, WATER AND WASTES ENGINEERING PUBLISHED BY THE REUBEN H. DONNELLEY CORPORATION, NEW YORK, N. Y. SEPTEMBER 1967 | M 1 CONTENTS PART 1/SYSTEM DESIGN ....................................................M3 Introduction ........................................................................M3 Section 1--Sewer system types.........................................M3 Section 2--Preliminary considerations........................... M4 Preliminary report.......................................................... M4 Engineering report.......................................................... M4 Section 3--Sanitary sewers............................................... M5 Location ..........................................................................M5 Capacity ..........................................................................M6 Section 4--Hydraulics of sewers.................................... M10 Flow in pipes.................................................................Mil Flow formulas ...............................................................Mil Pipe flow chart...............................................................M12 Minor head losses........................................................ M14 Section 5--Storm and combined systems.....................M16 Planning ........................................................................M17 Location and drainage areas.......................................M17 Capacity ........................................................................M17 Combined sewers ........................................................ M17 Section 6--Appurtenances ............................................. M18 Types of appurtenances ............................................. M18 Section 7--Inplant systems............................................. M21 Design ............................................................................M21 Layout and arrangement............................................. M21 PART 2/PIPE MATERIALS ................................................. M21 Section 1--Selection criteria...........................................M21 Section 2--Design factors............................................... M22 Trench loads .................................................................M22 Embankment loads ...................................................... M23 Supporting strength ....................................................M23 Section 3--Asbestos-cement pipe.................................. M24 Pipe characteristics...................................................... M24 Linings....................................... M24 Joints and fittings........................................................ M24 Specifications ...............................................................M24 Manufacturers...............................................................M24 Section 4--Bituminized Fiber......................................... M25 Manufacture ................................................................. M25 Testing............................................................................ M25 Surface characteristics ................................................M26 Joints ............................................................................ M26 Commercially available pipe.......................................M26 Manufacturers............................................................... M26 Section 5--Brick and clay blocks.................................. M26 Section 6--Cast iron pipe............................................... M27 Section 7--Clay pipe........................................................ M27 Design ......................................................................M27 Pipe characteristics...................................................... M28 Manufacture ................................................................. M29 Manufacturers...............................................................M29 Section 8--Concrete pipe............................................... M29 Design............................................................................ M30 Characteristics............................................ FOREWORD this manual of practice, the third in a projected series to be published by water and wastes engineering, is devot ed to pipes and piping systems used in wastewater disposal operations. This manual is a sequel to Manual of Practice No. 2, which covered pipes and piping systems in water supply op M2 I WATER AND WASTES ENGINEERING Manufacture ................................................................. M32 Testing............................................................................ M33 Liners and lining...........................................................M33 Joints and fittings........................................................ M34 Cast-in-place concrete..................................................M34 Manufacturers ...............................................................M34 Section 9--Plastic and plastic lined pipe..................... M34 ABS, PE, and PVC pipe............................................... M34 Styrene-rubber plastic pipe.........................................M34 Truss-type plastic pipe................................................. M35 Manufacturers ...............................................................M35 Section 10--Reinforced resin pipe...............................M36 Reinforced epoxy or polyester plastic....................... M36 Reinforced plastic mortar...........................................M36 Manufacturers.............................................................. M37 Section 11--Steel pipe.................................................. M37 . Smooth wall steel pipe.. M37 Pressure sewer pipe .... ................................. M37 Corrugated steel pipe ................................................ M38 Manufacturers ...............................................................M40 Section 12--Wrought Iron pipe.................................... M40 Design and manufacture............................................. M40 Characteristics...............................................................M40 Manufacturers...............................................................M40 Section 13--Pipe lining in the field..............................M40 Cement-mortar lining.................................................... M40 Epoxy linings.................................................................M41 Other lining materials..................................................M41 Manufacturers...............................................................M41 Section 14--Inplant piping systems..............................M41 PART 3/INSTALLATION PRACTICES ................................M42 Section 1--Trenching practice.......................................M42 Excavation......................................................................M42 Sheeting and bracing..................................................M42 Dewatering ................................................................... M42 Section 2--Pipe installation........................................... M42 Pipe handling . . .................. M42 Bedding.......................................................................... M42 Pipe placement.............................................................M43 Pipe grade and line...................................................... M43 Jointing procedures...................................................... M43 Inspection and testing................................................. M46 Backfilling ..................................................................... M47 Section 3--House sewers and inplant systems............M47 House sewers ...............................................................M47 Inplant systems............................................................ M47 PART 4/MAINTENANCE ............. M48 Section 1--Collection systems...................................... M48 Extent of problems......................................................M48 Inspection policy.......................................................... M48 Cleaning sewers .......................................................... M48 Storm sewer .................................................................M49 Force mains .................................................................M49 Appurtenances.............................................................. M50 Outfalls ..........................................................................M50 Section 2--Repair............................................................ M50 Lining-in-place...............................................................M50 M31 Manufacturers ...............................................................M50 erations. The purpose of these manuals is to provide ready, concise, and basic information. Manual of Practice No. 3 is particularly intended for persons interested or involved in the design, management, supervision, operation, and main tenance of municipal or industrial wastewater disposal sys tems. CTD014820 PART 1/SYSTEM DESIfiN Introduction piping systems in wastewater disposal, commonly called sewers, have two basic functions: to collect and to transport domestic sewage and/or industrial wastes. Throughout this manual, the term sewer will refer to collection systems that transport wastewater from point of origin to point of treat ment or ultimate disposal. Sewers and piping that operate under pressure are gener ally termed force mains. The term inplant piping is com monly applied to piping systems within a treatment plant, regardless of the system's particular use. According to Babbitt,1 there is archeological evidence of sewers in Nippur, India (3750 BC) and Bagdad (2500 BC). The Cloaca Maxima, an arched sewer constructed in the 1 st century AD to drain the Roman Forum, is still in ex istence. Modern sewer systems date from the early 19th century. Table 1 briefly traces the history of sewer systems. The importance of sewer systems in the United States is indicated by the fact that, in spite of the large number of communities already sewered, the money currently being spent for sewer systems is approximately 62 percent of the total annual put-in-place construction cost for wastewater disposal facilities. Unlike water mains, sewers seldom contain valves, except overflow gates, but do have a number of appurtenances, in cluding: catch basins, flow measuring devices, flushing sys tems, inlets, junction chambers, lift stations, manholes, overflows, regulators, siphons, ventilators, and weirs. Sewers contain no moving parts and therefore operation, so-called, is largely a matter of cleaning and maintenance. The principal role of sewers is to provide a water-tight pas sage through which wastewater can be transported quickly, with a minimum of decomposition and without odor pro duction, stoppage, or overflow. If the transportation of wastewater through a sewer is dis rupted or impeded, problems may occur in treatment plant operations. It is important, therefore, for operating person nel in wastewater treatment plants to understand the most common sewer problems: exfiltration, grease, grit, or trash accumulation, infiltration, organic matter decomposition, root penetration, solids stranding, unevenness of sewer grades, and potential danger from flammable liquids. Insofar as possible, within the available space, this man ual will deal with different types of sewers, their design, ma terials used for construction, installation procedures, appur tenances, and maintenance. Section 1--Sewer System Types Sewers and sewer systems may be classified in four ways, according to: character of wastewater carried, relative posi tion in the system (or service), design configuration, and materials of construction. Tables 2 and 3 show the basis of classification of the dif ferent types of sewers in each of the first two categories. Sewers may be classified according to the design configu ration: barrel, basket-handle, catenary, circular, egg-shaped, horseshoe, ovoid, rectangular, or semi-elliptical. Classification of sewers is also based on the material of construction (see Part 2). BY GEORGE E SYMONS, Ph D. Dr. Symons is editor of V \TLR and wastes engineering. He is a Diplo- of American Academy of Environmental Engineers; a Fellow ovf?2AeSrCaTE and APHA; Life Member .^lember of tVPCF, and a and Fuller Awardee of member of ACS, AICHE, AWWA; AIDIS, an and NSPE. Author of numerous articles on water supply and wastewater dis- posal. he was editor of 29 design criteria manuals for the Engineering Facilities Command. U. S. Naw, and author and editor of two operation and maintenance manuals for the EFC of the V. S. Navy, one on water supply and one on wastew-ater disposal. TABLE 1--HISTORICAL DEVELOPMENTS IN SEWER IYSTEMI Approi. yar Event 1803 1805 1815 1833 1843 1857-58 1880 1915 1952 Concrete sewer installed In New London, Conn. New York City's first large sewer installed Excreta admitted to London sewers Construction of Paris sewers begun First full-scale sewer system for sanitary sewage Installed in Hamburg, Germany* Sewer systems designed for Brooklyn (N.Y.)and Chicago Separate sewer system installed in Mem phis, Tenn.* Last comprehensive sewer system for a large city completed in Baltimore 11,420 municipal sewer systems in United States reported by U. S. Public Health Service' TAKE !--CLASSIFICATION OF SEWER IT TYPE OF WASTE 0ARRIED Type of fewer Character of wastewater carried Sanitary Storm Combined Separate Industrial wastes Cooling water Domestic or sanitary sewage from house holds, commercial buildings, or indus trial establishments Storm water runoff from streets and land Both sanitary sewage and storm water Either storm water or sewage and indus trial wastes, but not both Wastewater from wet manufacturing or process Industries; sanitary sewage may or may not be Included Water used for cooling purposes and discharged essentially unaffected bv use CTD014821 TABLE S--CLASSIFICATION OF SEWEi. pi LOCATION IN SYSTEM 0B PURPOSE Type at aawar Location In ayatnm or purpoao House Lateral Branch Main (also called trunk) Relief Interceptor Force main Influent Outfall (also called effluent sewer) Receives household wastes from building plumbing drainage system and carries them to the street sewer Carries wastewater into another sewer (branch); has no other common sewer tributary to it Receives wastewater from laterals and carries it to a main or trunk sewer Receives wastewater from many trib utary branches or laterals; serves a large area Receives flow (overflow) above the capacity'of an existing sewer Receives dry-weather flow, and often storm water up to 5 X DWF, from a number of transverse (main or trunk) sewers. Interceptors are usually large, flew parallel to a natural drainage channel, and dis charge to a treatment plant or to a receiving body of water A sewer through which wastewater (or sludge) is pumped under pressure from one level to a higher level or from one plant to another Sewer or interceptor leading into a treatment plant Sewer or pipe leading from an inter ceptor or treatment plant to or into a receiving body of water SEPTEMBER 1967 ! M 3 Section 2--Preliminaiy Considerations in Design Except in small uDsewered communities, the need to de sign a complete municipal sewer system has rarely arisen in the last 50 years. (There are exceptions, however, where new communities have been built, e.g., Levittown, L.I., Levittown, Pa., and Foster City, Calif.) Most sewer design projects today pertain to the sewering of newly developed residential areas within a city, construction of intercepting and/or storm sewers, separation of sanitary and storm sew ers, replacement of undersized, overloaded, or collapsed sewers, and construction of sewers for the transportation of municipal and/or industrial wastes to wastewater treatment plants. Preliminary report Many municipalities have sewer departments employing engineering staffs to design necessary sewer systems; other communities utilize the services of consulting engineers. In both cases, the designer must make a number of decisions and carry out several operations before the final engineer ing design can be undertaken and construction begun. Gen erally a preliminary engineering report on a proposed sewer system reviews the needs of the community, estimated cost, financing methods, means for obtaining public support, and pertinent ordinances. Engineering report Once the preliminary report has been accepted and ap proved and arrangements or contracts have been made for the work to proceed, a full scale engineering report expand FINANC1NO METHODS ing on all phases of the preliminary report is usually pre The engineering report should contain an evaluation of pared. and actual design begins. Sometimes, only the de the possible methods of financing, with recommendations as tailed engineering report and plans are prepared. Among to the preferable method. The common methods to be eval the more important items included are layout, cost esti uated are: mates, financing methods, sewer ordinances, and public relations efforts. General obligation bonds General taxation Sewer service charges Special industrial waste LAYOUT The basic map of the area to be sewered should show locations of pertinent existing buildings, utilities, and drains. The basic map and engineering data should also include the Government grants and loans Private capital Revenue bonds charges Combinations of the above methods following information: System layout for the entire tributary area, with route al ternatives, if necessary; Estimated future growth of the area; The choice of financing methods often depends on the local situation, and each method has its proponents. With the passage of PL 89-234, The Water Quality Act of 1965, and of PL 89-753, The Clean Waters Restoration Act of Estimated current and future flows from tributary areas; Indicated pipe sizes, elevations, and grades; 1966, the use of federal grants and funds has become one of the most important methods of financing sewer facilities. Topographic contour lines; Modern practice also favors the use of sewer service Preferable materials of construction. charges and special charges to industry for treating indus A concise review of the method of developing a sewer sys tem layout has been published by the National Clay Pipe trial wastes. Special industrial waste charges were proposed more than 40 years ago, but the first such industrial waste Institute.4 Figure 1 shows a typical layout map for sewers.4 charge formula was developed and instituted by Symons COST ESTIMATES and Crane in Buffalo in 1943.8 A number of different for mulas have since been used elsewhere. A definitive review Babbitt and Baumann3 recommend that the engineer's es of the most important formulas was published in 1954.7 timates of costs be grouped and divided among the follow ing categories: SEWER ORDINANCES Labor Materials Overhead Contingencies Profit Engineering and Legal expense Where municipal ordinances do not provide adequate Landacquisitcioonntrol of the wastes discharged into sewer systems, it is Extra work often desirable that the engineering report cover this matter Inspection and include basic recommendations for development of In addition to the above categories, these authors5 suggest that estimates of sewer costs be stated on a perlinear-foot basis, with the following detailed items: adequate ordinances. A guide to the development of sound municipal sewer or dinances is contained in WPCF Manual of Practice No. 3, "Municipal Sewer Ordinances."8 Excavation, rock (per cu yd) Repaving Excavation, earth (per cu yd) Flushing systems PUBLIC RELATIONS Backfill (per cu yd) Special sections In any effort to obtain public support for financing sewer Manholes Testing construction projects, both the engineers and municipal Catch basins officials must make full use of all means of informing the M 4 I WATER AND WASTES ENGINEERING CTD014822 Asbestos-cement sewer pipe laid in trench that nefeded no sheeting. public. These efforts will include newspaper, radio, and television publicity, talks before service clubs, etc. Materials to aid a community in its public relations ef forts are available from a number of sources. The Water Pollution Control Federation has published several relevant pamphlets, including one titled, "Public Relations for Water Pollution Control;" other pamphlets and bulletins are avail able from federal government agencies. Films for public showing have been prepared by many manufacturers. A book by M. M. Cohn,2 contains information and sugges tions for public relations projects related to sewers. Some manufacturers' associations and companies have published guides on community relations with respect to water supply systems. The principles in these bulletins are also applicable to sewer system projects. Section 3--Sanitary Sewers The design of a sewer system depends on several factors, including type (sanitary, storm, or combined sewer), loca tion. capacity required, grade, depth, and trench load. Generally sanitary sewers are more desirable than com bined sewers and should be installed when the following sit uations exist:1" Sanitary sewage collection needs are immediate, but storm flow collection needs are not immediate; Conditions favor overground transmission of storm wa ters for long distances; Disposal of combined flow would require pumping, but storm flow pumping would not be necessary; Treatment of storm waters is not necessary. When the capacity of an existing system is sufficient for sanitary sewage flow but not storm water, a separate storm sewer should be constructed. Combined sewers should be installed only when an eval uation of the above factors indicates that a combined sys tem is more applicable than separate systems. Many states require plans for sewer systems to be ap proved by the state health department before the start of construction. These plans should include:9 General map of municipality or sewer district, with drainage areas and location of sewers and appurtenances shown in detail; Detailed plans and profiles of sewers; Details of appurtenances; Comprehensive report on proposed system; Specifications. Location In locating sewers, the following factors should be con sidered: costs, grade, soil conditions, safety during con struction, future expansion, etc. The best route may not necessarily be the shortest one. GENERAL CONSIDERATIONS The sewer route chosen determines the layout, which should be shown in the layout map (Fig. 1). This map should contain present and future street locations; contour lines of the area (at the smallest feasible intervals); present, currently proposed, and future sewers; elevations, sizes, and grades of sewer lines. Generally, sewers should be laid in the streets, or in alleys between property lines, but not, for several reasons, on ease ments on property. Location in grassy areas in or along wide streets or boulevards is desirable to avoid disturbing the pavement. Sewers should usually be laid in straight lines, particularly between manholes; in housing developments where streets are curved, the sewer line will usually curve accordingly. Curved sewers with radii of 100 ft or more have generally given satisfactory service. Wherever possible, lateral sewers should be laid within 50 ft of every lot or should provide for the shortest possible house connections; the location should also provide for proper cellar drainage of all property, without pumping. A manual published by The American Society of Civil Engineers11 provides a standard practice for locating sani tary and storm sewers. The sewer system layout will generally fit into one of two classifications: perpendicular or fan-shaped. Where the to pography of a community is characterized by different lev els, or by ridges and valleys, the sewer system layout may involve combinations of perpendicular and fan configura tions, with or without lift stations and interceptors. PROCEDURAL STEPS One reference work4 suggests the following steps in de veloping the layout of a new or expanded sewer system. Trunk sewers. Begin at the point of discharge or outlet of the trunk sewer (i.e., at the lowest elevation) for the area under consideration and work uphill along the route of min imum slope. The line must eventually reach the edge of the drainage area or ridge line between drainage areas. Location map. Revise the tentative layout to produce the shortest possible route. If possible, avoid layouts that re quire a sewer slope opposite to the ground surface slope. The final trunk line location should have a minimum length, require a minimum amount of excavation, and pro vide for drainage downward from both sides of the line for the entire area. Branch sewers. Follow the same basic procedure as for trunk sewers, making each branch provide complete drain age of its own subdrainage area using the shortest possible length and minimum excavation. Laterals. Locate the laterals from branch sewers in streets, using the same principles and procedures as for trunk sewers, i.e., minimum excavation and length, complete ser vice to area, etc. CTD014823 SEPTEMBER 1967 | Ml 5 Service areas. Add to the location map the division lines that show the areas served by each trunk sewer, branch, or lateral. Each district should consist of all the acreage within which the flow is toward the point where the sewer crosses the boundary line of the area. Sub-areas on laterals should generally be no more than two blocks long. Tributary load. After completion of the area location map, the acreage and expected tributary flow for each area should be calculated and tabulated in a cumulative manner that will show, at any particular point on the sewer, the sewer length, acreage, and flow tributary to the point. Capacity The required sewer size (diameter) depends on the vol ume of wastes to be handled in a period of time and on the hydraulic characteristics (grade,-etc.) of the sewer. The volume of flow to be handled depends on population tributary, waste discharge per capita, amount of water en tering the sewer from the soil outside (infiltration) and the leakage from the sewer (exfiltration). It is difficult and expensive to expand or increase the ca pacity of a sewer system once it is installed. There are only two means for doing so: digging up the sewer and replacing it with a larger size, or installing a parallel system. Both methods are costly. Therefore, it is good practice to make predictions of future population and flow on the best pos sible basis. Unfortunately, even the best estimates may be in error. POPULATION TRIBUTARY The prediction of population trends is complicated by a variety of technical, physical, social, political, economic, and other factors, including the strong trend to urbanization in this country. Prediction methods. The designer must choose the best possible method and use his judgment in arriving at the most likely future population. Two groups of methods are available: mathematical and logical. Mathematical methods. These methods include arithmeti cal and geometrical progression, decreasing rate of increase, and differential plot. All are subject to criticism for failure to give more than a poor guess. The mathematical approach is based on the assumption that a city, or area, in its early or "young" stages will increase in population geometrically, possibly by some fixed percentage for each interval of time; that later, for a certain time interval, the population will in crease at a more or less uniform rate (i.e., by some fixed number for each time interval), and that, eventually, the rate of increase will taper off until some limit is reached, after which there will be no further increase. The problem is to determine which stage currently exists, and the percent age or fixed-number increase to be used. Population trends since 1950 have changed considerably because community growth has been influenced by local conditions, such as de velopment of industry, transportation, changes in popula tion age distribution, and other social and political trends. The mathematical approach is more unreliable today than in the years before 1940. Mathematical methods also include the graphical exten sion of plotted data, graphical comparison with other cities, and application of the Verhulst theory. Graphical extension of plotted data or graphical comparisons with other cities involve the plotting of census data against time. Figure 2 shows the plotting of population records of the United States and several states and cities to 1950. Current growth patterns are different from those before 1950. Graphical comparisons with other cities will only be as good as the designer's judgment in interpreting the plots. This judgment must include consideration of all of the fac tors mentioned above. The Verhulst theory utilizes the principle that the popula tion in any area increases only to a saturation limit.12 M 6 I WATER AND WASTES ENGINEERING Fig. 2. Population trends in the United States. Logical methods. These methods include the component method, the cohort survival method, and the ratio method. The first method involves the use of birth and death rates and expected future migration trends. The second method involves the computation of data on each age group for the entire projection period. The ratio method consists of three steps: determination of the ratio, of the population in the area under study to the population of a larger area; extrapo lation of that ratio to the terminal year of the prediction period; and conversion of the extrapolated ratio back to the predicted population for the smaller area. Prediction period. The period for which a population prediction applicable to main sewers and interceptors is to be made should be selected according to the local situation. It may be as short as 10 years or as long as 50 years. The selection of the period will be affected by many factors, such as legal limits on bond issues, economy, available funds, predicted population level, and the relative impor tance assigned to each factor by the designer. Bond issues frequently have a life span of only 20 to 30 years, but it is often desirable to predict population growth for longer pe riods. Some compromise between the bond life and the long er period desired may be the best solution so that the suc ceeding generation is not burdened with the cost of fa cilities for current use. Population predictions to be used in the design of lateral sewers should be based on full develop ment of the area served and not on any specific length of time. Population data sources. Information on population trends may be obtained from the U. S. Bureau of Census, the Population Reference Bureau in Washington. D. C., and state and regional agencies. Local telephone and power companies usually have excellent data on local area growth. FLOW CAPACITY The estimation of the volume of liquid to be carried in a sewer system and the selection of the necessary pipe size CTD014824 Large diameter piastic pipe entering manhole location. must take into account the current tributary domestic, in dustrial, and commercial waste load, infiltration, and exfil tration. In making estimates of flow, many factors must be considered, the most important of which are discussed below: Flow rates. For the design of sewer systems, it is neces sary to know the total amount of liquid to be handled dur ing various periods of time and, also, different instan taneous rates of flow. Inasmuch as sewage flows more or less continuously, any expression of amount is meaningless unless the time period involved is known. The amounts of wastewater may be expressed in terms of rate of flow or discharge per unit time. The total volume for any day is the average of the variable instantaneous rates of flow throughout a particular day. It need not be confusing to express both total flow and in stantaneous flow rates in the same terms (gpd or mgd). In fact, it is convenient to do so when making future predic tions or estimates. Flow data expressed in gallons per day may be converted easily to data expressed as cubic feet per second for use in standard hydraulic formulas, or as gallons per minute for use with printed charts or graphs. Flow data may also be expressed in terms of gallons per capita per day. In this way, flows from different areas or cities may be compared. Flow data expressed as gallons per capita per day are often used as the basis for making future quantitative estimates. Per capita flow data may also be use ful for other predictions. The term "per capita" does not have a single meaning. For example, the per capita flow for an entire city may be the total flow divided by the total population, or it may be the total flow divided by the sewer-connected population. The two may be quite different. Also, the sewage flow for business, commercial, and industrial discharges may be re ported on a per capita basis, and the value may be deter mined on four different bases. The total flow may be divid ed by: (1) total number of persons in the city; (2) the sewer-connected population; (3) the number of persons re siding within the business, commercial, or industrial area under study; or (4) the number of persons working within the area under study. The values will differ markedly. Generally the choice of method for determining per capi ta flows is immaterial, providing it is stated and understood. However, when the total per capita flow for a community is computed by adding the per capita flows for domestic, busi ness, commercial, and industrial areas, then it is important to use the same basis for calculating each category. Ductile iron 24-in. force main at Creve Couer, Mo. CTD014825 Average flows. The total sewage quantity consists of the individual flows from the various area categories (residen tial, business, commercial, and industrial). This total flow will bear some relation to the public water supply use of the community, but this relation varies from city to city, de pending on the amount of unaccounted-for water, the amount of water used for public purposes and for lawn sprinkling, the number of individual water supply wells in the community, infiltration and exfiltration in the sewers, and the extent to which storm water and roof drainage is kept out of the sewers. Where good estimates of these various factors are not available, actual measurement of the flow in sewers is the TMLE 4-WATEi USE AND SEWAGE FLOW IN VARIOUS CITIES City Akron, Ohio Ann Arbor, Mjch. Auburn, N. Y. Aurora, III. Buffalo. N. Y. Av*ra quantity (aped) Water* Sewage 121 190 116 110 187 136 81 132 202 242 Cleveland, Ohio Detroit, Mich. Fitchburg, Mass. Galesburg, III. Gary, Ind. 165 130 141 141 183 82 96 159 98 195 Green Bay, Wis. Indianapolis, Ind. Kenosha, Wis. Marion, Ind. Marshalltown, Iowa 83 188 109 147 141 205 139 153 112 170 Minneapolis, Minn. Niagara Falls, N. Y. Oshkosh, Wis. Pasadena, Calif. Phoenix, Ariz. 93 141 394 670 64 125 150 70 253 142 Racine, Wis. Rochester. N. Y. Toledo, Ohio Urbana, III. Washington. D. C. 174 202 118 134 147 126 87 93 165 147 Worcester, Mass. 103 138 * From "A Survey of Operating Oata for Water Works m 1945" AWWA*0: 165(1948). ** From operator's reports, mostly 1945, others between 1943 and 1947. SEPTEMBER 1967 I M 7 best method of obtaining the desired data. The wide varia: tion between water use and wastewater flow in a number of cities is shown in Table 4. Although these data were collect ed some time ago, they indicate the possible variations be tween water supply quantities and wastewater flow. Water use records of a number of metered water supplies plus careful sewer gagings indicate that the average domes tic sewage flow may vary from 15 to 70 gpcd, depending on type of dwelling and economic level of people served. For example, the following rates may apply in communities where the water service is completely metered: Dwelling type Apartment house First class Middle class Lower class Flow (gpcd) 65 55 40 25 Where water supply charges are based on flat rates, flow values will be higher, and, in the lowest class dwellings, may be twice the above figure. For design purposes, it is advis able to select a value of 50 gpcd or more for calculations of domestic sanitary sewage flow. Waste flow from business and commercial districts is generally related to the amount of contributing floor space; a common estimate is 300 gpd per 1000 sq ft of floor area. Industrial wastes vary widely in volume depending on the type of industry, inplant treatment or disposal, and the use of cooling water. Only a careful study of industrial sewer gaging can indicate the extent of the industrial load. When selecting the estimated flow rate values to be used for design purposes, it must be remembered that the esti mate is for future conditions and that the per capita average flow is more likely to increase than to decrease. One simple means of estimating sewage flow rates, often used for preliminary estimates, can be illustrated by the fol lowing hypothetical example: Item Domestic sewage Business and com mercial wastes Industrial wastes Infiltration Total avg. flow Calculation 100 gpcd x 12,000 pop. 10,000 gpcd X 64 acres By measurement 5000 gpd/mile X 23 miles Flow rate (mgd) 1.2 0.64 0.27 0.11 2.02 Infiltration and exfiltration. Ground water may leak into a sewer (infiltration) or wastewater may leak out of a sewer (exfiltration). Such leakage may occur through poor joints or cracks in the pipe or manholes, which may result from poor construction, settlement after construction, or deterio ration of materials. Most of the time, a sewer pipe carries only a portion of its maximum capacity, and the tendency for water to leak out is small. On the other hand, the ground water level, ei ther normally or after rains, may be well above the top of the sewer, and an appreciable amount of water may enter the sewer. Both modern pipe and modern joints have con tributed greatly to eliminating or minimizing infiltration. Ex traneous water in sewers is likely to come from illegal con nections from roof drainage, surface runoff through man hole covers, and forgotten or unrecorded street inlets. The resulting infiltration may be expressed in gallons per day per acre of area served, in gallons per day per mile of sewer line, or in gallons per day per inch diameter per mile of sewer. The last method is the most logical, and a com mon value for design purposes is 200 gpd per in. diam. per M 8 I WATER AND WASTES ENGINEERING Fig. 3. Hourly sewage flows in two Buffalo, N. Y., sewers. Fig. 4. Variations in daily and hourly flow in Albany St. sewer, Buffalo, N. Y.; tributary population--33,000. CTD014826 12 5 10 20 POPULATION (THOUSANDS) 50 100 Fig. 5. Extreme flow rates as a function of population.' '* mile. However, when making estimates for design purposes, the sewer size is not known, so other values may be used: 5000 gpd per mile, or 200 gpd per acre. Extreme condi tions may halve or double these values. The prediction of infiltration rates may also be expressed on a per capita basis, in which case values between 10 and 40 gpcd are often used. Infiltration rates vary, depending on sewer construction, type of soil, elevation of water table, manhole leakage, roof drainage, etc. (See discussion of flow variations.) When predicting extreme maximum rates of flow for design pur poses, it is usually desirable to consider infiltration rates separately. Relatively few data are available on measured rates; they indicate a wide range of values. Velzy and Sprague13 reported in 1955 on the infiltration specifications set by 11 consulting engineers and 13 cities. The ranges of these specifications are shown in Table 5. These specifications are outdated today for new sewer con struction because pipes and pipe joints have been greatly improved in the past 10 to 20 years. Current specifications TABLE 5--INFILTRATION SPECIFICATIONS" Allowable infiltration (gpd/mile) Per in. diam. Min. Max. 8-in pipe Min. Max. 24-in pipe Min. Max. Consulting engineers 175 875* 1400 7000 4200 21,000 Cities 145** 1500** 1160 12,000 3480 36,000 Some engineers used higher values for wet pervious ground and short sections. One city used 10,000 gpd per mile of pipe regardless of pipe size. should be much stricter. These data are included here for reference purposes only. Exfiltration is seldom considered in determining design capacity of sewers. It is a condition that is highly undesir able, and all efforts should be made in design and construc tion to prevent such leakage. Variations in flow rate. Average daily volumes or rates of flow, as discussed above, represent the average of all variations during the day. These variations range from a maximum during the morning hours to a minimum after midnight. Between these rates, the variation depends on the character of the community, its work habits, and other fac tors. Not only will flow rates vary throughout the day, but they will differ from day to day (see Figs. 3 and 4), and from season to season. It is obvious from the data in Table 4 and from Figs. 3 and 4 that the average flow varies widely, hence it is advis able to compare and predict data on a per capita basis. To make comparisons of variable rates of flow, it is common practice to compare the ratios of various flow rates to the average flow. Such a ratio may be used to compare any stated flows, such as maximum and minimum. Use of this ratio is of value not only in making comparisons, but also in predicting the magnitude of flows for design purposes. Extreme flow rates. The relation of extreme flow rates to the average flow is influenced by a number of factors, in cluding the character and work pattern of the neighbor hood. The smaller the area, the more pronounced is the change in the ratio of extremes to average flow (see Fig. 3). In other words, the ratio of extreme maximum flow to aver age flow is inversely proportional to the population served. Furthermore, the peak sewage flow will follow the peak water use load, and vice versa. Other water uses and wastewater sources have compen sating effects. Infiltration can vary with the season, as does CTD014827 SEPTEMBER 1967 ! M 9 0.1 1 10 Fig. 6. Extreme flow rate$ as a function of average flow.1* the amount of public water supply used for lawn sprinkling, etc. Both affect the ratio of maximum to average flow, but to some extent they are compensating factors. Extreme flow rates may be related either to population or to average flow rates. Figure 5 shows the recommended values of several authorities for extreme variations in sewage flow with respect to contributing population, and Fig. 6 shows comparable data on the basis of average flows. The equations for Fig. 5 are: Qmax. -- QtTf. Eq. 1 Qmln.=Q.v.X^ Eq.2 where: Q = flow rate (cfs) P = population (thousands) The equations for Fig. 6 are: Qmax. = 4 X Q-* Eq. 3 Qmta. = 0.25 X Q> 1 Eq. 4 These equations are empirical and are applicable only over a certain range. If the lines on the graphs were extend ed, maximum and minimum lines would intersect at some large population or large average flow rate. This is im possible, and these equations should therefore not be used for populations greater than 100,000 or average flows greater than 10 mgd. Patterns of flow rate variation for business, commercial, and industrial areas differ somewhat from pattern of varia tion of domestic sanitary sewage flow variations. The ratio of maximum or minimum to average flow rate is generally smaller than for domestic sewage. Some designers use a constant value based on total city population. Relating ex M 10 I WATER AND WASTES ENGINEERING treme flows to average flows, as in Fig. 6, is usually simpler and is satisfactory. SIZING SEWERS When the maximum flow rate has been determined and the ground surface profile has been established, the diame ter, slope, and depth of the sewer, and manhole elevations must be determined. The size and slope of a sewer depend on the maximum flow rate to be handled and on the hydraulics of wastewater flow. The subject of flow hydraulics and its importance in sewer design is discussed in Section 4. Section 4--Hydraulics of Sewers* In the design of a sewer system, the fundamentals of hy draulics are most important. As a basis for considering the hydraulics of sewers, the following principles apply: 4 Sewage has the same flow characteristics as water be cause its solids content is not high enough to appreciably change its specific gravity from that of water. The surface of flowing sewage will, under the influence of gravity, seek its own level in a sloping channel. This is termed gravity flow. Constant discharge from free flowing sewers is termed steady state flow, but under normal sewage flow conditions, steady state does not exist. Uniform flow in sewers requires successive sewer cross sections to be the same, and mean velocity, sewage volume, sewer slope, size, and alignment to be constant. * This section on hydraulics is largely a contribution of the late Professor H. M. Gifft of Cornell University. Much of it was taken from the unfinished manuscript of a text book on sanitary engineer ing jointly authored by H. M. Gifft and George E. Symons. The untimely death of Professor Gifft halted the writing of that text book when it was half finished. CTD014828 The flow in partly full sewers is characterized as open channel flow. Sewers flowing full under pressure (siphons, force mains, and overloaded sewers) are surcharged. Flow in pipes and conduits Wastewater flowing in either an open or closed conduit has energy of position and of motion. Under conditions of steady flow, the total energies at any two points along the path of flow will be the same, except for loss of energy re sulting from friction between the two points. In terms of difference in elevation, the principle, known as Bernoulli's theorem, is written as: V2 + H + : Z" + H" + VJk2 + Eq. 5 where: Z, and Z|, = elevation of invert above datum plane at points a and b H,and Hb = elevation of water surface above sewer invert at points a and b, or the hydraulic gradeline and ~ = elevation of energy gradeline above hy 2g 2g draulic gradeline at points a and b Hf elevation of energy gradeline at point a minus the elevation of the energy grade line at point b The explanation of these terms becomes apparent in Figs. 7 and 8. (Lin these figures is the distance between points a and b.) Under uniform flow conditions, the situation most often encountered in sewer systems, the velocity of flow is con stant between points a and b, and, therefore, the hydraulic gradient is parallel to the energy gradient and to the invert. Because the slopes are equal, the terms are sometimes used interchangeably: more often, however, the term hydraulic gradient is used, and the energy gradient is ignored or for gotten. For pipes flowing under pressure, the velocity head is quite small and. because it usually has a relatively constant value, may have little effect on the flow. There are times, however, when the value of the velocity head is a most im portant factor and cannot be ignored. In open channel flow, as in sewer pipes, the velocity head can often be ignored because it does not change appreciably from point to point. The magnitude of velocity head, how ever. often is appreciable with respect to depth of flow, and therefore, may have an influence in junction chambers, manholes, and at points of change in sewer size and direc tion. How formulas Computations for sewer design are generally made on the basis of the sewer flowing full but not surcharged. Flow for mulas have been developed for computing head losses re sulting from friction along a length of pipe or channel. One of the earliest formulas, developed by Chezy, is: V = C\/RS Eq. 6 where: V = velocity of flow (fps) S = slope of energy gradient or ratio of HF/L (see Figs. 7 and 8) R = hydraulic radius C = a coefficient In Eq. 6, S is only approximately equal to the slope (see Figs. 7 and 8); R, the hydraulic radius (expressed in feet), is the area of a cross section divided by the "wetted pe rimeter." The coefficient, C, was originally thought to be a constant, dependent only on the roughness of the internal pipe surface. Without delving into the relation of observed C values to Reynolds' numbers, it is sufficient to say that for normal conditions (Reynolds' numbers between 105 and 10T), the deviation of C from a constant value may not be too great. It is, however, large enough to have suggested a more prac tical formula in which the coefficient was more nearly a constant and dependent only on the roughness of the con duit surface. The most common method of improving the Chezy for mula has been to replace the Chezy "C" by another expres sion containing some term as a measure of surface rough ness. Kutter proposed for Chezy's C, the expression: 41.67 + (0.0028/S) + f 1.81 h) 1 + [41.6 + (0.0028/S)] [n/\/Rl where R and S are the same as in Eq. 6, and n is the suppos edly true roughness coefficient. Manning proposed another formula for Chezy's C: 1.486 ri c n Eq. 8 CTD014829 SEPTEMBER 1967 | Mil Fig. 9. Alignment chart for Manning's formula and Hanzen-William's formula for circular pipes flowing full. where n is intended to be the same as in Kutter's formula. Hazen and Williams also proposed an equation as a mea sure of surface roughness, Chezy's C. Hazen and Williams' C value has become the standard determination for comparing the roughness coefficient of pipelines in water systems; their formula is usually written as V = 1.318 x C X R"3 X S-M Eq.9 In the field of wastewater piping (sewers), either the Kutter or the Manning formula is used. The latter is the more com mon and is usually written as V _ E486 K- 3 St 2 n Eq. 10 Pipe flow chart The Manning formula conforms to the fundamental laws of fluid flow in relatively rough pipes, and the Hazen-Williams formula is reasonably close for "smooth" pipes. Fig ure 9 is an alignment chart for the Manning and HazenWilliams formulas. The relationship between n and C was determined by constructing the "hydraulic slope" scale so that the lines for n and C were coincidental.* The chart, therefore, is applicable in the solution of a number of equa tions of the form. Q = AV = KD> S' Eq. 11 M 12 ! WATER AND WASTES ENGINEERING where: Q -- flow (cfs) A = area of cross section (sq ft) V = velocity (fps) K = coefficient of roughness x = coefficient varying from 0.67 to 0.63 y = coefficient varying from 0.50 to 0.54 The use of the chart is similar to that for standard pivottype alignment charts except that the location of the pivot line is dependent on the roughness factor. Three of the five variables must be known, or assumed, and the other two may be found with a straightedge by one alignment and one pivot. Simultaneous values are always read on the same side of the pivot line. Examples. A 10-in. diam. pipe is to carry a flow of 5 cfs; line is dependent on the roughness factor. Three of the five C = 90. If a straightedge is lined between 10 on the diame ter scale and 5.0 on the discharge scale, the resulting velocity is 9.5 fps. To find the hydraulic slope, the straightedge is pivoted about the intersection with the pivot line labeled 90 to the mark 90 on the roughness scale. The resulting inter section in the hydraulic slope scale is 0.080 ft per ft. (Note: if the 150 pivot line had been used, the slope would have been incorrectly indicated to be 0.055 ft per ft.) * Another approach to the correlation between Manning's "a" and Hazen and Williams' "C" values is described by R. G. Dittig on p. 100 of this issue. CTD014830 A sewer pipe to be laid on a slope of 0.001 ft per ft is to carry a flow of 22.0 cfs; n = 0.013. A straightedge is lined between S = 0.001 and n = 0.013 to locate the point on the 0.013 pivot line. The straightedge is then pivoted about this point to Q = 22.0 and indicates the required diameter to be 36 in. and the velocity of 3.1 fps. SEWER DESIGN SLIDE RULE Another method of solving sewer design problems is to use a sewer design slide rule (see Fig. 10). This slide rule* has a wide range, is simple to operate, and is accurate. The device is based on the Chezy formula (V = C\/RS) with (Cutter's formula being used to determine the value of C. The slide rule includes scales for the following Scale Q % full L H V n D T Range 0.25 to 3000 cfs 10 to 100 10 to 3000 ft 0.1 to 40 ft 0.5 to 50 fps 0.011,0.013,0.015, 0.021 <6 to 216 in. 0.1 to 10 min VALUES OF C AND N Hazen-Williams C values to indicate roughness coeffi cient are not the same as Chezy's values, which are seldom used today. Both (Cutter's and Manning's formulas are in fairly common use, and both use an n value. For pipe di ameters smaller than 3 ft, there are considerable discrepan cies between the value of n in the two formulas. For pipe di ameters larger than 3.0 ft, the values of n are practically the same for both formulas. Many engineers prefer to use the Manning formula for solving pipe flow problems. A formu la developed by Scobey is often used for concrete pipe. Table 6 shows Hazen-Williams C values and Manning's n values for various pipe materials. The C-values are the same as thOse given in Manual of Practice No. 2;24 the n values given as ranges are the values recommended for de sign purposes by ASEC-WPCF Manual of Practice No. 9,24 which does not cover a number of pipe materials listed in Table 6. It should be noted that tests on most of these * Copyrighted 1947, by Irving Goldfein; U.S. patent no. 2,454,157. It is available from some pipe manufacturers or may be purchased from the designer. TAKE ft--HAZEN-WILLIAMS' 0 AND MANNING'S N VALUES* (For rariots pipe au(trials) Pipe material Asbestos-cement Bituminlzed fiber Brick Cast iron New Cement lined Old, tuberculated Clay Concrete (quality pipe) Fiberglas reinforced resin Plastic and truss type plastic Steel (pressure pipe) Corrugated steel Unpaved Coated and 1/4 paved Smooth lining Wrought Iron C value 140+ 140+ 140+ 80-100 140+ 140+ 140+ 140+ 140+ n valu** 0.011-0.015 0.013-0.017 0.011-0.015 0.011-0.015 0.015-0.035 0.011-0.015 0.011-0.015 0.024-0.026 0.021-0.023 0.011-0.015 ... C-valuas are those given in Manual of Practice No. 2` for water pipe and n-values are those given by WPCF Manual of Practice No. 9" (in revision), except as noted. .. ** The higher values ere used for wastewater where quality of joint construction is poor, where settlement may occur, or where the con struction is old; the lower values may be used for clear water. Values supplied by materials manufacturers are less than those shown. Where no n values are shown, values stated by manufacturers are also less than any value shown in this table. CTD014831 SEPTEMBER 1967 | M13 Fig. 11. Energy and hydraulic gradelines with respect to sewer elevations. pipe materials indicate an n value of 0.010 or 0.011, and many design engineers use these lower values in preference to those listed in Table 6, except where state regulations do not allow the lower value. Minor head losses Although friction between the liquid and the pipe surface may account for most of the energy or head lost, other loss es may also have to be considered. The estimation of minor losses in sewer lines is more difficult than in water pipelines, because the flow is not under pressure and the conversion back and forth between potential and kinetic energy (i.e., pressure head *=a velocity head) is less predictable. Further more, the change in elevation of the hydraulic gradeline owing to changes in velocity must also be taken into ac count because the crown of the sewer and the hydraulic gradeline are usually coincidental. , In general, the energy or head losses may be considered to be a function of the velocity above the point in question. That is Eq. 12 where: Hl = head loss (ft) V = velocity (fps) g = gravity constant (32.2 fps2) K = constant In addition, the change in hydraulic gradeline elevation is a function of the change in velocity at that point: _ V,2 - V,2 * 2g Eq. 13 The value of K in Eq. 12 depends on the cause of the head loss; it may vary from 0.1 to 2.0 but is usually less than 1.0. When the velocity is reduced, that is, when the sewer slope and the hydraulic gradient become less steep, an in crease in elevation of the water surface occurs. Because of open channel conditions, it is likely that very little of the velocity head will be recovered; it is therefore customary to assume that there will be no increase in elevation of hydrau M 14 I WATER AND WASTES ENGINEERING lic gradient at such points. Figure 11 is an illustration of the relationship between the energy and hydraulic gradelines with respect to sewer pipe elevations. PARTIALLY FULL SECTIONS The hydraulic values for a conduit flowing less than full may be calculated by the usual formulas, but the computa tions are laborious. A simpler method is to use special di agrams. Figure 12 is a diagram for the solution of such problems in connection with circular sections. The use of this chart is relatively simple for the solution of problems in terms of the relative values of the several variables. In Fig. 12, the values of the variables are shown in terms of full-flow conditions. As can be seen from Fig. 12, it is possible for sewers to carry liquid at a higher rate when flowing partly full then when flowing full. In the design of sewers, it is not desirable to rely on this apparent anomaly as a design basis because the hydraulic conditions at maximum flow rate are un stable. For example, the sewer may suddenly run full at a X< o o *o 0 Ob O O < at RATIO OF PARTIALLY FULL TO FULL FLOW CONDITIONS Fig. 12. Ratio of partially-full to full-flow conditions. CTD014832 decreased rate of flow or under pressure at the same maxi mum flow rate. From Fig. 12, it can also be seen that the hydraulic ele ments of a sewer are: hydraulic radius (R), cross-sectional area of flowing stream (A), average velocity of flow (V), and rate of discharge (Q). The curves for R and A are the same for all diameters of pipe, but the curves for V and Q depend on the formula used in computations and on the as sumed values of R, S, and n. These effects are so small, however, that within the limits of the accuracy of pipe flow formulas, this diagram is applicable to all diameters, surface roughness conditions, and slopes of hydraulic gradients. Note that the solution of a specific problem involves four points, on four curves, all at the same relative depth, as for example Characteristic Rate of flow (Q) Depth (D) Area (A) Hydraulic radius (R) Velocity (V) Ratio to full pipe flow Condition 1 Condition 2 0.33 0.40 0.37 0.85 0.90 0.97 0.8 0.85 1.22 1114 CHANNEL FLOW CONDITIONS There are other factors and conditions that must be taken into account in the computations involved in sewer design. These conditions will be mentioned here only by brief ex planations of the meaning of the terms. For detailed discus sions, the reader is referred to standard texts on the subject of hydraulics of sewers.517 Critical depth is the depth of flow when the specific ener gy of open channel flow is at a minimum. It is expressed as where: V2 Es = d+ -- 2g Eq. 14 E, = specific energy d = depth or hydrostatic head V -- velocity Under these conditions, the depth is critical, the velocity critical, and the hydraulic gradient is known as critical slope. Critical depth is a function of the channel discharge and channel cross-section and is independent of slope or other channel characteristics. Control section is a point or cross-section where the slope of a channel changes; the critical depth occurs at that point, with the depth being greater above, and less below the point. Dropdown curve is the curve in the surface upstream from a control section, under uniform flow conditions. Backwater curve is the curve in the surface of a stream above an obstruction or sudden decrease in the slope of a channel when the velocity of flow is decreasing down stream and the slope of the invert is less than critical. Hydraulic jump is defined as a sudden transition from stream low stage at less than critical depth to high stage above critical depth. A hydraulic jump will occur when the channel bottom slope changes suddenly from greater than critical to less than critical, or when a stream at less than critical depth flows into water with a depth greater than critical. Standing wave is the term applied to a condition caused by an obstruction in a channel and resulting in a permanent rise of the surface level above normal for a short distance. Standing waves occur only when the velocity is greater than critical. Hydraulic bore, also termed traveling wave, occurs when the open channel flow rate changes suddenly at some point or changes continuously along the channel in the direction of flow. An unsteady flow exists and the hydraulic bore is created. It may travel either upstream or downstream, de pending on the immediate cause. A hydraulic bore traveling downstream is useful in sewer flushing. SEWER DESIGN Tables and diagrams4-517 have been published to aid in the design of sewers and the computation of flow condi tions, slopes, etc. Also useful is the sewer design slide rule mentioned previously. Information and diagrams are avail able on the discharge of circular sewer pipes running full at various n values in Kutter's formula. One available CTD014833 SEPTEMBER 1967 | M 15 TABLE 7--lEOOMMEiDED MINIMUM IEWU OKADEI Sawar aiza (In.) 8 10 12 15 18 21 24 27 30 36 Grad* ranoa (ft/100 ft) 0.33-0.40 0.25-0.28 0.19-0.22 0.14-0.16 0.11-0.12 0.9 -0.10 0.080 0.070 0.060 0.049 diagram4 shows the discharge capacity of clay pipe sewers for n = 0.013 for various sizes of pipes, velocities, and slopes. Diagrams of similar nature for asbestos-cement pipe (with n values of 0.010 and 0.011) are available from sev eral manufacturers. Also, diagrams similar to Fig. 12, but relating to sewers not circular in shape, have been pub lished.9 Many data tables are also available17 for use in cal culating sewer flow and design problems. All of these tools are useful to the designer. Design principles. In designing a sewer, the following principles should be kept in mind:4'9 The wetted cross-sectional area of the sewer pipe must be sufficient to handle the flow at the designed velocity. The design velocity must be sufficient to prevent strand ing of solids in the sewer, but not high enough to cause ex cessive turbulence, scour, or thrust For steep slopes, the depth of flow should be less than critical. Hydraulic jumps and dropdown curves should be avoided where pipe sizes or discharge rates change. That is, the in vert elevations should be such that the water surfaces match above and below the point of change. The depth at which the sewer is laid should be sufficient to provide for drainage of all cellars of ordinary depth. If cellars are 3- to 7-ft deep, the depth of the street sewer should be such as to provide a slope of the house connection of 1.67 ft per 100 ft. An additional 12 in. should be allowed for vertical bends in house sewers and for the depth of house sewer beneath the basement floor. In streets less than 80 ft wide, a minimum depth of 8 ft is recommended for invert of sewer laterals 24 in. or less in diameter. For larger sewers, the depth should be greater to prevent backup of sewage into basements. Where possible, to avoid unnecessary excavation, sewers should be laid parallel to the ground surface, if the ground slope is sufficient, or on a flat, but not extremely flat, grade. The slope or grade of sewers should be sufficient to pro vide a minimum flow velocity in excess of 1 fps under actual flow conditions, or 2 fps when flowing full. Maximum al lowable flow velocity should be limited to 10 fps. Velocities greater than the hydraulic critical velocity should be avoided to prevent hydraulic jump and other problems resulting from nonuniform flow. Table 7 shows commonly recom mended minimum sewer grades for pipe sizes from 8 to 36 in.; this particular table is based on Manning's formula with n = 0.10 and a flow velocity of 2 fps with the pipe running full,2 but this n-value is lower than most states allow in sewer design. Minimum pipe size should be 8 in. (some states allow 6 in.). Do not select a sewer larger than the calculated sewer size, except when the required size lies between two com mercial sizes; in this case, use the larger size. House sewers should be no less than 4 in. in diameter, preferably larger. Except under special design conditions, a sewer should never discharge into another sewer of smaller size even if the latter's capacity is larger because it has a steeper slope. Profile map. As the diameter of pipe and necessary slope are computed for each area served, a profile map of the sewer in that area should be drawn. It should show the ele M 16 I WATER AND WASTES ENGINEERING vation and grade of the sewer line as well as the depth of cut required in excavating the soil. The depth of this cut is equal to the difference between the ground level elevation and the required elevation of the bottom of the trench. The profile map should also show "top of sill" elevations of resi dences to be served, if such data are available. Shapes other than circular. The circular shape used for most sewers provides the maximum cross-sectional area for the amount of wall material required. Circular shapes are generally more convenient to manufacture, and they pro vide relatively good hydraulic qualities. The previous discussion of the hydraulics of sewage flow was based on the use of circular sewers. Shapes other than circular are used frequently, however, for one or more rea sons. For example: to provide greater strength and resis tance to superimposed loads (i.e., for structural reasons); to reduce construction costs; to make construction easier; or to improve flow conditions during periods of low flow. Among the various noncircular shapes are basket handle, catenary, egg, horseshoe, ovoid, rectangular, and semi-ellip tical. With one or two exceptions, shapes other than circular are not manufactured but are constructed in place. Flow in noncircular sewers may be calculated by substi tuting the hydraulic elements of the channel in the desired formulas. One means of calculating flow in noncircular sewers utilizes the principle of hydraulic equivalents. Sewers are hydraulically equivalent when they discharge the same quantity at the same rate, when both are flowing full on the same hydraulic gradient. Tables of hydraulic equivalent data are available,917 as are the formulas and examples of the required calculations. Sewers built in place. Concrete pipe is available in di ameters up to 144 in. Larger or smaller sewers may be con structed in place, and noncircular sewers of large size are al ways constructed in place. (Some manufactured noncircu lar shapes are available in sizes up to 108 in.) Materials for sewers built in place may be brick, concrete, or segmented tile block. Brick is almost never used in current sewer construction. Its use declined because of cost and the scarcity of skilled bricklayers. Concrete poured in place is used for large circular sewers and for nearly all noncircular shapes (except when manu factured noncircular shapes are available). The design of concrete, built-in-place sewers takes into account not only the size and flow capacity but also the shape and wall thick ness necessary for the soil conditions and depth of cover. Formulas for the design of noncircular concrete sewers exist.20 Their inclusion here is not really pertinent to this manual, which has as its principal aim the discussion of manufactured pipe. Segmented blocks of vitrified tile are made with curved inner and outer faces. These blocks may be obtained for the construction of circular sewers from 30 to 108 in. in di ameter. Use of segmented tile block has decreased. Section 5--Storm and Combined Sewers Storm sewers may be combined with sanitary systems or they may be constructed as separate systems. Usually, sep arate storm sewers are not as extensive as sanitary sewer systems. During the past 40 years or so, many storm sewers have been constructed to relieve the load on existing com bined sewer systems. In these cases, the storm sewer has often been laid parallel to a trunk combined sewer or in stalled to drain the same area served by the combined sewer. Until recently, storm water runoff has been considered to be relatively free of organic matter, although admittedly carrying suspended inorganic matter. Therefore, storm (re lief) sewers usually discharged directly, without treatment, into the nearest water course. A more enlightened view, CTD014834 Large diameter, long length clay sewer pipe In fully sheeted trench. based on studies in the past several years, is that storm water carried a relatively large amount of organic matter, as well as inert solids, and that its discharge to water courses imposes an undesirable pollution load on the receiving water. Therefore, it is now thought that storm water should be treated before discharge. Currently, considerable attention is being given to the controversy over whether or not existing combined sewer systems should be separated into two systems. If storm wa ters should be treated, as appears desirable, then separation of combined sewer systems is not the answer. Rather, it ap pears that where storm sewers are necessary to relieve flood ing conditions, adequate storm water treatment should be provided. Other approaches have been suggested. One now under study proposes that sanitary wastes be transported under pressure through small lines laid in existing combined sewers.18 In one variation of this idea currently in use, a gravity flow steel sanitary sewer is installed inside a larger storm sewer. ^ Planning V Whatever the future approach to solving the problem of storm waters, the planning and design of storm sewers is just as important as that of sanitary sewers, although the factors involved differ. A sound approach to storm water sewers is a compre hensive general plan based on future needs. Without such a plan, the construction of storm sewers often will result in a final system that is haphazard in layout, duplicating in area transversed, and inadequate in many areas. When a stepwise comprehensive plan is followed, the most effective system should be produced at the least overall expense. A storm water system, like a sanitary sewer system, re quires a preliminary survey, including information on the location of underground utilities and a map showing all per tinent data about the area to be served. There are four prin cipal steps in the design of a storm sewer system.8 These are: Determination of the best location for inlets to the sys tem; calculation of the required capacity from runoff data; computation of the required pipe size and slope; and draw ing of the profile map. Location and drainage areas Generally, storm sewers should not be located in the cen ter of paved streets, but their location is often dictated by the location of water mains, sanitary sewers, and other utili ties. The location of storm sewers also depends to a great extent on the most advantageous sites for inlets (see Part 1, Section 6) and on the topography of the area to be drained. The drainage area of a storm sewer is selected on the basis of topography rather than on the basis of an artificial * boundary as used for an area to be served by sanitary sew ers. True drainage lines are determined by the slope of paved streets, paved and unpaved property, downspout locations, and other factors. Capacity The design capacity of a storm sewer is dependent on the quantity of storm water to be handled (i.e., rainfall runoff). Any other factors, if they exist, may be disregarded. Actual ly, the rate of flow for which a storm sewer should be de signed is dependent on the magnitude of runoff rate.16 There are three general methods for determining the quantity of storm water: by empirical formulas, by flow gaging, and by the rational method of computation. Empirical formulas have been used to calculate storm, runoff for relatively small city drainage areas, particularly when the data necessary for use in the rational method are not available. Empirical formulas may be used, also, for rough preliminary computations. The most common formu las used are the Btirkli-Ziegler formula and the McMath formula. Details may be found in standard texts.8-10'17 Flow gaging to measure storm runoff has several draw backs. It requires a reasonably accurate determination of the cross-section at the point of measurement and particular attention to the characteristics of the storm being measured. The extrapolation of flow data for one Storm to other con ditions may produce misleading design bases. The rational method for computation of flow from storm runoff involves the equation where: Q = AIR Q = runoff (cfs) A = area drained (acres) I = runoff coefficient of area R = rainfall rate (in./hr) The runoff coefficient has been determined for various types of surfaces. Calculations are made for storm intensity and runoff with consideration of the maximum storm run off to be handled and allowance for the effect of storage and time of concentration of the runoff.1* SIZING STORM SEWERS The use of the rational method in determining storm quantities has been described by Gifft and Symons1* and need not be presented in detail here. In storm sewer design, the size of storm (i.e., maximum runoff) for which the storm sewer is to be designed must be decided. The design of a sewer to handle a 100-year storm (i.e., a storm inten sity that is likely to occur once in 100 years), may involve an expenditure that is too high and is Unwarranted. It is consid ered good practice to limit the storm sewer size to a 10-year storm for residential areas and to a 25- or 30-year storm for commercial districts. One factor in this decision is the liabil ity of a community for damage caused by floods. The determination of the sewer size and slope is made from consideration of the hydraulics of the system necessary for the capacity required (see Section 4). Combined sewers As indicated previously, combined sewer systems should be discouraged, but when a combined sewer system is de signed, the sizing and slope of the pipe are determined by the calculated capacity required to handle both the sanitary sewage and the storm flow. Thus, in theory, the capacity is the sum of the capacities required for sanitary sewage and storm flow, including the ground water infiltration factor. If the amount of sanitary sewage is quite small in relation to the storm flow, then the storm flow requirements will dic tate the size of the combined sewer. If industrial wastes are discharged into the sewer, they must be considered in calcu lating the capacity required. After the storm flow quantities have been calculated,1* the pipe size and slope of combined sewers are determined by the method outlined for sanitary sewers in Section 4. CTD014835 SEPTEMBER 1967 | M 17 Section 6--Appurtenances Sewer systems differ in several respects from water distri bution systems; they operate under gravity (not pressure) conditions; they contain no valves; and they include a num ber of appurtenances not used in water systems. Types of appurtenances Appurtenances are those structures or devices (not pipe) in a sewer system that are essential to proper functioning. Appurtenances may include catch basins, flow measurement devices, flush tanks, foundations, house sewers, inlets, junc tion chambers, lampholes, manholes, outlets, overflow chambers, silt basins, siphons, storm water storage tanks, traps, underdrains, ventilators, weirs, and lift stations. No attempt will be made here to delve into the details of design and construction of all of these devices. Such details may be found in a number of standard texts.5'10'20 Lift stations were covered in Manual of Practice No. 1. General comments will be made, however, on some of the other major appurtenances, particularly with respect to their rela tion to the design of sewer systems. CATCH BASINS Catch basins are used to interrupt the flow of wastewater before it enters a sewer. The velocity of flow is reduced suf ficiently to allow deposition of grit. The use of catch basins in sewer systems is decreasing because they need frequent cleaning, lead to development of odors, and provide breed ing places for mosquitoes. If sewers are designed with slopes that prevent the settling of grit, the need for catch basins is eliminated. FLUSH TANKS A flush tank is a chamber or tank in which water, or sew age, is accumulated for discharge at intervals; the discharge is used for flushing the sewer. Flush tanks are used only in sanitary or combined sewers and only where flat sewer grades cause stranding of solids. Flush tanks generally are designed to operate automatically but may be designed for manual operation. Details of flush tank design may be found in standard reference works.'10-* HOUSE SEWERS Lines that connect the street sewer to the house plumbing system are termed house sewers. House sewers are usually 4, S, or 6 in. in diameter; but the 4-in. size is becoming less and less popular. It is good practice.to standardize the house sewer size for a community. House sewers should never be connected to a street sewer of smaller size. Connections between house sewers and street sewers may be by a wye-branch or a tee-branch. Some designers prefer wyes on street sewers less than 24 in. in diameter, and tees on larger sizes, but experience in Los Angeles and elsewhere has shown that tees sacrifice little in hydraulic characteris tics while improving structural properties. The use of a 1/8 curve with a wye-branch does permit the house sewer to be laid more nearly at right angles to the street sewer. The use of water-sealed traps for ventilation control at, or just inside, the house wall is generally frowned on. Where traps are used, proper ventilation to the air is necessary to prevent build-up of pressure within the sewer, which might lead to blowing of the seal. INLETS An inlet is an opening at the street surface designed to allow surface runoff into storm or combined sewers. Inlet locations should be chosen to provide fpr the satisfactory carrying away of surface runoff. Most storm inlets are in street gutters, and the best location is one that prevents overloading of the gutters, prevents runoff across streets and sidewalks, and provides service to largest possible area. M 18 | WATER AND WASTES ENGINEERING One important factor in inlet design is the quantity of flow in the gutter. This factor may be determined by the use of Kutter's or Manning's formula. There are many other factors that must be taken into consideration,8'10'S0 but need not be discussed here. JUNCTION CHAMBERS A junction chamber is a converging section where the flow of one or more sewers is brought together for dis charge into a larger or main trunk sewer or interceptor. Principles of junction chamber design include the following; inverts of the incoming sewers should be at elevations that ensure the same normal surface flow line in all sewers; the slope of the incoming sewers should be relatively steep to ensure that when one sewer is flowing deeper than others, the backup in the sewers with smaller flow will extend only a short distance; where possible, entering sewers should be constructed on long radius curves tangent to one another to prevent turbulence in the chamber; and flow into and out of the chamber should be at the same velocity because re duced velocity of the flow from the chamber could lead to turbulence, loss of head, odors, and sedimentation. A design that will meet all of these requirements is some times difficult to obtain because of local conditions. Details of various designs of junction chambers (bell-mouth, flattop, etc.) may be found in a number of reference works.8'10'*0'21 MANHOLES A manhole is a shaft or chamber through which access from the ground surface to a sewer may be obtained for in spection or cleaning. Manholes should be placed at intervals of 300 to 500 ft, or at every point where a sewer changes in direction, size, grade, or shape. Sewers should run in straight lines between manholes. Manholes may be constructed of brick, concrete block, corrugated metal, poured concrete, or precast concrete pipe. CTD0A4836 The size and shape of a manhole are often matters of indi vidual preference. Manhole covers. Manholes should be so constructed that they can be covered by a standard cast-iron manhole frame and cover; the frame opening is usually slightly less than 2 ft in diameter. The design of the cover usually depends on the traffic load it will receive. Iron-rung steps are usually placed at convenient spacings from the top to the bottom of the manhole. Rungs should be corrosion resistant. Manhole bottoms. The bottom of a straight-line manhole is usually constructed with a half-round or split section of the sewer pipe as a channel continuation of the sewer; con crete is usually placed in the remainder of the manhole bot tom. sloping upward slightly from the top of the split section to the wall of the manhole. Junction manholes are designed and constructed as the situation demands. Drop manholes. Where lateral sewers join a main sewer located at a lower elevation, a drop manhole is installed; this allows the sewage to come in at one level and go out at a lower level. The actual design will depend on the particu lar local situation. Where the difference between the eleva tion of the two sewers is great, sewage may be allowed to fall freels from the higher to the lower sewer. This type of structure is known as a well-hole; it usually has a bottom lo cated so as to provide a cushion of water into which the sewage may fall before it flows out in the lower sewer. OVERFL OVVS XVD REGULATORS An overflow is any device or structure that permits or causes excess flow I flow above the sewer capacity) to be diverted to a relief sewer or to an outlet discharging into a receiving body of water. Most overflows are a type of weir formed b\ an opening in the side of the sewer, at a point high enough to permit the excess flow to pass to the relief channel or outlet, while at the same time causing the dryweather flow (DWF). or 2 to 5 times DWF. to continue flowing in the main sewer. This type of structure is used fre quently in combined sewer systems. Sometimes overflows involve rather elaborate designs of concrete structures. A regulator has a function similar to that of an overflow. It is a device that diverts sewage flow from one sewer to an other, particularly in combined sewer systems or storm water sewers, to prevent the surcharging of a sewer, or to regulate the amount of flow to a wastewater treatment plant. Regulators usually begin to operate when the flow in the sewer reaches a predetermined level. Regulators may be mechanical devices, leaping weirs, or side weirs; the last being essentially the same as an overflow weir. The details of design of overflow and regulator structures or devices depend on the local conditions and the purpose of the device or structure. OUTLETS The design of sewer outlets or outfall structures must be determined entirely by local condition. The outlet may be a simple concrete headwall designed to prevent undercutting of the pipe by the discharging wastewater or by movement of the receiving body of water. It may be a complex under water structure located some distance offshore at the bot tom of the river,"estuary, lake, or ocean, and designed to disperse the wastewater or treated effluent into the receiving body of water. If discharging into tidal waters or streams subject to flooding, the sewer outlet may be covered by a flap valve or automatic gate to prevent backflow into the sewer line when the water level above the outlet is higher than normal. SIPHONS A true siphon is a closed conduit, a section of which lies above the hydraulic gradeline. This condition results in a less-than-atmospheric pressure in the section above the gradeline and necessitates the use of a vacuum to start flow. An inverted siphon (also termed "depressed sewer") is a section of sewer that is lower than adjacent sections. It is so constructed to pass under a valley, a water course, or other local obstruction. An inverted siphon runs full at greaterthan-atmospheric pressure because the crown lies below the hydraulic gradeline. In general wastewater practice par lance, the term siphon is commonly used to mean an invert ed siphon, not a true siphon, although true siphons may be used in the design of flushing tank systems. Inverted siphons may be designed to meet one of three conditions: fixed elevation of inlet and outlet to provide a minimum loss of head in the siphon and to maintain a scouring velocity to prevent depositions; fixed elevation of inlet and outlet to maintain a fixed velocity; or fixed eleva tions of inlet and outlet with no limitations on head loss other than to provide a scouring velocity. Good engineering practice dictates the use of twin si phons (i.e.. two barrels), each with a pipe size of 6 in. or more. The details of design will depend on local conditions and. to some extent, on the designer's preference or judg ment. In some locations, the construction of inverted siphons may be eliminated if necessary by carrying the sewer on a light bridge across a depression. Sanitary sewers should not be carried on the floor of a highway bridge, regardless of the material of construction, because traffic vibration may weaken the joints, thereby allowing leakage. If there is no other way of solving the problem, a sewer may be carried under a bridge on hangers, or on a special truss between bridge piers. storm water tanks Storm water standby tanks are used to provide interim storage of a volume of storm water until such time as the sewer can handle it without being surcharged. The use of such structures is more common in combined sewer sys- CTD014837 SEPTEMBER 1967 ' M19 terns, where it is the intent to pass all storm water through the sewage treatment works and to avoid overflow of storm water into nearby bodies of water. These tanks are generally designed to permit overflow from the sewers into the tanks at time of surcharge and to empty back into the sewers as the flow decreases to normal. Usually, they operate under gravity conditions, but, in some cases, the stored water may be pumped back into the sewer from which it overflowed. Probably the largest storm water storage basin exists at Buffalo, N. Y.,2- where runoff from certain areas is sent into an abandoned quarry during storms to prevent street flooding. After the flow in the sewers has subsided to nor mal, the stored water is pumped back into the sewer system and passes to the wastewater treatment plant. Cleaning of the quarry following the removal of the excess water is a regular maintenance operation, as it is in constructed storm water detention tanks. Boston is installing storm water tanks and Chicago is considering the idea. TRAPS Traps are structures or devices designed to capture and hold discrete particles of various substances that are unde sirable in sewers or in treatment plants. Such devices may be used to keep grease, oil, sand, or silt out of sewer systems. These device? involve a stilling basin, where the velocity of the liquid flow is reduced sufficiently to permit separation of the unwanted material from the liquid. The principles of flotation are involved in the removal of grease and oil. Such devices are usually designed with an outlet baffle or a submerged outlet pipe and sometimes with an inlet baffle or submerged inlet as well. Silt basins operate on the principle of gravity separation of particles heavier than water (Stokes law). Such basins should be installed only in storm sewers and never in sani tary or combined sewers. They are usually designed to re duce the velocity of flow to a value between 1 and 2 fps. Velocities below 1 fps permit sedimentation of organic mat ter, and velocities above 2 fps do not permit effective sepa ration of the silt or grit. Design criteria. Design criteria for sewer appurtenances vary according to local conditions. Some basic guidelines used by the Engineering Facilities Command of the U. S. Navy are given in Table 8.23 Miscellaneous appurtenances. Other appurtenances may be designed into or as part of sewer systems, for example, lift stations. Lift stations are generally unattended and op erate automatically where the flow is relatively small. Where the flow is from large areas, these stations are usually staffed and operated accordingly. The operation of lift stations is covered in some detail in Part 2, Section 4 of Manual of Practice No. 1. Other miscellaneous appurtenances include foundations, flow measuring devices, lampholes, underdrains, and venti lators. A discussion of these appurtenances does not ap pear to be warranted in this manual. Structure Type Manhole Regular Siphons Drop Inverted Intercepting sewers Regulators Traps and Grease and interceptors oil TULE I--SUQQESTED DESIGN CRITENIA FOR SEWER APPURTENANCES** Where to use Terminally on all lines, at all junctions and changes of direction At changes in invert elevation of slope Where not otherwise required according to spacing shown in details When difference between inlet and outlet inverts exceeds 2 ft Details Pips slzs (In.) 8 Max. manhole spacing (ft) 300 10-15 18-48 48 400 500 600 For carrying sewers under ob Maintain velocity of 3 fps using struction or waterways multiple pipes as required Minimum pipe size--6 in. Pro vide overflow Where discharge of existing Where receiving combined sewers must be brought to a sewage, design for velocity new concentration point of 2.5 fps On combined systems On all outlets from subsistence buildings, garages, mechani cal shops, wash pits and other points where grease or oil can enter system Set to divert all storm flows in excess of those for which pumping and treatment facili ties are designed Displacement velocity, 0.05 fps. Grease removal--in absence of other data use 300-400 mg per L. Provide for storage of one week's grease produc tion (one day if continuous removal is provided). Length = twice depth Requirement* lower invert through manhole a distance equal to loss of head in manhole At changes in sewer size, lineup crowns Raise top of manhole above possible flooding level For difference less than 2 ft. increase sewer slope to natch crowns Use ASCE Manual No. 37. Ch. 5 for hydraulic design Take special care against infiltration resulting from depth or proximity of sur face water M 20 | WATER AND WASTES ENGINEERING CTD014838 Inplant piping at New York City Newtown Creek Pollution Control Plant. Section 7--In plant Piping Systems Inplant piping systems are used in lift and main pumping stations and treatment plants of all types. Design As in water treatment plants.24 the selection and sizing of inplant piping systems must take into consideration the use or service for which the line is intended, the pressure at which it will operate, the required flow capacity, and the fluid to be carried. Material selection is discussed in Part 2, Section 14. Layout and arrangement Inplant piping systems in wastewater treatment plants include pump suction and discharge lines for raw wastes, treated wastes, and sludges of all kinds; gas, air, and oil lines; sampling lines; chemical feed lines; sludge processing equipment lines; heating, plumbing, ventilating, and potable water systems; yard and fire protection sprinkling systems; and hydraulic and pneumatic valve operating and instru mentation systems. arrangement For any particular service, the piping should always be arranged so that any breakage or outage causes only a minimum interruption of operation. This consideration is particularly applicable to suction lines and discharge header lines in pumping systems. Piping and valves should be arranged on a systematic basis and should conform to the placement of pumps and other equipment, with a minimum of fittings and bends, so that head loss will be at a minimum. The arrangement of pipes should provide for easy access to pumps, valves, and other equipment not only for installa tion, but also for maintenance procedures. Suction piping on pumps should be carefully designed to avoid air pockets. Such lines should rise gradually to the pump, and eccentric reducers should be installed where necessary to prevent air pocket formation. Pipelines that may require repeated clean ing (e.g., raw sludge lines) should be arranged in such a way that cleaning tools can be inserted. COLOR CODING It is probably more important to color-code pipelines in a wastewater treatment plant than it is in a water treatment plant. The standard color-code of the U. S. A. Standards Institute may serve as a basis for the color coding system used in a wastewater treatment works. Whatever color cod ing system is adopted, the colors should be easily recognized in the available light at any particular location. The pipe lines should also carry lettered labels and directional ar rows at points where such information is desirable. Colors in bands may be used to indicate fluid being carried. PART 2/MATERIALS Section 1--Selection Criteria In selecting sewer pipe materials, the design engineer should base his decision on an evaluation of the compara tive physical, chemical, hydraulic, and economic character istics of the pipe or material. PHYSICAL CHARACTERISTICS There are seven principal physical characteristics to be evaluated. Size. Sewer pipe is not available in all sizes in all mate rials. If the required pipe size is larger than available manu factured sizes of a particular material, then some other material must be selected, either a manufactured product or a material to be constructed in place. Shape. Uniformity of shape for each segment (length) of pipe used is essential to ensure proper alignment, optimum hydraulic flow conditions, and ease of connection to other sections or other sewers. Sewers built in place also should have a uniform shape except where there is a change in size. Strength. The structural strength of a pipe should be suf ficient to resist failure or detrimental deformation under weights imposed on it by backfill overburden loads. The pipe must also have the strength to resist the shock of traffic loads, the ability to withstand temperature variations, and to conform to any other system design conditions. Durability. Sewer pipe is nearly always installed under ground. where it is not easily accessible. Also, sewers are designed for many years of service. For these reasons, as well as overall cost, sewer pipe should have a long life. Surface. The internal surface of a sewer pipe or its lining should be able to withstand abrasion caused by scouring action of wastewater carrying gritty materials. The external surface or its coating also should be able to withstand dam age during handling or during backfilling of trenches. Imperviousness. Sewer pipe should be impervious, to prevent leakage of water through the material. Joint characteristics. Joints should be of simple, rugged design, facilitating installation and ensuring a maximum degree of tightness, to prevent leakage in or out and to prevent the entrance of roots. Jointing materials likewise should have long life and should provide tightness. CHEMICAL CHARACTERISTICS Two chemical characteristics of pipe are important in the evaluation of sewer pipe material. Corrosion resistance. The surface of the pipe material or its coating should be resistant to true corrosion or destruc tion by electrochemical action or by interaction with any chemicals present in the wastewater. Solution resistance. Sewer pipe material should be re sistant to the dissolving action of water. HYDRAULIC CHARACTERISTICS Sewer pipe should have a smooth bore, that is, it should have a low coefficient of surface roughness, so that it will CTD014839 SEPTEMBER 1967 | M 21 provide the maximum flow capacity per inch of size with a minimum of friction loss. ECONOMIC CHARACTERISTICS The sewer pipe selected should be economical not only in original cost but also in cost of installation and mainte nance. Length of life is another factor to be considered in the overall economic characteristics. SPECIFICATIONS Once the design of the sewer is completed and the pipe materials selected, the design engineer should prepare a set of specifications for the sewer pipe. Ordinarily, the standard specifications of the American Society for Testing Mate rials are used in specifying and testing materials, but when ASTM specifications do not apply, the engineer should de velop the necessary specifications. Section 2--Design Factors Pipe used in gravity flow sewers is not subjected to inter nal pressure, except to a small degree under conditions of surcharge. Therefore, in the design of sewer pipe, internal pressure is not a significant factor. On the other hand, a sewer pipe installed in a backfilled trench carries the exter nal static and live loads placed on it. Furthermore, sewer pipe is frequently laid at greater depths than water pipe. For these reasons, the factor of external load is very important in the design of sewer pipe, regardless of the material used. In calculating loads on buried sewer pipes, the Marston load formula24'25 is generally applied. The formula is based on the theory that the load on a sewer is equal to the weight of the prism of earth (interior prism) directly above it plus or minus the frictional shearing forces transferred to that prism by adjacent prisms of earth, the magnitude of these frictional forces being a function of the relative settle ment between the interior and the adjacent prisms.2* The Marston equation (W = CwB2) is given and explained in Manual of Practice No. 2 (p. Mil).24 Marston's equation is applicable to all types of installa tions, which are usually classified as: trench, embankment, or tunnel. Trench loads Trench installations are those in which the pipe is laid in a relatively narrow trench (generally less than two pipe di ameters in width) cut in undisturbed ground, with the pipe covered by backfill to the original ground surface. External loads on sewer pipe consist of two parts: backfill (gravity earth load) and surface load; the latter results from static and live conditions that transmit their effect or impact into the ground and onto the pipe. Trench width is an important factor in the load exerted on the pipe; the wider the trench, the greater the load, until the transition point is reached. The trench width at the top of the pipe is the controlling factor, so this width should be kept at a minimum. Certainly, whenever possible, sewer pipe should be installed in a trench no wider than necessary to accomplish satisfactory bedding and jointing. GRAVITY EARTH LOADS External loads resulting from backfill are calculated by the Marston load formula as indicated previously. Accord ing to Spangler,25 the portion of total load within a ditch that will be carried by the pipe depends on the relative ri gidity of the pipe and the fill material that does not lie di rectly above the pipe (i.e., sidefill). Rigid pipe, in a situation where the sidefill is relatively compressible, must carry practically all of the load. In the case of relatively flexible, thin-walled pipe, with the fill thor oughly tamped at the sides of the pipe, the sidefill will carry some of the load. Table 9 shows trench loads calculated according to the Marston formula, assuming that the soil is granular without cohesion and that it weighs 100 lb per cu ft. For soils of other densities, these data should be multiplied by a proper factor; the factor depends on the weight and the cohesive ness of the soil.26 There are many cases where the trench load formula is less accurate than the positive projecting embankment for mula (see below), because the transition point from trench to embankment is a function of the height of backfill to width of the ditch at the top of the pipe and the pipe di ameter. The use of the trench load formula would lead to overdesign of the pipe for those cases where the actual width of trench is greater than the transition width. It might be more economical with respect to pipe class to use the embankment formula where it is applicable. SUPERIMPOSED LOADS Static superimposed loads are caused by structures sup ported on the soil above the pipe, such as streets, buildings, TABLE I--TRENCH LOADS (LB PER LIN FT) FOR DIFFERENT TRENCH WIDTHS AND DEPTHS4 Depth of )f pipe (t> 4 5 6 7 8 9 10 12 14 16 18 20 22 24 26 28 30 -- 2 550 640 700 740 800 860 880 940 960 1000 1000 1020 1030 1040 1040 1040 1040 2-% 725 855 935 1030 1130 1160 1250 1370 1440 1470 1500 1560 1560 1590 1590 1610 1620 Trench width at top of plpo (ft) 3 S-V4 4 900 1060 1200 1350 1440 1570 1600 1800 1930 2020 2070 2120 2160 2250 2250 2250 2300 1015 1350 1530 1650 1840 1960 2080 2230 2450 2650 2750 2820 2880 2940 3000 3080 3060 1280 1440 1760 2000 2460 2300 2480 2800 2960 3200 3440 3510 3600 3600 3680 3840 3910 5 1875 2000 2250 2500 2950 3120 3380 3750 4120 4500 4750 5000 5250 5500 5620 5620 5750 * Data are for granular soil without cohesion, weighing 100 lb per cu ft, based on broad fills. 6 2160 2600 2880 3240 3600 3960 4320 4850 5400 5950 6300 6500 7200 7200 7550 7900 7900 M 22 I WATER AND WASTES ENGINEERING CTD014840 etc. Live loads are caused by traffic. These superimposed loads may be calculated by the formula (also developed by Marston) that appears as Eq. 5 in Manual of Practice No. 2 (p. Mil).21 This equation contains an impact factor for moving traf fic. In the case of sewers, which are usually laid more than 6 ft deep, the calculation of live loads is generally not uti lized in calculating the pipe design. Superimposed static loads and, where depth of cover is less than 6 ft, live loads should be calculated and included in the pipe design. Embankment loads A sewer may be constructed so that its top is at or near the natural ground surface, and then covered with an embankment.-'0 When the top of the sewer is somewhat above the natural ground surface, it is termed a positive projecting conduit. A negative projecting conduit is one in stalled in a relatively shallow trench, with its top below the natural ground surface. The trench above the pipe is then backfilled and compacted and the embankment constructed to the finished grade by ordinary methods. This type of construction gives a greater depth of fill than a positive projecting conduit. This increased depth plus the compress ibility of the loose fill ensures that the prism over the pipe will settle more than that of the adjacent prisms, thus creat ing upward shearing forces that relieve some of the load on the pipe. An imperfect ditch conduit is constructed as follows: first, the pipe is installed as a positive projecting conduit; then an embankment is built to some height above the pipe and compacted as it is placed; next, a pipe-width trench is excavated directly above the pipe in the embankment down almost to the top of the pipe; and finally, the trench is filled with loose compressible material, and the balance of the embankment is completed in the normal manner. Formulas for positive projecting, negative projecting, and imperfect ditch embankment installations and a discussion of tunnel installations are given in various design manuals.20 As indicated previously, there may be cases where em bankment type construction will result in economy, particu larly with respect to the required class of pipe. Supporting strength The load carrying capacity or supporting strength of a sewer pipe depends on the pipe shape, pipe material, and type of bedding used. Three terms are used in connection with supporting strength, and they have different meanings and values. They are: "supporting strength" (the three-edge bearing test); "safe supporting strength," which depends on the type of bedding used in the trench; and "field support ing strength." which is the safe supporting strength multi plied by a safety factor. THREE-EDGE BEARING TEST As in the case of water pipes, the simplest, most easily performed, and most accurate test for determining support ing strength (crushing strength) of a pipe is the three-edge bearing test (see Manual of Practice No. 2, Fig. 5, p. M10).24 There are three other methods for determining supporting strength, and if used, data from these tests may be converted to three-edge bearing test equivalents by di viding the observed results by appropriate factors. In all of these tests, the results are reported in terms of pounds per linear foot. The results of the three-edge bearing test provide a basis for determining the resistance to crushing loads under standardized laboratory test procedures. When the pipe is installed, its supporting strength (resistance to crushing) is increased by virtue of the bedding on which it rests. Four types of bedding are shown in Fig. 13.23 - I S BEDDING -LOAD IOAD FACTOR FACTOR = 1.9 : 2.2S - 3.4 Fig. 13. Types of bedding for sewer pipe." Bedding conditions. These four bedding conditions have been designated as A, B, C, and D by the ASCE and WPCF Manual on Sewer Design.20 That manual also contains a computation diagram for determining earth loads on buried pipes under the several conditions of bedding. The support ing strengths of sewer pipes under these bedding conditions are all greater than the three-edge bearing strength. The rel ative factors for comparing each to the three-edge bearing test are shown in Fig. 13 and below. Bedding types are de scribed as follows. Impermissible or flat bottom--Class D (load factor, l.l). Little or no care is exercised to shape the foundation to fit the pipe. Secondy, little care is taken in backfilling to make sure that the materia! used is of good granular quality or is at least partially compacted under and around the pipe. Spangler23 strongly discourages the use of this type of bed ding. Ordinary--Class C (load factor 1.5). Ordinary care is exercised to shape the foundation to fit the pipe reasonably well for a width of at least one half the pipe diameter. Back fill must be lightly tamped to a depth of 6 in. over the top of the pipe. First class--Class B (load factor 1.9). Bedding consists of fine granular material (crushed stone or pea gravel) on an earth foundation carefully shaped to fit the pipe for at least 60 percent of its diameter, or compacted granular material with tamped backfill. The backfill must be tamped in two layers of 6 in. each over the top of the pipe. Concrete cradle--Class A (load factor 2.25 to 3.4). Bed ding consists of plain or reinforced concrete of suitable thickness placed under the pipe and extending upwards around it to some depth less than the pipe radius. Another Class A bedding consists of a concrete arch construction with a load factor of 2.8 to 4.8. (This type of construction is described in Part 2. Section 7.) Concrete encasement (load factor greater than 1.0). In this type of bedding, sewer pipe is encased in concrete to a thickness of 2 in. or more. The supporting strength de pends on the compressive strength and thickness of the concrete and on the size of the pipe; the load factor also depends on these factors. SAFE SUPPORTING STRENGTH As indicated, the actual load that a pipe will support de pends on the type of bedding. The "safe supporting strength" is calculated from the load factors noted above. These safe supporting strengths are shown in Table 10. Al though data are included on the impermissible bedding con dition, the use of this type of flat bottom bedding is not recommended. SAFETY FACTORS It is good practice to include a safety factor in the engi neer's specification of class of sewer pipe to be used on a particular installation. For rigid manufactured sewer pipe, a CTD014841 SEPTEMBER 1967 I M 23 TMLE II--SUPPORTING! STRENGTHS (LI PEI LIN FT) OF SEWER PIPE FOR DIFFERENT BEDDING CONDITIONS First Thrao 1lmp*rmitiblt Ordinary clots odgo badding badding bodding bearing (load factor (load (load factor strengths in factor 1.5) 1.9) Concrete cradle bodding (load factor Z:ZS-3.4) 1100 1300 1400 1500 1750 2000 2200 2400 2750 3200 3500 3900 4000 50U0 1210 1430 1540 1650 1925 2200 2420 2640 3025 3520 3850 4290 4400 5500 1650 1950 2100 2250 2625 3000 3300 3600 4125 4800 5250 5850 6000 7500 2090 2470 2660 2850 3325 3800 4180 4560 5225 6080 6650 7410 7600 9500 2475-3740 2925-4420 3150-4760 3375-5100 3938-5950 4500-6800 4950-7480 5400-8160 6190-9350 7200-10880 7875-11900 8775-13260 8800-13600 11,000-17,000 safety factor of 1.2 to 1.5 is recommended. That is, once the safe supporting strength is determined, it is multiplied by a factor of 1.2 to 1.5 to obtain the "field supporting strength," which serves as the basis for specifying the pipe class to be installed. For reinforced concrete sewer and culvert pipes, it is customary to design on the basis of 80 percent of the ulti mate load, or 100 percent of the load necessary to produce a 0.01-in. crack, whichever is less. applicability of data These data and comments on sewer pipe design are gen erally applicable to most types of manufactured pipe. Where differences from these design practices apply for specific pipe materials, the matter will be covered in the dis cussion of the particular material. Sewers constructed in place also have different design considerations, depending on size, shape, and material. Section 3--Asbestos-Cement Pipe The same materials, processes, and testing procedures are used in the manufacture of asbestos-cement nonpressure sewer pipe and building sewer pipe as in the manufacture of pressure pipe for water supply systems. The subject of man ufacture is covered in Manual of Practice No. 2 (pages M10 to M13).24 Pipe characteristics There are three types of asbestos-cement pipe: building sewer pipe, gravity sewer pipe, and pressure sewer pipe. In the selection of pipe, the design engineer must consider, in addition to application, characteristics of the pipe material. PHYSICAL CHARACTERISTICS Asbestos-cement building sewer pipe is supplied in Class 1500. Nonpressure sewer pipe is generally available in Classes 1500, 2400, and 3300, and sometimes in Classes 4000 and 5000. These class designations are based on sup porting strengths as determined by the three-edge bearing test. Pressure sewer pipe is available in Class 100, Class 150, and Class 200, based on the combined internal and external loading theory.24 Table 11 shows data on the available pipe diameters and lengths and the weight per foot in the different classes. These weights per foot are approximate and include the weight of one coupling attached to the pipe length. The weights given in Table 11 are approximate and may vary slightly from one manufacturer to another. M 24 I WATER AND WASTES ENGINEERING Well-point dewatering system along fully-sheeted trench for 24-in. asbestos-cement sewer pipe. SURFACE CHARACTERISTICS The need for a smooth bore in sewer pipe has been point ed out previously. Manufacturers of asbestos-cement sewer pipe meet this criterion through the method of manu facture, which utilizes a polished steel mandrel around which the pipe is formed. The resulting product has a Kutter or Manning n value of 0.010. After curing, the material has a low content of uncombined calcium hy droxide. The flow characteristics are relatively unaffected by continued use. Linings Asbestos-cement sewer pipe is normally unlined. An epoxy-lined pipe is available for use in special applications. This epoxy material is applied free of solvents, and the lin ing, therefore, has no holidays attributable to solvent evapo ration. Pipe joints and fittings are also available with epoxy linings. The surface of epoxy-lined pipe has a roughness coefficient equal to or better than that of unlined pipe. Joints and fittings Nonpressure asbestos-cement sewer pipe and house and building sewer pipe use the same type of couplings, with flexible rubber rings, as does water pipe. These couplings provide a joint that is both leakproof and rootproof. Fittings of all types and for all uses are available for join ing asbestos-cement pipe to other sewers constructed of any material. Specifications In the preparation of specifications for asbestos-cement nonpressure sewer pipe, the design engineer should specify that the manufacture and material meet the requirements of the latest revision of the Federal Specification SS-P-331 and ASTM Specification C-428. Asbestos-cement pressure sewer pipe is specified bv Federal Specification SSP351a, AWWA C-400-65, and ASTM Des. C-296-65T. Manufacturers Asbestos-cement sewer pipe is manufactured by the fol lowing companies: Cement-Asbestos Product Co., Woodward, Ala. Certain-teed Products Co., Ambler, Pa. Flintkote Co. (Orangeburg Mfg. Div.), Orangeburg, N. Y. Johns-Manville Corp., New York, N. Y. CTD014842 Available lengths (in.) (t> 4 5. 6-1/2, 10. 13 5 5, 6-1/2, 10,13 6 5, 6-1/2,10,13 6 5, 6-1/2,10,13 8 5, 6-1/2, 10, 13 10 6-1/2,13 12 6-1/2,13 14 6-1/2, 13 15 6-1/2, 13 16 6-1/2, 13 18 6-1/2, 13 20 6-1/2,13 21 6-1/2, 13 24 13 27 13 30 13 33 13 36 13 39 13 42 13 TAILE 11--CHABACTEWSTICS OF ASBESTOS-CEMENT PIPE Approximate weight par fool (lb)* (with coupling attechod) Claes 1500 Class 2400 Class 3300 Class 4000 Class 5000 4.6-5.0 6.4-6.7 7.7-8.7 BUILDING AND HOUSE SEWERS 5.0-5.6 6.9-7.7 8.8-9.2 5.7 8.9-9.4 10.3-11.1 8.1 12.8-13.1 16.1-17.1 22.2-29.9 25.9-27.7 28.4 31.5-33.3 GRAVITY SEWERS 8.8 12.8-14.0 16.1-17.7 23.0-24.0 25.9-28.9 28.4 31.5-35.3 40.3-42.0 46.3-48.9 50.1 56.1-64.3 10.4 14.5-15.8 17.8-20.5 24.9-27.0 29.7-34.0 33.1 34.5-41.1 45.6-48.9 52.2-57.1 58.7 70.8-74.5 89.3 104.8 20.0-22.7 21.9-25.8 26.6-29.6 29.6-33.6 31.1-37.3 34.1-42.0 35.2 39.3 37.1-45.4 40.9-51.0 50.7-54.2 53.4-60.6 59.0-63.0 61.7-70.6 66.3 72.5 78.9-82.3 81.4-92.2 96.6 110.4 115.9 128.9 133.5 148.7 152.2 . 169.8 ' 198.0 216.0 Class 000 Class 7000 a9.0 290.0 238 260 Weight per loot will vary with pipe length because total weight includes attached coupling. Weight per foot also varies from one manufacturer to another; above ranges are from two manufacturers. Section 4--Bituminized Fiber Pipe Laminated-wall, bituminized-fiber drain and sewer pipe is designed to have a resistance to external loads, chemicals, heat, and water. It is manufactured in accordance with Fed eral Specifications SS-P345a and Commercial Standard CS 226-59. Homogeneous bituminized-fiber pipe is also manu factured in accordance with Commercial Standards CS11654, but this type of pipe is not covered in this section. Manufacture The process of manufacturing laminated-wall bitumi nized fiber pipe consists of two major steps. The first step is the forming of the pipe as a multiple laminated or spiral fi brous structure of tough uniform fibers bonded with a spe cial water resistant adhesive. The second step is impregna tion of the formed pipe, under high pressure, with an especially compounded liquefied pitch. TTie result is a pipe with a dense wall and smooth interior surface, free from obstructions or rough flaky areas. Testing To ensure that the pipe as produced by the manufactur ing process meets specifications, samples are tested to de termine their strength with respect to crushing, axial-com pression crushing, surge pressure, and hydrostatic pressure, and to determine their resistance to flattening pressures, chemicals, kerosene, hot water, and heat. Tests are also made to determine resistance to the absorption of water and to longitudinal permeability seepage. All tests are conducted with standardized equipment and controlled procedures. MINIMUM TEST CRITERIA Table 12 lists the minimum acceptable test criteria for physical strength characteristics. In addition to the criteria in Table 12, laminated-wall, bituminized fiber pipe must have the following characteris tics. Chemical and kerosene resistance. Both pipe and fittings must be highly resistant to corrosive soils, acids, alkalies, salts, and petroleum wastes. After being subjected to the chemicals under test conditions, the crushing strength of the samples must not be less than the values indicated in Table 12. Tests are made by subjecting separate samples, for pe riods of 10 days at 70 to 80 F, to 0.1 N sulfuric acid, 0.1 N sodium carbonate, 0.1 N sodium sulfate, and kerosene. Then the test specimens are emptied, rinsed, wiped dry, and tested for crushing strength. Flattening resistance. Both pipe and fittings must resist the combined flattening effects of earth loads and heat. Pipe size* (in.) 2 3 4 5 6 8 10 12 15 18 TABLE 11--MINIMUM REQUIRED PHYSICAL CHARACTERISTICS FOR BITUMINIZED-FIBER PIPE Federal SpedSealieu SS-P-MSa Wall thickness (in.) 0.25 0.28 0.32 0.41 0.46 0.57 0.61 0.61 0.67 0.71 Axial crushing (Ib/lin ft) 6.000 10,000 13,000 20,000 30.000 39,000 60,000 72,000 98,000 125,000 Physical strength tests Beam (Ib/lin ft) 1,000 1,000 2,200 4,200 4,400 7,000 7,500 8,500 10,000 11,500 Crushing (Ib/lin ft) 1,500 1.500 1,500 1.500 1,500 1,800 1,800 1,800 1,800 1,800 Hyd restatic pressure (P*i> 350 350 350 350 300 300 200 150 150 100 Nominal inside pipe diameter. Surge pressure (psi) 600 600 600 600 500 500 350 350 250 250 CTD014843 SEPTEMBER 1967 | M 25 House sewer connection being set into 12-in. bituminized fiber sewer pipe. Tests are made by subjecting two 3-in. lengths to a dead weight load at a temperature of 150 2 F for 48 hr. The dead-weight loads differ for different pipe diameters, (110 lb per lin ft for pipe 2- to 4-in. diam., 130 lb per lin ft for 5and 6-in. pipe, and 160 lb per lin ft for pipes of 8- to 18-in. diam.). After cooling to 75 F, the decrease in inside diame ter may not be more than 2 percent. Heat resistance. Specimens selected at random must show a resistance to heat, that is, after being subjected to a tem perature of 180 F for 8 hr, while laid on a flat surface, the test specimens must show no appreciable exudation of bituminous material nor any flattening or other distortion. Hot water resistance. Pipe specimens must be able to withstand the effects of boiling water. There must be no evidence of disintegration or separation into laminations during a 6-hr test. Inspection for such damage is performed after the specimens have been cooled in water at 70 F for 2 hr (or dried overnight at 70 F). Longitudinal permeability. To test for longitudinal per meability, pipe samples with machined ends joined by a coupling are subjected to water pressure of 5 psi for 1 hr and are examined for movement of water into die pipe lon gitudinally through the pipe ends. Following the test, no ap preciable amount of water should emerge from the ends of the pipe. Water absorption. Weighed pipe samples, immersed in water at 75 F for 48 hr, then wiped clean and dry, should not increase in weight by more than 2 percent of the dry weight. Surface characteristics Laminated-wall, bituminized fiber pipe as produced for commercial use has a smooth bore. According to the manu facturers, calculations of flow capacity may be based on a Kutter or Manning n value of 0.010, but design engineers usually use an n value of 0.012 to 0.015. Joints Unless otherwise specified by the design engineer on a project, the ends of bituminized-fiber pipe are tapered to fit within couplings that are also tapered inside. Pipe lengths of more than 10 ft are usually furnished with plain M 26 i WATER AND WASTES ENGINEERING TMIE It--CHARACTERISTICS OF SOME COMMERCIALLY AVAILABLE IITUMINIZED-fltER FIFE* Pip* lize (in.) Wall thlcknasa (In.) Lan^th Weight (Ib/lin ft) Crushing strength (Ib/lin ft) 2 0.260 10 1.1 3 0.29 10 1.9 4 0.34 10 2.7 2100 6 0.29 20 3.7 6 0.34 20 4.5 6 0.39 20 5.0 6 0.48 10 6.8 2900 8 0.34 20 6.0 8 0.39 20 6.8 8 0.44 20 7.7 8 0.57 10 10.8 2650 8 0.57 15 10.8 10 0.45 20 8.7 2000 12 .0.54 20 12.9 1800 12 0.57 15 15.0 15 0.56 20 16.8 1800 18 0.70 20 24.0 1900 The data in this tabla do not necessarily apply to all commercially available pipe. ends. Joints with couplings are watertight. Couplings used for jointing are subjected to rigid testing for strength, etc. In addition to the standard coupling of bituminized fiber, couplings are also made of butyl rubber and neoprene. Commercially available pipe Table 13 lists the characteristics of typical commercially available pipe. Some commercial products have dimensions and properties that are well above the minimum values specified in Federal Specifications SS-P-345a. Laminated-wall, bituminized-fiber pipe is also available in sizes between 18 and 48 in. in diameter. All sizes may be obtained as perforated pipe for use in septic tank drain fields (in small sizes) or for land drainage (in large sizes). SHIPPING Laminated-wall, bituminized-fiber pipe is crated and shipped by rail (minimum load weight, 36,000 lb), or by truck (minimum load weight, 30,000 lb). Manufacturers Laminated-wall, bituminized-fiber pipe may be obtained from the following manufacturers: Kyova Pipe Co., Ironton, Ohio Orangeburg Mfg. Co., Div. of Flintkote Co., Orangeburg, N. Y. Robinson Clay Pipe Co., Akron, Ohio Sonoco Products Co., Hartsville, S. C. Section 5--Brick and Clay Blocks Bricks and vitrified segmented tile blocks are manu factured by firing a clay mixture in a kiln under controlled conditions. The composition and method of manufacture affect the characteristics of the product. Bricks and tile blocks currently are seldom used in sewer construction because of the high cost of skilled labor re quired for installation. In some instances, however, liner plates of vitrified clay are used to protect the invert of a concrete sewer against erosion. Brick is sometimes used in the construction of manholes, but in recent years, concrete has largely replaced brick for this application. Where brick or segmented tile blocks are used, they are usually obtained from the nearest possible point of manu facture. CTD014844 Because this manual is devoted principally to the subject of sewers constructed of manufactured pipe, the processes for manufacturing brick and tile blocks will not be covered. Manufacturers As brick sewers are built in place and do not utilize a 0k manufactured pipe product, no listing of manufacturers is v considered to be necessary. Manufacturers of vitrified clay tile blocks and liner plates are generally the same companies that manufacture clay sewer pipe (see Section 7). Section 6--Cast Iron Pipe Cast iron pipe, manufactured in the same way as for wa ter supply systems, is generally specified for installation where the sewer is to be exposed, where there is expected to be internal pressure (as in force mains) or unusual external load or settlement; or where tight joints are needed to limit infiltration (as in a stream crossing). According to the Cast Iron Pipe Research Association,27 s the same general type of cast iron pipe is used for convey ing sewage as for conveying water. Therefore, the same design procedure is applicable to both water and sewer pipe, > except that in the case of gravity sewers, where there is no internal pressure, it is not necessary to use a factor of safety as high as that recommended for buried pressure pipelines. Cast iron pipe is also used in wastewater treat ment plants. In all cases, the class designation is given in terms of the pressure to be encountered. There is a nonpressure cast iron pipe, sometimes termed soil pipe, that is manufactured in small sizes for use in house sewer systems or building drains. The process of manufacture is essentially the same as for cast iron pressure pipe. Because the design and manufacture of cast iron pipe is Cthe same whether the pipe is used in a water distribution system or in a sewer, the discussion of these subjects will not be reviewed here. The subjects appear in sufficient de tail in Manual of Practice No. 2 (pages M14 to M17).24 Manufacturers Manufacturing companies that produce cast iron pipe in clude the following: Alabama Pipe Co., Div. Woodward Iron Co., Anniston, Ala. American Cast Iron Pipe Co., Birmingham, Ala. Buffalo Pipe & Foundry Corp., Buffalo, N. Y. James B. Clow & Sons, Inc., Chicago, 111. Griffin Pipe Products Co., Oakbrook, 111. Lynchburg Foundry Co., Lynchburg, Va. McWane Cast Iron Pipe Co., Birmingham, Ala. Shahmoon Industries, Inc., Warren Foundry & Pipe Divr, New York, N. Y. ' Traverse City Iron Works, Traverse City, Mich. United States Pipe & Foundry Co., Birmingham, Ala. R. D. Wood Div., Griffin Pipe Products Co., Florence, N. J. Twin force mains (36-in. ductile iron pipe) for river crossing at Kansas City, Kan. Section 7--Clay Pipe Clay pipe was probably first used to carry water and wastes in Babylon, more than 5000 years ago. Clay pipe drains were found in the ruins of an ancient palace built about 1400 B.C. on the Island of Crete. With the beginning of modern sanitary practices, in about the mid-1800's. clay pipe sewers became widely used in Europe and America. The first clay sewer pipe in Boston was reportedly 28 laid prior to 1700; it was handmade. Probably the first factorymade clay pipe was hexagonal water pipe manufactured at Middlesbury. Ohio, in 1849. In the succeeding 50 years, al though clay pipe was manufactured extensively in the Unit ed States, the clay pipe industry was concentrated in Ohio, Tennessee, and the Carolinas.28 The use of clay sewer pipe grew as population increased and sewer systems were ex panded. TAMPED SOIL B A ^4 IN. CRUSHED STONE BEDOING TO SPRING LINE Fig. 14. Special method of laying clay pipe to increase sup porting strength. Design In the early years of clay pipe manufacture, no consider ation was given to the various design factors necessary to produce pipe that would withstand loads imposed on it. Now, however, as a result of continued research, the manu facturing processes are controlled to produce a product that will meet conditions of service. According to ASTM Des. C13-65T, clay sewer pipe may be either glazed or unglazed. FACTORS OF DESIGN Selection criteria, as previously presented in Part 2, Sec tion 2, apply to clay pipe. So, too, do the design factors (trench loading, supporting strength, and safety factors) as presented in the same section. These design factors are reflected in standards issued by ASTM, the United States of America Standards Institute (USASI), and the federal government. The National Clay Pipe Institute has prepared a list of these specifications (Table 14). TABLE 14--CLAY PIPE STANDARDS AND SPECIFICATIONS* Designation* ASTM USASI C-4 Title of specification Specifications for clay drain tile C-12 A 106.2 Recommended practice for installing vitrified clay pipe C-13 A 106.3 Specifications for standard strength vitrified clay pipe C-32 A 100.1 Sewer brick--clay or shale C-200 Specifications for extra strength vitrified clay pipe C-301 A 106.5 Testing of vitrified clay pipe C-425 Specifications for jointing vitrified clay pipe ASTM as American Society for Testing Materials, 1916 Race St., Phila delphia, Pa. USASI *= United States of America Standards Institute, 70 E. 45th St., NewYork.N.Y. 10017. CTD014845 SEPTEMBER 1967 | Nl 27 Pip# sis# (in.) 4 6 8 10 12 15 18 21 24 27 30 33 36 TABLE ti DESIGN CHARACTERISTICS OF CUT PIPE Crushing strength (Ib/lln ft)** W#ight (Ib/ft) Standard strength Extra strength Standard strength Extra strength 1200 1200 1400 1600 1800 2000 2200 2400 2600 2800 3300 3600 4000 2000 2000 2200 2400 2600 2900 3300 3850 4400 4700 5000 5500 6000 8. 14. 21.5 31.5 43.5 67.5 96. 137. 171.5 225.5 270. 330. 390. 10. 15.5 24. 36.5 55. 90. 116. 180. 218. 256. 334. 424. 504. ASTM Specification: standard strength--C13; extra strength--C2Q0. Three-edge bearing test, f Flowing full or half full. Hydraulic rad lust <K) 0.083 0.125 0.167 0.208 0.250 0.312 0.375 0.437 0.500 0.556 0.625 0.687 0.750 External loads. Two types of clay pipes are available: standard strength and extra strength. Tbe minimum crush ing strength for each, as allowed under ASTM Specifica tions C-13 and C-200, is shown in Table 15. As indicated previously, this minimum allowable crush ing strength (three-edge bearing test) becomes the basis for the calculation of supporting strengths for the type of bedding used. For design purposes, supporting strength value should be multiplied by a safety factor of 1.2 to 1.5. As an alternate to using extra-strength pipe to obtain greater supporting strengths, it is possible to use a special bedding method, termed arch encasement.4 The method (see Fig. 14) consists of placing the pipe on a bed of 1/4 to 3/4-in. crushed stone, adding stone around the pipe up to the springline, and pouring a concrete arch cap over the pipe. Backfill should be carefully tamped, both at the sides and on top of the arch. With this type of bedding, the sup porting strength of the encased pipe is 3.5 times the mini mum three-edge bearing crushing strength. Even with poor underbedding, a load factor of 2.25 times the three-edge bearing test strengths may be obtained by arch encasement. The use of reinforcing bars in the concrete reduces the amount of concrete required. Pipe characteristics With respect to clay pipe, the characteristics that must be considered in selection include not only crushing strengths Large diameter clay sewers laid in concrete cradle construc tion. (Table 15) and physical measurements, but also several other characteristics, some of which are not covered by spe cifications. Allowable absorption. In the specified test for absorption, pipe is immersed in boiling water for 5 hr, then cooled and wiped dry. The maximum gain in weight caused by water absorption is limited to 8 percent.' Acid resistance. Where acid resistance of the pipe is a consideration, the acid-soluble material in the pipe is limited to 0.25 percent by weight. Nonspeclfied characteristics. In addition to the character istics covered by ASTM specifications, there are several other characteristics that should be considered by the design engineer. Abrasion resistance is important in sewers carrying com bined wastes and storm water. Many cities in this country have clay pipe sewer systems that have been in service more than 100 years. This long experience record attests to the abrasion resistance characteristics of this type of pipe. Deformation resistance is related to pipe strength Under design conditions, and in the three-edge bearing test, the change in pipe shape under load is negligible up to the point of pipe failure caused by loads in excess of the supporting strength of the pipe. Long life is a characteristic attested to by the history of sewers both in ancient and modem installations. PHYSICAL CHARACTERISTICS. Physical measurement characteristics have been pub lished in detail.4 Pipe is commonly available in sizes from 4 to 42 in. in internal diameter (see Table 15); the nominal minimum length is 2 ft for pipe up to 12 in. in diameter, and 3 ft for pipe of larger size. Pipe is also generally avail able in 4, 5, and 6 ft lengths. Barrel thickness may vary within allowable limits. For example, for 4-in. pipe, the nominal wall thickness is 1/2 in., but the minimum allowable thickness is 7/16 in.; for 36-in. pipe, the nominal wall thickness is specified at 2-3/4 in., but the allowable minimum is 2-5/8 in. The outside di ameter of the pipe barrel may vary from 4-7/8 in. to 5-1/8 in. for 4-in. pipe, to 40-3/4 in. to 40-1/4 in. for 36-in. pipe. Limits are also placed on socket size and depth. Straightness of pipe lengths is specified: maximum allow able deviation is 1/16 in. per ft of length. Weights of clay pipe per foot of length increase with in creases in pipe size; see Table 15. Hydraulic characteristics of vitrified clay pipe are indicat ed by an n value of 0.013 (Kutter or Manning) generally used by design engineers for pipe of all sizes. Where clay sewer pipelines are laid with careful attention to grade, straightness, and best possible jointing, and where flow ve locities provide self scouring at all times, n values as low as 0.011 have been used in calculations of flow capacity. Table CTD014846 15 shows the hydraulic properties of clay sewer pipe of dif ferent sizes. Manufacture The manufacture of clay pipe begins with the selection and mining of clays having desirable composition and characteristics.-'5 MATERIALS Three types of clay are considered acceptable by ASTM: surface clay, occurring at the earth's surface in an unconsol idated and unstratified condition; fire clay, a sedimentary clay of low flux content; and shale, a thinly stratified, con solidated, sedimentary clay, with well-marked cleavage par allel to the bedding. Clay pipe may be made from any one of these substances or from a combination of two or three of them. Approximately 2400 lb of clay is required to make 1 ton of clay pipe. PROCESS After mining and storage at the plant, the clays are ground to pass a screen of 10 to 16 mesh per in. The var ious clays are then blended to produce the desired quality pipe. Tempering and mixing. The ground clays, when blended, are moistened and mixed (tempered) in a pugmill or simi lar mixer to" produce a smooth, homogeneous mass having the consistency of modeling clay. Pressing. "Green" pipe is formed by extruding the tem pered clay through a die under pressures of 750 to 2000 psi. Any entrained air left after mixing is expelled in the press ing process. Removal of air ensures that blisters and lamina tions will be avoided in the steps that follow. The forming of the pipe is accomplished by steam-operated vertical presses or by horizontal extrusion presses. Today, all opera tions are automatic or semiautomatic. Both the pipe barrel and bell are produced in the pressing or extrusion operation. The green pipe is an extremely dense mass composed of about.82 percent clay and 18 percent water, by weight. Formed green pipe is quite heavy in the larger sizes; for example, a 5-ft length of 36-in. pipe weighs 3500 lb in the green condition. The pipe is also larger than final desired size to allow for shrinking in later operations. Green pipe is strong enough to stand on end without slump ing during its transfer from the pressing operation to curing. Following pressing, the pipe is cut to the desired length. Vitrified clay pipe for use in sewers is made with bell and spigot ends, except on order for special conditions. Fittings, such as wyes. tees, saddles, elbows, slants, etc., are. also made by an extrusion process. In addition to the usual bell and spigot type of joint, there is also an "O" ring joint avail able. Curing. To reduce the moisture content of the green pipe to 3 percent or less, the pipe is dried (cured) in a warm, moisture-controlled curing room. This operation is neces sary to prevent the formation of steam within the pipe dur ing the firing process. During curing, the pipe remains on end, with the bell up. Curing time depends on the pipe size; 4-in. pipe may dry in 1 to 3 days, while a 36-in pipe may require 1 to 3 weeks. In the drying process, the pipe shrinks to its final size. After it has been dried, the pipe is hard and firm and ready for the next step in the manufacturing process. Firing. The final strength of clay pipe depends on a fu sion of clay particles under extreme heat. This process, termed firing, takes place in either a beehive furnace or kiln (batch operation) or in a tunnel furnace (continuous operation). For the first few hours of the operation, the furnace tem perature is held at about 200 F to drive off residual moist ure in the cured pipe. This part of the process is termed "water smoking." When the pipe is thoroughly dried, the furnace temper ature is increased to 900 to 1400 F, at which point organ ic matter and certain minerals in the clay are burned. This part of the process is termed "oxidation;" the gases formed in the burning are driven off before the pipe becomes too dense to permit their escape. Following oxidation, the furnace temperature is raised quickly to 1900 to 2200 F, at which point the clay vitrifies. The final temperature used depends on the constituents of the clay. During the vitrification process, particles with a high heat resistance form the skeleton structure of the pipe. Around this skeleton, materials of lower melting point flow to form a dense hard, coherent mass. Cooling. After firing, the temperature of the furnace and the pipe is reduced slowly at controlled rates to prevent cracking of the pipe. The composition of the clays used is a factor in the cooling rate used. TESTING When the pipe is cool enough to handle, it is subjected to a series of tests. The first of these is the "hammer test," in which each length of pipe is tapped lightly with a hammer. If a pipe does not have a bell-like ring when tapped, it is re jected. Other tests are made on random samples of each batch, in accordance with standard procedures set forth in ASTM specifications. (See Table 14 for name and number of spe cifications.) These tests include: crushing test (three-edge bearing test); acid resistance (48-hr immersion in nitric, sulfuric, hydrochloric, and acetic acids); water absorption (immersion in boiling water for 5 hr); and visual inspec tions for dimension and imperfections, i.e., blisters, chips. STORAGE AND SHIPPING Following production and testing, vitrified clay pipe is stored on end in yards. It is shipped, as ordered, by rail or truck. Manufactures Vitrified clay pipe and products may be obtained from the following manufacturers. The list is not all-inclusive. American Vitrified Products Co., Cleveland, Ohio Can-Tex Industries, Inc., Mineral Wells, Tex., and Connelton. Ohio Denver Brick and Pipe Co., Denver, Colo. Grand Ledge Clay Product Co., Grand Ledge, Mich. International Pipe and Ceramics Corp., Parsippany, N. J. Iowa Clay Pipe Co., Des Moines, Iowa Lee Clay Products Co., Morehead, Ky. Logan Clay Products Co., Logan, Ohio Nalco Corp., Pittsburgh, Pa. Oconee Clay Products Div., Milledgeville, Ga. Pacific Clay Products Co., Los Angeles, Calif. Pomono Pipe Products Co., Greensboro, N. C. Robinson Clay Products Co., Akron, Ohio Streater Div., Clow Corp., Wheaton, 111. United States Concrete Pipe Co., Cleveland, Ohio Section 8--Concrete Pipe Concrete, actually hand-tamped natural cement, was used in the construction of Rome's Cloaca Maxima, or main sewer, which was constructed more than 2000 years ago and is still in use. The earliest recorded installation in this country was in 1842 in Mohawk, N. Y.28 Other installa tions were made more than 100 yean ago in San Francisco, Calif., and Utica, N. Y. The Concrete Pipe Handbook28 lists 99 cities with concrete sewer pipe systems more than 50 years old and 82 cities where the sewer systems contain more than 50 miles of concrete pipe of various sizes. CTD014847 SEPTEMBER 1967 | M 29 TABLE 16--DEIIGN CHARACTERISTICS OF NONREINFORCED CONCRETE PIPE Standard strength Extra strength (in.) Wall thickness (in.) Crushing strength* (Ib/lin It) Weight (ib/lin ft) Wall thickness (in.) Crushing strength* (Ib/lin ft) 4 9/16 1000 8.5 3/4 6 3/8 1100 17 8 3/4 1300 27 10 7/8 1400 37 12 1 1500 50 3/4 7/8 1 1-3/8 2000 2000 2000 2250 15 1-1/4 1750 78 1-5/8 2750 18 1-1/2 2000 105 2 3300 21 1-3/4 2250 159 2-1/2 3850 24 2-1/8 2400 203 3 4400 * Three-edge bearing test. Weight (Ib/lin ft) 13 20 31 42 68 100 150 230 315 According to the design criteria of the U. S. Navy Engi neering Facilities Command,23 precast concrete pipe "may be used where there is an indicated savings because of its low cost, adequate strength, and good joint capabilities." Precast concrete sewer pipe may be obtained in several shapes, many sizes, and with several types of joints. The choice of a particular type, shape, or joint depends on the use to which the pipe is to be put, the location and condi tions of installation and operation, and other engineering factors.-"' Design As is the case for all gravity-flow sewer pipe, internal pressure is not a design factor for concrete sewer pipe. With respect to external loads and supporting strengths, the de sign of concrete sewer pipe is based on consideration of trench loads and superimposed loads that are discussed in Part 2, Section 2 of this manual and in Manual of Practice No. 2.-' NONREINFORCED CONCRETE Plain concrete is used in sewers up to 24-in. in diameter. Sometimes termed "bell end" concrete pipe, it is of the bell and spigot type. There are several means of making up this bell and spigot type joint (see later discussion). Nonreinforced concrete pipe is manufactured in two grades, stan dard strength and extra strength, in accordance with ASTM Des. Cl4-65.30 This type of pipe is available in 3-ft lengths for 4- to 24-in. pipe diameters and in 4-ft lengths for pipe diameters of 10 to 24 in. In 21 and 24 in. diam., lengths of 6 and 7-1/2 ft are available. ASTM specifications place limits on the allowable variation in dimensions of laying length, internal diameter, barrel thickness, and depth, diameter, and wall thickness of the socket. Table 16 lists some of the impor tant physical characteristics of nonreinforced concrete sewer pipe. Under some conditions, and for different pipe sizes and pipe classes, there are limitations on the depth at which nonreinforced concrete may be safely buried in backfilled trenches. In general, the published limitations29 may be summarized as follows: For soil weighing 130 lb per cu ft, there is no limit on depth of cover for any size of extra-strength pipe placed on ordinary, first-class, or concrete-cradle bedding or for standard strength pipe placed on first-class or concretecradle bedding. Standard strength pipe in sizes of 18, 21, and 24 in. should have covers no deeper than 31, 21, and 18 ft respectively. For soil weighing 130 lb per cu ft, there is no limit on depth of cover for any size of extra-strength pipe laid on concrete cradles. For both strengths of pipe laid on ordinary or first class bedding, the allowable depth of cover for 130 lb per cu ft soil will vary with the pipe size and type; the better the bedding, the greater the allowable depth of cover, and usually, the larger the pipe diameter, the less the allow able depth of cover for the particular type of bedding. Data M 30 I WATER AND WASTES ENGINEERING in published tables29 are based on a trench width 16 in. greater than the outside diameter of the pipe. REINFORCED CONCRETE PIPE Reinforced concrete sewer pipe is manufactured in five classes, designated as I, II, III, IV, and V, in accordance with ASTM specifications. These classes have different strength requirements as indicated by the D-Load (Table 17), according to ASTM Des. C76-66T31. The strength test requirement under the three-edge bearing method may be expressed in terms of the D-load (test load in pounds per linear foot per foot of diameter) to produce a 0.01-in. crack, or in terms of this load and the D-load to produce the ultimate, multiplied by the internal diameter of the pipe in feet. Values for these strengths are shown in Table 17. Pipe within each of these class designations is manu factured in different sizes and three wall thicknesses (A, B, C) and has different reinforcement requirements. Pipe lengths of 4, 5, 8, and 12 ft are manufactured; the length depending to some extent on pipe size and on the manufac turer. Table 17 is a condensed listing of reinforced concrete pipe characteristics. Three compressive strengths, 4000, 5000, and 6000 psi, are shown. Reinforcement. Reinforcing steel is embedded in rein forced concrete pipe in such a manner that the concrete and the steel act together to give structural and supporting strength to the pipe. In some classes of pipe, for diameters less than 36 in., only one reinforcing cage is used (Fig. 15), the reinforcing being located 1 in. inside the inner surface of the pipe. In larger pipes of all classes, one of two meth ods of reinforcing may be used. In the first method, two reinforcing cages are used, one is 1 in. inside the inner sur face, the other 1 in. beneath the outside surface of the pipe (Fig. 15). As an alternative to the two-cage circular reinforcement design, a single elliptical reinforcing cage is placed within the circular pipe shell in such manner that the cage is no nearer the surface at any point than is specified. Pipe that is reinforced with an elliptical cage must be laid in such a position that the shorter axis of the ellipse is vertical, so that the pipe will provide its maximum supporting strength. A lifting hole is normally provided in the pipe to ensure that it will be laid in the proper position. Labels indicating "top" Fig. 15. Location of reinforcing steel in circular concrete sewer pipe left to right: single-cage, two-cage, elliptical. CTD014848 .. j i j t TABLE 17--DESIGN CHARACTERISTICS OF REINFORCED CONCRETE PIPE (Dtti gin* < minimun to maximum ringe) P load ____________Wall thickness (In.)____________ _____________Weight (Ih/f1) 0.01 in. Pipe ai2e crack Ultimate (in.) Wall A Wail B Wall Wall Wall C A8 Class 1 800 1200 Concrete strength 4000 psi 60-96 5-8 6-9 Concrete strength 5000 psi 102-108 8-1/2-9 9-1/2-10 Class II 1000 1500 Concrete strength 4000 psi 12-96 1-3/4--8 2-9 Concrete strength 5000 psi 102-108 8-1/2--9 9-1/2-10 Class III 1350 2000 Concrete strength 4000 psi 12-72 1-3/4--8 2-7 Concrete strength 5000 psi 78-108 6-1/2-9 8-1/2-10 Class IV 2000 3000 Concrete strength 4000 psi 12-66' 1-3/4--2-3/4* 2-5-l/2b Concrete strength 50000 psi 60-84- 6-7- Class V 3000 3750 Concrete strength 6000 psi 12-72k 2-5" b 1064-2710 4-3/4--9-3/4c 79-2710 10-1/4-10-3/4 4-3/4--8-3/4' 9-1/4-10-3/4 3-3/4--7-3/4- 3-3/4--7-3/4k 1295-3090 93-3090 Wall C 366-3020 4 Approximate; based on 150 tb per cu ft concrete. b Not manufactured, Available only from 36- to 96-in. diam. d 24- to 90-m. diam. < Available only from 36- to 84-m. diam. fModified or special designs above 30 in. for Wail A * Up to 30-in. diam. only. * Up to 54-in. diam. only. Available only from 24to66-in. diam. i 60 to 72 in. diam. in Wall B; 72 to 84 in. in Wall C. k 12- to 48-m. diam. in Wall B; 24 to 78 in. in Wall C. or "bottom" are sometimes used to show the short axis of the ellipse. The amount of reinforcing steel required depends on pipe size and necessary supporting strength. ASTM Des. C7666T" specifies the amounts of steel for each pipe size in each class of pipe and for each wall thickness.2 Pressure pipe. Where concrete pipe is to be used in sew age force mains or in siphons under pressure, the design en gineer on the project may find it desirable to specify con crete pressure pipe as used in water supply systems. Infor mation on this type of pipe was covered in considerable de tail in Manual of Practice No. 2.24 SHAPES OTHER THAN CIRCULAR Two pipe shapes other than circular are also manu factured; these are the arch-type and the elliptical. Arch-type concrete pipe. The cross-sectional shape of arch-type concrete pipe is an arch. The dimensions vary ac cording to pipe size and are specified by ASTM Des. C506-63T. Arch-type pipe is made in Classes II, III and IV, with 4000 psi strength concrete, except for 72- and 84-in. Class III pipe, which requires 5000 psi concrete. Table 18 shows the sizes available, with the accompany ing rise and span. The size is given as the diameter of a cir cular pipe of equivalent cross-sectional a-ea. Arch-type pipe is used where an economical solution is desired for a limited head application. This type of pipe is available in only a limited number of states. Elliptical pipe. Ellipticallv-shaped reinforced concrete pipe is manufactured in two types: horizontal-elliptical for low-head installations, and vertical-elliptical for high head applications. The horizontal-elliptical pipe is manufactured in Classes I to IV. the vertical-elliptical pipe in Classes II to VI. The latter type comes in compression strengths of 4000, 5000, and 6000 psi. depending on the pipe size. Both types are available in 4-, 6-. and 8-ft lengths; longer lengths may be obtained if specified. Pipe sizes are expressed in terms of their equivalent cir cular pipe diameters. The following data indicate some of the pertinent physical measurements of the minimum and maximum sizes available. The minimum size pipe is equiva lent in area (1.8 sq ft) to an 18-in. diam. circular pipe. It weighs approximately 200 lb per ft of length, and its rise versus span measurements are 14 x 23 in. for the horizon tal-vertical pipe and 23 X 14 in. for the vertical-horizontal pipe. The maximum size pipe is equivalent in area (118.6 sq ft) to a 144-in. diam. circular pipe; it weighs approximately 7300 lb per ft. and it has a rise versus span of approximate ly 129 x 193 in. for the horizontal pipe and 193 X 129 in. for the vertical pipe. Wall thickness in the smallest pipe size is 2-3/4 in. and in the largest pipe size is 13 in. Horizontal-elliptical pipe and vertical elliptical pipe of a given class have the same supporting strength as circular pipe of the same class. Calculation of hydraulic flow charac teristics are generally based on a Manning's n value of 0.012. Charts, diagrams, and nomograms available from the Bureau of Public Roads'52 show capacity, headwater depth, and head for pipes flowing full. There are also charts available from manufacturers, for both vertical and hori zontal types, showing the discharge in cubic feet per sec ond for various grade slopes, n-values, and equivalent pipe sizes. SAFETY FACTORS In the previous general discussion of design factors (Part 2, Section 2), it was pointed out that when designing sewers and calculating supporting strength required, a safety factor of 1.2 to 1.5 should be used. Concrete pipe manufacturers generally believe that a safety factor of 1.0 (using a 0.001in. crack load) is sufficient20 for reinforced concrete pipe because the specified "D-load" is a minimum for test samples, whereas the D-load on installed pipe is always higher. Furthermore, concrete pipe strength increases with age, thus offering a built-in safety factor. For most designs, a factor of 1.0 for a 0.01-in. crack load, results in a factor of at least 1.5 for the ultimate load. Characteristics Concrete is composed of a mixture of portland cement and aggregates (sand, gravel, or broken stone); it some times includes fly ash or air-entraining material in varying amounts. TABLE tl--DESI0N CHARACTERISTICS OF ARCH-TYPE REINFORCED CONCRETE PIPE Equtv. size* Water area Well thickness Min. rise (in.) (sq ft) (in.) (in.) Min. span (in.) 18 1.65 2-1/2 13-1/2 22 24 2.8 3 18 28-1/2 30 4.4 3-1/2 22-1/2 35-3/4 36 6.4 4 26-5/8 43-3/4 42 8.8 4-1/2 31-5/8 51-1/8 48 11.4 5 36 58-1/2 54 14.3 5-1/2 40 65 60 17.7 6 45 73 72 25.6 7 54 88 84 34.6 8 62 102 90 44.5 8-1/2 72 115 96 51.7 9 77-1/4 122 108 66.0 10 87-1/8 138 * Diameter of circular pipe with approximately equivalent cross-sec tional area. CTD014849 SEPTEMBER 1967 | M 31 Large diameter concrete sewer laid on selected fill in un sheeted trench. PHYSICAL CHARACTERISTICS Concrete pipe has a number of physical characteristics that make it useful in a sewer system. It is hard and dense and weighs from ISO to 165 lb per cu ft. The high density obtained by the methods used in manufacture and control of the ingredients in the mix ensure a high compressive strength--*000, 5000, or 6000 psi after 28 days. Tensile strength is considered to be one-tenth of the compressive strength. Abrasion resistance. Experience has shown that concrete pipe has long life, as witnessed by the number of communi ties with concrete sewer systems more than 50 years old. The durability evidenced by these case histories demon strates the resistance of concrete pipe to the normal abrasive action of domestic wastewaters and storm waters. Shrinkage and expansion. The shrinkage of good quality concrete stored in air ranges between 0.0002 and 0.0005 in. per in. Concrete stored in water will expand up to 0.002 in. per in. within a year. Thermal expansion is generally stated to be only 0.000006 in. per in. per degree Fahrenheit. This factor has no practical bearing on the installation of normal sewer systems. Absorption and permeability. ASTM specifications limit water absorption to 8 percent of the dry weight of the con crete pipe. Concrete's permeability to water is very small, and pipe lengths that show any water passing through the walls are rejected. This characteristic prevents infiltration through the pipe walls. To meet the standards presented in Part 2, Section 2, the several jointing methods available (see later discussion) practically eliminate infiltration at con necting joints. CHEMICAL CHARACTERISTICS Concrete is an alkaline material that is unaffected by water of normal or high pH. Concrete will react, however, with acids, whether they are in the soil surrounding the pipe, carried in the wastewater, or produced from the oxida tion of hydrogen sulfide within the sewers. When reasonable attention is given to protection against acid soil conditions, concrete pipe is durable in any type of soil. The denser the concrete, the more resistant it is to acidic soils. With respect to possible attack by acids on the interior surface of a concrete sewer, consideration need be given only to three simple factors. The pH of the wastewater M 32 I WATER AND WASTES ENGINEERING should be above 4.5; strongly acidic industrial wastes should be kept out of sewers; and conditions contributing to the production of hydrogen sulfide should be avoided. In sewer systems, hydrogen sulfide may be converted to sulfuric acid by a biological oxidation process; the resulting acid attacks the sewer. (This acidic attack is not peculiar tq concrete; some other sewer pipe materials are also attacked by acids in wastewaters.) There are several ways in which the formation of hydro gen sulfide can be prevented. By designing and installing the sewers to produce a velocity that will prevent stranding of solids on flat grades or sedimentation of organic matter in the sewers, and that will give the shortest possible flow time through the sewer; By keeping high-temperature and high-sulfate-content wastes out of the sewer system; By adding chemicals to the wastewater to prevent the growth of sulfate-splitting organisms; By providing flushing systems for sewers laid on flat grades; By installing ventilating systems to keep the concentra tion of hydrogen sulfide at a low value in the sewer atmo sphere. HYDRAULIC CHARACTERISTICS According to the Concrete Pipe Handbook,29 the Man ning formula is generally used in making flow calculations for concrete pipe. The Handbook recommends that the n values be 0.013 for sanitary sewer pipes, and 0.010, 0.011, or 0.012 for concrete storm sewer pipe. The value for sani tary sewers is conservative and takes into account bends, wyes, tees, connections, and operating conditions. The storm sewer values are based on straight, well-graded pipe flowing full (0.010) and flowing partly full (0.011). Manufacture The project design engineer sometimes will specify the characteristics needed for the concrete in a particular sewer, but generally, the manufacturer is more familiar with local cements and is more qualified to select the materials and design the mix. All processes begin with the design of the mix or the combination of ingredients. MATERIALS As indicated previously, concrete pipe is made from "an extremely dry mix of cement, sand, and gravel or broken stone and water,-with or without additions such as fly ash and/or air-entraining agents .. ."* The design of the concrete mix is fairly standard, but in dividual manufacturers may adapt these designs to fit their own operations and product characteristics. Whatever the individual plant design mixes used, the final product de pends on these factors: suitability of materials, accurate measurement of ingredients, thorough mixing, proper water-to-cemeni ratio, proper placement of mix in forms, and adequate curing and testing to ensure strength, durabil ity, and impermeability of the resulting pipe. According to the Portland Cement Association,29 "De signing a concrete mix . . . consists of selecting the watercement ratio that will produce concrete of the desired resis tance to exposure and the required strength, and finding the most suitable combination of aggregates, which will give the necessary workability when mixed with portland cement and water in this ratio." The design of the concrete mix is generally done by the manufacturer and not by the project design engineer. PROCESSES The four most common methods of concrete pipe manu facture are briefly described below. Cast and vibrated pipe. Steel forms of a size to produce the desired inside pipe diameters and wall thickness are CTD014850 filled with the desired concrete mix, which is compacted by vibration (using either air or electric vibrators) applied both outside the form and to the concrete mix itself. The vi bration expels all entrapped air, gives the concrete the de sired density, and imparts a smooth finish to the inside and outside walls of the pipe. After vibration, the form is al lowed to stand until the concrete sets. When the form is stripped away, the pipe is cured for the time specified to produce the strength class desired. This process can be used for both nonreinforced and reinforced sewer pipe. Packerhead process. This method for manufacturing nonreinforced and reinforced concrete pipe utilizes a ma chine with a revolving "packerhead" that continuously packs the dry mix in the form from bottom to top as the form is filled with the mix. The mix is so dry and is packed under so much pressure that the green pipe can be removed from the form after the packing operation is completed. The green pipe is sent to curing immediately, where it is cured in the vertical position. The packerhead process produces the density and smooth surfaces desired in the final product. Tamped pipe process. This method for manufacturing nonreinforced pipe utilizes a form in which the dry mix is tamped by wooded hammers fitted with steel shoes that strike the surface of the mix 500 to 600 times a minute as the mix is continuously added to the form. In this process, the inside core remains stationary while the outside form re volves. When the form is filled with the tamped mix, the green pipe is removed immediately and placed in the curing room. It is the tamping of the mix that ensures the desired density and smoothness of the inside wall. According to some manufacturers, this process is becoming obsolete. Centrifugal process. Pipe manufacture by the centrifugal process involves forms rotating at high speed, with the con crete added in such a manner that it is compacted against the form, and the excess water is literally squeezed out. This method is used in the manufacture of reinforced concrete pipe. The mold consists of a steel cylinder in which the steel reinforcing cage is placed and secured. The smoothness of the inside of the pipe is obtained by the high centrifugal force produced during the rotation of the form. This is a simplifed description of the centrifugal process, of which there are a number of patented methods. The manufacture of centrifugally produced pressure pipe was described in Manual of Practice No. 2.24 Curing. Concrete sewer pipe may be cured by either the steam or water process or by a sealing membrane. These methods are described in Manual of Practice No 2.24 Testing Possibly the most important factor in the production of concrete sewer pipe is the testing to which samples of pro duction are subjected. Acceptance or rejection of pipe is based on the tests that are specified in ASTM Des. C-14 for nonreinforced pipe and ASTM Des. C-76 for reinforced concrete pipe. The properties of both types of pipe tested in clude: crushing strength (three-edge bearing test), absorp tion. sizes and dimensions, permeability, defects and imper fections. and finish of ends. Nonreinforced concrete pipe is subjected to a hydrostatic test of 10 psi for 10 min to deter mine leakage The concrete in reinforced concrete pipe also must pass a compression test. All these tests are made in ac cordance with the appropriate ASTM specifications. Liners and linings Concrete sewer pipe that may be subjected to abnormal conditions in operation, such as acids, gritty material, or hy drogen sulfide, may be lined to protect the inside surface of the pipe. A good lining should have the following characteristics: resistance to acids, chemicals, water, and abrasion: assured adherence to the pipe's interior surface: imperviousness; Fig. 16. Cross section, exaggerated, of integral-type epoxy lining in concrete pipe. ample thickness; and resistance to attack by biological or ganisms. The major methods of applying such linings in clude integral lining, insertion of plastic liners, lining in place, and liquid application. INTEGRAL COATING In a patented process, an integral aggregate-filled coal tar epoxy lining is produced on the inner surface of the pipe. The epoxy lining, containing selected silica aggregates, is applied to an average thickness of 100 mils on the interior of uncured, dry-mix, machine-made concrete pipe (18 to 72 in. up to 12 ft lengths) immediately after the pipe is manu factured. The pipe is cured after the application of the lin ing. During the curing process, the lining develops a physi cal-chemical molecular adhesion with the concrete surface to become an integral part of the concrete wall. An exager ated cross-section of lined pipe is shown in Fig. 16. Laboratory tests indicate that this lining resists acids, abrasion, strong chemical solutions, and hydrogen sulfide. Manufacturing tests have been made of its adhesive quali ties and its resistance to impact, hydrostatic pressure, and infiltration under pressures up to 50 psi. The process was developed in 1962, and pipe of this type has been installed in many sizes at a number of sites since that time. PLASTIC LINER A liner consisting of a high polymer vinyl chloride resin is molded under high temperature and pressure to form a dense and impervious material. This liner can be cast into any concrete pipe that is formed on an inner mold. Its de sign is shown in the exaggerated sketch in Fig. 17. Joints be tween sections of the liner, from pipe section to pipe section, are made by heat-welding the material to itself to obtain a continuous impermeable lining. Another system employing a PVC sheet and a specially designed adhesive and application method, may be used on concrete pipe manufactured by any process. FIELD APPLIED EPOXY Epoxy material containing finely divided silica is applied to new pipe sections either in the field or after installation using a lining process similar to that used for cement lining of water mains in place. The method is described in some detail in Part 2, Section 13 of this manual. LIQUID APPLICATION The interior or exterior of concrete pipe may be painted with bitumastic, coal-tar epoxy, or other resistant substance, either at the manufacturing site or at the project site. SEPTEMBER 1967 | M 33 CTD014851 Fig. 17. Cross section, exaggerated, of plastic liner for con crete pipe. Joints and fittings Various types of joints are available for connecting con crete pipe sections, and the type of joint used often depends on the ground water conditions, pipe size, the manufacturer, and whether the pipe is reinforced or nonreinforced. The principal types of joints are bell and spigot, tongue and groove, modified tongue and groove (with a reinforced modified bell), concrete collar, single rubber ring gasket, and external band. Methods of making joints will be dis cussed in Part 3 of this manual. Fittings of all types, including bends, wyes, tees, connec tions, and specials, are available in all sizes. Cast-in-place concrete pipe Concrete sewers cast in-place involve engineering design formulas and calculations. Different shapes involve dif ferent engineering design approaches. Principles of design for such sewers may be found in standard reference texts5 10 50'2C and will not be covered in this manual. Manufacturers Manufactured concrete pipe, joints, and fittings may be obtained from the following manufacturers; the list is not necessarily all-inclusive. For a complete list, consult the American Concrete Pipe Assn. American Pipe & Construction Co., Monterey Park, Calif. The Cretex Co., Inc., Elk River, Minn. Gifford-Hill Pipe Co.. Dallas, Tex. Hydro Conduit Corp.. Denver, Colo. International Pipe & Ceramics Corp., Parsippany, N. J. Price Brothers Co.. Dayton, Ohio United Concrete Pipe Corp.. Birmingham, La. United States Concrete Pipe Co.. Cleveland. Ohio Vulcan Materials Co., Atlanta. Ga. Specially lined pipe, as described previously, or epoxy lining-in-place may be obtained from the following com panies: Epoxy lining-in-place; Centriline Corp.. Div. of Ray mond International. Inc.. New York. N. Y. Integral lining; U. S. Steel Chemicals. Div. of U. S. Steel Corp.. Pittsburgh, Pa. Plastic linings are manufactured by Amercoat Corp., Brea. Calif., but are applied by the pipe producer. M 34 I WATER AND WASTES ENGINEERING Section 9--Plastic and Plastic Lined Pipe Until recently, the use of plastic pipe in sewer systems was limited to building sewers, house sewers, and force mains, primarily because the largest size available was 6 in. in diameter. In about 1965, a specially designed plastic pipe, termed truss pipe, was, introduced in sizes of 8-, 10-, 12-, and 15-in. diam. In 1967, a British manufacturer an nounced the production of extruded polyvinyl chloride pipe (PVC) in diameters up to 16 in., with the future possibility of producing 20-, 24-, and 30-in. pipe. These developments undoubtedly will lead to the wider use of plastic pipe for sewers. ABS, PE, and PVC pipe The U. S. Department of Commerce has issued two com mercial standards for plastic drain, waste, and vent pipe and fittings (CS 270-67 for ABS and 272-65 for PVC pipe) and one for sewer and drain pipe (CS 228-61 for styrene-rub ber plastic). As the use of plastic pipe for sewers increases, there may be standards developed specifically for plastic sewer pipe of various compositions. Information on the design, specifications, manufacture, and testing of plastic pipe for water systems may be found in Manual of Practice No. 2.24 Manufacture of plastic sewer pipe is similar. In addition to the types of pipe used for water systems and/or drain, waste, and vent systems, there are two types of plastic pipe designed for wastewater use: styrene-rubber plastic pipe, and truss-type plastic pipe. Styrene-rubber plastic pipe This type of pipe is an extruded product and is available in 10-ft lengths. Four sizes are produced, each with a crush ing strength of 1000 lb per lin ft. The dimensional charac teristics of this type of pipe, as given in CS-228-61, are as follows: Pipe size (in.) 2 3 4 6 Wall thick ness (in.) 0.073 0.100 0.125 0.183 Weight (Ib/ft) 0.25 0.49 0.78 0.67 Fig. 18. Cross section of truss-type ABS plastic pipe. CTD014852 TABLE l--DATA ON TRUSS-TYPE PLASTIC PIPE Pipe size Regular strength (in.) 8 10 12 16 Extra strength (In.) 4 6 Length (ft) 6-1/4, 12-1/2 6-1/4, 12-1/2 6-1/4, 12-1/2 6-1/4, 12-1/2 6-1/4, 12-1/2 6-1/4,12-1/2 Weight (Ib/lin ft) 8 11 15 26 The pipe has a tensile strength of 3100 psi, an impact strength of 3.2 ft-lb per in. notch, and an elongation of 17 percent. It is resistant to acids, detergents, caustics, and or dinary domestic wastewater. Jointing is done by the solvent-weld method to form leakproof and rootproof joints. All types of fittings are available. Plastic truss pipe This type of plastic pipe (Fig. 18) consists of two inter connected walls of acrylonitrile-butadiene-styrene (ABS) resin tied together by a truss of the same material, with the voids filled with lightweight concrete. DESIGN The lightweight concrete in the voids of truss-type plas tic pipe helps to carry the compressive load and provides lateral support for the truss members. Tensile stresses are carried by the pipe wall. Either of two methods may be used in calculating the necessary resistance or supporting strength for backfill load ing: the deflection design method or the ring compression method.33 Tests using the latter design method indicate that the maximum backfill depth should be 48 ft, based on a given wall strength, a soil weight of 100 lb per cu ft, and a safety factor of 4.0. The maximum recommended permissible design deflec tion is 5 percent in a period of 12 months. Field tests indi cate that where bedding is good, the maximum deflection noted was 2 percent in 12 months. CHARACTERISTICS Truss-type plastic pipe is relatively light in weight and, because of its composition, is quite durable for sewer in stallations. It has a high resistance to abrasion, freezing, and thawing, and is not affected structurally at temperatures up to 130 F. Thermal expansion is not significant over normal installation ranges. This type of pipe is chemically resistant to hydrogen sulfide and acids in concentrations up to 5 per cent. Minimum specification (ASTM D-18617) for crushing strength is 1500 lb per lin ft, but tests on 8-in. pipe show that between 60 and 130 F, the crushing strength ranges from 2100 to 1650 lb per lin ft. Good hydraulic flow characteristics result from the smooth surface of the interior wall of the pipe. As produced, this tvpe of pipe is stated to have a Manning n value of 0.010. MANUFACTURE AND TESTING Truss-type plastic pipe is made by an extrusion process that forms both the walls and the truss arrangement simul taneously. Data on pipe sizes and weights are given in Ta ble 19. Jointing is accomplished by chemical (solvent) welding to produce a sewer that is leakproof, and resists root penetration, and infiltration. All types of fittings are avail able. Plastic pipe (15-in.) for sewer line in New York State. Laboratory tests made on pipe after manufacture include beam tests and impact tests. By specifications of the manu facturer, truss pipe must show no leakage after sustaining a 1-in. deflection for 24 hr with a 10-ft internal water head. The required spans for the flexural test are 82, 90, 96, and 110 in. for pipe diameters of 8, 10, 12, and 15 in., respec tively. Beam tests on 8-in. pipe show deflections of 1, 2, or 3 in. in a 10-ft span, with respective loads of 870, 1460, and 1900 lb. Plastic-lined pipe Steel pipe that has a plastic lining may be considered as plastic lined steel pipe; it also may be considered as steel armored plastic pipe. In this manual, this type of pipe is termed plastic-lined pipe. The greatest use of plastic-lined pipe is in handling cor rosive chemicals. Currently, the most important application of plastic-lined pipe in the wastewater field is in the disposal of chemical wastes into underground wells. DESIGN AND MANUFACTURE Plastic-lined steel pipe is produced with three types of extruded liners, namely, saran, Penton, and polypropylene. These liners are tough and stabilized; they range in thick ness from 5/32 to 9/32 in. They are locked in place on the inside of the steel pipe walls by a force of several thousand pounds per square inch. The result is a thick-walled pipe with a heavy steel shell, the two layers being virtually mono lithic. The pipe thus produced is suitable for use at tem peratures from -20 to 200 F or higher. Pipe is available in sizes from 1 to 8 in., weighing from 2.4 to 28.6 lb per ft; it is made in 10 ft lengths. In another manufacturing process, a special polyethylene co-polymer is bonded to both the inside and outside of steel pipe. This type of pipe is produced in approximately 30-ft lengths, with coatings of plastic 30 mils thick. Pipe sizes (diameters) available include 2, 3, 4, 6, and 8 in. The weight of this pipe ranges from 1.73 to 10.7 lb per ft. Joints are couplings or flanges. The method for lining concrete pipe with plastic was previously described (Part 2, Section 8). Manufacturers Companies that produce acrylonitrile-butadiene-styrene (ABS), polyethylene (PE), polyvinyl chloride (PVC), or CTD014853 SEPTEMBER 1967 | M 35 styrene rubber plastic sewer pipe include the following: (All the companies listed do not necessarily produce all types of plastic pipes.) Anesite Div., Clow Corp., Chicago, 111. Can-Tex Industries, Inc., Mineral Wells, Tex. Carlon Products Corp., Aurora, Ohio Celanese Plastics Co., Columbus, Ohio Dan-dee Products Corp., Union City, Calif. Ethyl Corp., Visqueen Div., Baton Rouge, La. Evanite Plastic Co., Carrolton, Ohio Flintkote Corp., Orangeburg, N. Y. Gering Plastics Co., Div. of Monsanto, Kenilworth, N. J. Haveg Industries, Inc., Amco Pipe, Wilmington, Del. Johns-Manville Corp., New York, N. Y. U. S. Pipe & Foundry Co., Birmingham, Ala. Companies that produce plastic-lined pipe or plastic liners include the following: Amercoat Corp., Brea, Calif. Dow Chemical Corp., Midland, Mich. International Protected Metals, Inc., South Plainfield, N. J. Companies that produce truss-type plastic pipe include: Armco Steel Corp., Metal Products Div., Middletown, Ohio Robinson Clay Product Co., Akron, Ohio Section 10--Reinforced Resin Pipe For the purposes of this manual, fiberglass reinforced pipe is not defined as plastic pipe because the composition and methods of manufacture differ from those of the plastic pipe discussed in the previous section. Commercial products on the market carry registered trade names that do not in dicate the composition of the pipe. At least two major types of reinforced resin piper are available commercially. Reinforced epoxy or polyester plastic This type of pipe, sometimes termed simply GRP (glassreinforced pipe), is composed of fiberglass reinforced epoxy resin or polyvinyl ester. At least one commercial product is available in three classes. When epoxy resin is used, it meets ASTM Spec. Des. 1763-63. The pipe is tested for various characteristics in accordance with several applicable ASTM specifications. Each grade of pipe has a different temperature range resistance; the thermal expansion coeffi cient of the pipe in diameters from 4 to 12 in. is approxi mately 9 x 10- in. per in. per degree F. The pipe has a low hydraulic-flow friction coefficient; the Hazen-Williams C-value being stated by one manufacturer as 150. Glass-reinforced piping is available in 15 and 20 ft lengths and in diameters from 2 to 24 in., but larger di ameters can be obtained for special applications. In one process of manufacture, the pipe is built up by laminations, as follows: Inner surface--0.01 to 0.02 in. smooth resin-rich in terior, reinforced with surfacing mat or veiling. Next interior layer--0.1 in. (minimum) chemical-re sistant layer, 25 to 30 percent glass by weight. Remaining interior layers--varied thickness of glass and resin to obtain the required laminate strength. Exterior surface--resin-rich surface, reinforced with a surfacing mat. This type of pipe has high corrosion resistance but not necessarily abrasion resistance. The corrosion resistance is provided by the resin; the strength by the fiberglass. Best corrosion-resistance/strength characteristics are obtained M 36 I WATER AND WASTES ENGINEERING TABLE 10--DATA ON GLASS-REINFORCED PIPE* Class 2025 Size (in.)** Wall thickness (in.) Weight (lb/ft) 2-12 0.2-0.25 0.83-6.70 Collapse pressure at 80"F (psi) Axial load pressure at 225-6 80F (psi) 3000-18,000 Internal pressure resistance at 200F (psi) 200-130 Class 2530 2-12 0.25-0.3 1.25-8.0 350-10 4000-25,000 300-160 Class 1040 2-12 0.3-0.4 1.4-10.4 400-25 4500-37,000 400-240 * Class 2025 is suitable for use at temperatures up to 200*F, Classes 2530 and 3040 at temperatures up to 300F. ** Nominal inside pipe diameters available are: 2, 2-1/2, 3. 4, 6, 8, 10, and 12 in. TABLE 11--DATA ON REINFORCED PLASTIC MORTAR PIPE Pips size (In.) 8 10 12 15 18 21 24 27 30 33 36 39 42 48 Weight (Ib/ft) Low head (125 ft) 5.5 7.0 9.5 13.0 15.5 19.0 23.0 28.0 35.5 43.0 47.5 60.0 69.5 90.5 High head (200 ft) 5.5 7.0 9.0 10.5 15.0 20.0 22.0 25.5 31.0 37.5 44.5 52.5 61.0 80.0 with 25 to 40 percent glass and 75 to 60 percent resin. Coupling joints may be threaded, solvent-welded, or made with resin coatings. This type of pipe has been found useful in industrial wastes systems, particularly for deep-well disposal of indus trial wastes. Table 20 lists the characteristics of three classes of pipe produced by one manufacturer. Reinforced plastic-mortar pipe Reinforced plastic mortar pipe has a composite structure (Fig. 19) of synthetic polyester and sand mortar reinforced with continuous glass fibers. This type of pipe is manufactured in two classes: low head (125 ft), and high head (200 ft). Because the high head pipe will be subjected to higher internal pressures, it contains a larger percentage of reinforcing glass filaments and less sand filter; consequently it weighs less per foot (Table 21). Wall thickness for the low head pipe ranges from a nominal 0.2 in. for 8-in diam. pipe to about 0.4 in. for the 48-in. pipe size. The wall thickness of high head pipe is similar to that of low-head pipe but in some cases it may be slightly less. Nominal weights per foot are shown in Table 21. This type of pipe is manufactured in standard 10 ft laying lengths, but 20 ft lengths may be obtained. No pub lished data are available at this time on the pipe's support ing strength for backfill loads in trenches. The material in this type of pipe will not react with the acids and chemicals normally encountered in domestic or industrial wastew aters or with corrosive soils. It is also resistant to electrolytic or galvanic corrosion and hydrogen sulfide. The internal sur face of this pipe is extremely smooth and for hydraulic flow design calculations, the manufacturer recommends a Man ning's n value of 0.009. CTDO14854 Fig. 19. Reinforced plastic mortar pipe composition. Joints are of the bell and spigot type sealed with a fully contained round rubber gasket that produces joint tightness capable of preventing leakage and resisting root entrance. This type of pipe has been used for new sewer lines and as a liner for deteriorated pipelines. When used as a liner, the reinforced plastic mortar pipe is pulled inside the old pipeline. Manufacturers Glass-reinforced pipe is manufactured by: Amercoat Corp., Brea, Calif. Ceilcote Co., Berea, Ohio Fibercast Co., Div. of Youngstown Sheet and Tube Co., Sand Springs, Okla. Reinforced-plastic-mortar pipe is manufactured by: United Technology Center, Div. of United Aircraft Corp., Sunnyvale, Calif. Section 11--Steel Pipe Steel pipe is used for sewers in which its characteristics of lightness, imperviousness, flexibility, and resistance to inter nal and external pressures are applicable. It has found spe cial application in locations where shock, ground move ment, and external pressures may occur. Because of its flex ibility, steel pipe will distribute deflection, buckling, or flat tening loads in such a manner as to resist additional distor tion without failing. Two types of steel pipe are available for use in sewer construction, smooth wall and corrugated. Smooth-wall steel pipe Smooth-wall steel pipe is used for above-ground installa tions, for force main or sewers operating under pressure, Ten-foot section of reinforced plastic mortar pipe for sewer drain near Fresno, Calif. and for sewer lines suspended under bridges. In some in stances, the pipe used for these applications is the same type as that used for water systems; in others, a pressure sewer pipe is used. The design, manufacture, lining, jointing, and testing of steel water pipe is covered in Manual of Practice No. 2.24 A description of three major installations will serve here to show how such pipe is used in the wastewater field. One notable example of a steel pipe used in a wastewater system is that which carries treated sewage from Baltimore, Md., to the Sparrows Point plant of the Bethlehem Steel Corp., where the activated sludge effluent is used as cooling water. A 60-in diam. steel line was constructed in 1942, and a 23,800-ft long, 96-in. diam. line in 1955. Total capacity of the two lines is 190 mgd. The larger line was laid in 40-ft sections welded together in the field. This pipe has wall thicknesses of 1/2, 9/16, and 5/8 in.; the three thicknesses being selected to meet the varying depth of cover conditions encountered. The pipe sections were coal-tar enameled, in side and out, and wrapped with 15 lb felt. Joints were coated and wrapped after welding. Another notable steel pipe installation is the 10-mile long, 28-in. line that canies a treated industrial waste effluent from the Toms River Chemical Corp. in New Jersey to the Atlantic Ocean. The ocean outfall section is 3500 ft long. The inside of this pipe is coated with coal-tar enamel 3/32 in. thick; the outside is also coal-tar-enamel coated and wrapped with felt. The outside of the outfall section was factory-coated with a 1/2-in. layer of asphalt. Before instal lation, the joints were welded and coated, and the ocean outfall section was wrapped with wire netting and sprayed with a 2-in. coating of high density concrete. As a further protection against electrolytic corrosion, a continuous zincribbon anode was installed inside the entire pipe. A third interesting steel pipe sewer is the 2-mile welded steel pipe, 18 to 36 in., installed as part of the influent sewer to the High Point, N. C., wastewater treatment works. Much of this pipe was installed on piers 8 to 35 ft above ground level. Pressure sewer pipe Pressure sewer pipe is a composite pipe consisting of smooth-wall welded steel pipe that is coated inside and out side and wrapped outside. It may be used when the project requires pressure sewer construction. DESIGN This type of pipe has been designed for various combina tions of internal pressures and external backfill and liveload pressures. The internal pressure design is based on a unit stress in the pipe that does not exceed 50 percent of the minimum yield strength at maximum operating pressures (static head or gradient flow conditions, whichever is greater) .*4 External load design is based on computed ring deflection that does not exceed 2 percent of diameter.28 CHARACTERISTICS Steel pressure sewer pipe has characteristics of strength, resiliency, and ductility, which result from the composition of the metal. Careful lining and coating ensure a long life. Physical characteristics. The product characteristics re sulting from the design of the pipe cause this type of pipe to have a high beam strength. It is able to resist external loads caused by uneven bedding, unequal settling of fill, or acci dental undermining of the pipe. Both types of lining (coal-tar enamel and cement-mor tar) have been shown by experience in Los Angeles. New Orleans, and elsewhere to have good resistance to abrasion and scour in force-main service. Chemical characteristics. Coal-tar enamel linings in steel pressure sewer pipe are chemically inert and resistant to municipal and industrial wastes, hydrogen sulfide, acids and alkalies. Cement-mortar provides good protection for the M 37SEPTEMBER 1967 | CTD014855 TABLE B-OATA ON STEEL PRESSURE-SEWER PIPE OomotHMrtir Snd Thicknats of Nominal mortar (In.) 14 16 18 20 22 24 28 30 32 34 36 (In.)' 5/16 5/15 5/16 5/16 5/16 3/8 3/8 3/8 3/8 3/8 3/8 Outsldo (In.) 15.0 17.0 19.0 21.0 23.0 25.375 29.375 31.375 33.375 35.375 37.375 Cla_s_t 200 40.25 47.95 53.07 62.04 77.34 96.78 106.41 113.03 125.45 137.43 Class 225 34.35 42.82 49.73 56.58 65.65 81.59 104.16 116.59 123.95 143.13 149.78 Class 2S0 35.13 44.41 51.12 61.62 69.50 85.82 109.07 120.20 134.94 154.59 161.79 Pipa walflht (Ib/lin ft) Class 27$ Class 200 Class 225 37.66 45.65 54.08 64.90 39.08 48.30 57.24 66.86 40.18 49.71 60.39 70.13 73.33 76.92 80.75 89.79 96.92 102.19 118.57 128.04 128.04 126.75 145.74 154.59 136.89 156.53 166.04 146.98 173.77 Class ISO 42.53 52.35 63.35 73.62 88.15 110.34 137.50 Clast S7S 43.78 53.93 66.49 76.01 88.15 110.34 Clast 400 45.04 56.96 66.49 80.00 Note: Coal-tar enamel lined pipe is available in 8% through 96-in. diam., in all required pressure classes, in lengths to meet design requirements up to 50 ft. steel pipe against normal municipal and industrial wastewa ters. It does not protect against attack by wastes of low pH, or by septic wastes, where hydrogen sulfide conditions de velop. The outside coating and wrapping protect against acid soil conditions. Hydraulic characteristics. Because steel pressure pipe is lined with coal-tar enamel or cement mortar, in accordance with the specifications for lining steel water pipe,24 it has good hydraulic flow characteristics, with a Hazen-Williams C-value of 140+ for new pipe. In flow calculations, many designers use a C value of 135 for this type of pipe. manufacture and testing Steel pressure sewer pipe is manufactured in the same manner as steel water pipe.24 After the pipe lengths are produced, they are lined, either by centrifugally spun coal tar enamel or by centrifugally applied cement-mortar, to provide a dense lining for sewer service. Several layers make up the protective coatings. Table 22 shows data on di mensions and weights of available sizes of pressure-sewer pipe in different classes. The class numbers represent the working pressure (pounds per square inch) for which the pipe is designed, and the data for cement-mortar lined pipe. Sizes from 8-5/8 through 12-in. diam. are available only with coal tar enamel linings. Larger sizes are normally supplied with either cement-mortar linings or coal tar enam el linings. Regardless of the lining material used, the effec tive internal diameter is, for all practical purposes, equal to the nominal series given in Table 22. JOINTS Steel pressure-sewer pipe may be welded at the joints, if specifications require. For this type of jointing, the pipe ends may be square, beveled, or slip bell as specified. This type of pipe may also be joined by Dresser or other me chanical couplings. Steel pressure-sewer pipe is generally furnished with an O-ring-type. rubber-gasketed bell and spigot joint that is self centering, flexible, and watertight under normal conditions of expansion, contraction, external live and earth load, settlement and vibration (see Fig. 20). This joint, termed a slab-joint, is designed to withstand internal pressures up to 400 psi and external hydrostatic pressures of more than 100 ft head. Both bell and spigot ends are formed integrally during manufacture of the pipe. This type of joint employs metal-to-metal contact of spigot against the inside of the barrel to provide support for the pipe barrel against imposed externa! loads. With this type of joint, a deflection of 3 degrees (depending on pipe size) is possible in laying. If the project engineer desires to eliminate the discontinu- M 38 I WATER AND WASTES ENGINEERING ity of pipe interior at the joint, the pipe can be lined in place in the field, with cement-mortar or cold applied mastics, either during or after assembly of the line. Fittings that meet AWWA Standard C-208 are available for whatever purpose desired. Corrugated steel pipe Corrugated steel pipe is produced in two types: contin uous seam and riveted. Riveted corrugated pipe is produced in two ways, depending on pipe size. In smaller diameters, the pipe is formed from a metal sheet welded at one seam. In larger sizes, welded pipe is spiral welded. Large diameter riveted corrugated pipe is formed in the field by riveting together curved sheets to yield the desired diameter. This type of pipe is termed mul tiplate. Corrugated pipe has found wide application for culverts and for drainage. Multiplate pipe in large sizes is used for this purpose. The usefulness of corrugated pipe for wastewater sewer installations is diminished by its relatively high roughness coefficient. Hydraulic flow characteristics may be improved either by lining the invert or lining the whole internal surface of the pipe. The pipe may also be lined in place, either with a cement-mortar or an epoxy lin ing. One interesting application of corrugated steel pipe is the placing of a sanitary sewer in a larger steel pipe storm drain as a means of separating domestic wastes from storm water. CTD014856 Steel pipeline (96-in.) carries effluent from Baltimore acti vated sludge plant 4-1/2 in. to steel plant for use as cooling water. DESIGN When steel pipe is corrugated, its strength and ability to resist bending under superimposed loads is increased. Whether corrugated pipe is welded or riveted, the design be gins with selection of the thickness or gage of the sheet metal. There are two ways of determining the gage of metal to be used for a particular installation. The first makes use of published tables that have been developed from standards set by the American Association of State Highway Officials (AASHO). These tables are based on gross loadings of 20, 15, or 10 tons with and without live loads. Tables of this type are available from manufacturers of corrugated steel pipe. The second procedure is known as the ring compres sion method of design.83 Ring compression analysis. By mathematically analyzing corrugated steel pipe behavior in a backfilled trench, it is possible to calculate the required gage of the metal without relying on tables. The method is based on the principle that corrugated steel pipe installed in a well-compacted backfill acts as a thin ring in compression, with uniformly distributed forces acting along the periphery of the structure. The calculation is expressed mathematically as where: C = PR Eq. 16 C = compression in the ring (lb per lin ft) P = external radial pressure (lb per sq ft) R = radius at point of measure (ft) Compression is assumed to be constant throughout the ring (neglecting friction and bending). Computation steps. There are six steps involved in de signing a pipe structure by this method, as follows: Dead load. Using a value of 100 lb per cu ft as the weight of the backfill, P from Eq. 16 becomes 100 lb per sq ft. Dead load therefore is where: DL = HC X P Eq. 17 DL = dead load (lb per sq ft) HC = depth of cover (ft) Live load. Handbooks and published tables provide data on live loads from trucks of different weight. The method for calculating live loads can be the same as that used in the design of cast iron pipe, as described in Manual of Practice No. 2 (page M15).24 Diagrams and tables for truck loads are given in AWWA Handbook H-l.3r' Compression ring. The dead load is added to the live load, and the sum is multiplied by one half the span (ft) or by the pipe radius (ft). Cage determination. The compression value is multiplied by a safety factor of three for corrugated pipe or by a factor of four for multiplate structures. Then the proper gage is selected from a manufacturer's table of seam strengths. Flexibility. The flexibility is checked to ensure that the pipe structure will have adequate moment strength for han dling and for resisting the shock of backfilling and the ulti mate backfill load. The following formula has been recom mended for calculating the maximum flexibility factor:30 D2 FF = Ef Et 18 where: FF = flexibility factor D = pipe diameter (in.) '53A I = moment of inertia of wall (in.) E = modulus of elasticity (psi) Minimum cover. In calculating minimum cover, the as sumption is -made that a round pipe becomes a compression ring with top dead load balanced at a cover of approximate ly one-fourth the diameter. During backfilling, the pipe must have a great enough bending resistance to withstand compaction pressures. Because of this bending strength, the minimum cover required may be reduced to one-eighth in stead of one-fourth the diameter, but the minimum cover should never be less than 1 ft. CHARACTERISTICS Corrugated steel pipe has both strength and flexibility, and, because of its configuration (corrugations), it distrib utes the load upon it more or less uniformly around its en tire periphery. Unit pressure at top and bottom is as little as one-third that on a rigid pipe structure; this fact has a direct bearing on the life of the pipe. Under normal conditions, coated corrugated pipe will have an acceptable durability. Unless coated, this type of pipe is subject to attack by wastes of low pH, hydrogen sulfide, and other corrosive materials. Coatings and linings will be discussed later. The hydraulic flow characteristics of corrugated pipe de pend on whether or not the interior of the pipe is coated and lined. For example, in sewer design computations using Manning's formula, the following n-values are recommend ed: Uncoated, 1/2-in. corrugations Asphalt coated and 25 percent paved Smooth asphaltic lining 0.024 to 0.026 0.021 to 0.023 0.012 to 0.015 MANUFACTURE The gage of metal used is no. 16 for pipe up to 21 in. in diameter. Lower gage numbers (heavier plate) are used for pipes 84-in. in diameter or larger. Copper-steel alloy is used in some types of pipe. In forming corrugated pipe, sheets of steel of proper size for the required diameter are rolled and formed into corru gated sections, then riveted along the longitudinal and cir cumferential seams in the valleys of the corrugations. Multi plate pipe sheets are formed to the proper radius. Helical pipe is lock seamed into an integral unit of the desired length. In this type of pipe, the corrugations are formed diagonally around the pipe instead of at right angles SEPTEMBER 1S67 | M 39 CTD014857 TABLE 11--RANGE OF WEIGHTS OF CORRUGATED STEEL PIPE Pip* type Standard (galvanized) Fully asphalt coated Half coated, invert paved Fully coated, invert paved IS gaga 5.8 7.0 8.0 9.0 Weight (Ib/ft)______ 36-In., 12 gage H-In., s gg 51.0 59.5 212 231 63.2 241.5 70.7 251 GALVANIZED OR ASBESTOS-BONDED ASPHALT CORRUGATED STEEL PIPE j LINING SMOOTH INTERIOR SURFACE ASPHALT------ f EXTERIOR COATING Fig. 21. Procedure for providing smooth interior surface in corrugated steel pipe. to the length of the pipe. The continuous helical seam is tightly locked and folded automatically. Corrugated pipe is fabricated in sizes from 6- to 96-in. in diameter in the regular corrugated or helical-type corrugat ed product. Pipe lengths run from 20 to 30 ft. The weight per foot of pipe depends on the pipe diameter and gage of metal used, and whether or not the pipe is coated, partially coated and paved, or fully coated. The examples in Table 23 indicate approximate weights. Lining and coating. Corrugated pipe may be obtained with different types of coatings and linings. All standard corrugated pipe is galvanized with zinc coating (2 oz per sq ft). Bituminous coatings may be applied over the galvanized surface to provide additional protection. Pipe may be par tially coated, with the invert paved. Some pipe is lined with asphalt to produce a smooth interior surface throughout the pipe (see Fig. 21). The asphalt is applied centrifugally. Another type of coating is used to produce asbestosbonded pipe, which provides resistance to severe corrosion conditions. This material is produced by pressing asbestos felt into the surface of the molten zinc coating as the flat sheets come from the galvanizing rolls. The sheets are then passed through equipment that saturates the exposed fibers. After the excess saturant is squeezed out, the sheets are cooled, corrugated, and formed into pipe, then coated with hot-dip bituminous coating. Joints are made in the field by riveting or spot welding, then coated for protection. Shipping is by truck or flatcar. Manufacturers The following companies manufacture steel pipe, but not all those listed produce pipe of all the types that have been covered in this section. American Cast Iron Pipe Co., Birmingham, Ala. American Pipe & Construction Co., Monterey Park, Calif. Armco Steel Corp., Metal Products Div., Middletown, Ohio Bethlehem Steel Corp., Bethlehem, Pa. Lone Star Steel Co., Dallas, Tex. Republic Steel Corp., Cleveland, Ohio Southern Pipe & Casing Co., Azusa, Calif. Thompson Pipe & Steel Co., Denver, Colo. Traverse City Iron Works, Traverse City, Mich Trinity Valley Iron & Steel Co., Fort Worth, Tex U. S. Steel Corp., Pittsburgh, Pa. M 40 I WATER AND WASTES ENGINEERING Section 12--Wrought Iron Pipe In the field of wastewater disposal, wrought iron pipe is used in pumping stations, for force mains, stream crossings (both underwater and aerial), outfall lines, sewer system downshafts, and in treatment plant piping systems. Inplant piping systems that may consist of wrought iron pipe in clude influent and effluent lines to various processes, lines for handling all types of sludge, for transporting chemi cal solutions, gas, air. oil, water, sewage, and chlorine, for sludge digester heating systems, and for plant heating sys tems. For some applications, galvanized wrought iron pipe may be used. Wrought iron pipe is also used for guard railings. Other applications of wrought iron in wastewater disposal systems include manhole steps, weir plates, bar screens, tide gates, etc. Design and manufacture Wrought iron pipes and fittings used in wastewater dis posal systems are the same as those manufactured for use in water supply systems. The composition of wrought iron pipe, its physical, chemical, and mechanical properties, methods of manufac ture, coating and lining, handling, and shipping, as well as the available sizes, are covered in some detail in Manual of Practice No. 2 (pp. M33 to M35).24 Characteristics There are several characteristics that make wrought iron pipe useful in wastewater disposal and inplant piping sys tems. For example, it is resistant to internal and external cor rosion, has mechanical strength to resist shock and fatigue, has a smooth internal surface to provide good hydraulic flow characteristics, has abrasion resistant properties, is weldable, and can be coated and lined to meet conditions encountered in operation. Manufacturers The following companies produce wrought iron pipe for use in wastewater disposal systems. A. M. Byers Co., Ambridge, Pa. Grinnell Co. Inc., Providence, R.I. Section 13--Pipe Lining in the Field The lining and coating of various kinds of pipe during manufacture has been discussed in the previous sections of Part 2. This section is devoted to the lining of new pipe in the field, either before or after placement. Lining-in-place of existing sewers is a maintenance matter and is discussed in Part 4. Cement-mortar Cement-mortar lining may be applied to pipe sections before installation or to new lines after installation. The equipment and method of application used are the same as those for water main lining-in-place (see Manual of Prac tice No. 2, p. M 48).24 This method of lining is applicable to any type of pipe where lining appears to be warranted to meet conditions in the sewer. In 4- to 144-in. diam. pipe, the lining may be done by special machines that utilize centrifugal application of the cement mortar. The mandrel process for applying cementmortar linings may be used for pipes from 4 to 16 in. in di ameter. CTD014858 Epoxy lining* Acid-resistant epoxy mortar lining may be applied at the manufacturer's yard to new concrete pipe or in the field to pipe from 24 to 144 in. in diameter. The lining material is composed of liquid epoxy resin, amine hardener, and inert material. The epoxy resin is a condensation product of biphenol and epichlorhydrin (in various ratios). When epoxy resins are reacted with amines, amides, and similar chemicals, cold-cure epoxy compounds are produced. A number of formulations for sewer lining are available to resist various types of wastes, including oils, greases, acids, alkalies, etc. The formulations consist of a liquid epoxy resin modified with an amine hardener to provide flexibility, high impact strength, fast curing, and good chemical resistance. The'liquid resin-hardener is combined with clean silica sand, coke, or other inert materials to pro vide hardness and abrasion resistance and to improve the thermal expansion characteristics of the lining. The method of applying acid-resistant epoxy mortar lin ings in the field consists of lining each section of the pipe before installation, although the whole sewer line may be lined in place after installation. The epoxy mortar lining is applied centrifugally by a special machine (see Fig. 22). This type of lining may also be applied to pipe by the manu facturer. Before linings are applied in place, joint areas in concrete pipe are filled with cement mortar and troweled smooth. When the pipe is lined at the factory or on site before instal lation, the bell and spigot areas are painted with a roller or brush, using a coating of 100 percent solids epoxy. Addi tional protection may be provided by pointing up the joints after placement. Other lining materials A number of commercial lining materials may be brushed or sprayed on in the field. Included in these mate rials are asphaltic and coat tar substances, chlorinated rub- Fig. 22. Epoxy-mortar lining of concrete pipe in the field be fore installation. ber paints, vinyl plastic formulations, and epoxy resins. The selection and application of such materials should be made only after consultation with the manufacturers of such products. Manufacturers Many companies provide sewer lining services or manu facture materials for lining new sewer pipe before or imme diately after installation. The following list is not necessarily all-inclusive. Furthermore, none of the companies listed here provides all the types of linings and lining materials discussed in this section. Some of these companies provide only one or two types of linings, others provide application service, still others supply only the coating material. Ace Pipe Cleaning Co., Inc., Kansas City, Mo. Amercoat, Inc., Brea, Calif. American Pipe and Construction Co., Monterey Park, Calif. Centriline Div., Raymond International, Inc., New York, N. Y. Halliburton Co., Duncan, Okla. Inertol, Inc., Newark, N. J. Koppers Co. Inc., Tar and Chem. Div., Pittsburgh, Pa. Mainlining Service, Inc., North Tonawanda, N. Y. National Power Rodding Corp., Chicago, 111. National Water Main Cleaning Co., Newark, N. J. Pipe Linings, Inc., Wilmington, Calif. Protectowrap Co., Denver, Colo. Reilly Tar and Chem. Co., Indianapolis, Ind. Robinson Pipe Cleaning Co., Canonsburg, Pa. Section 14--inplant Piping Systems In the selection of pipe materials for inplant piping sys tems, the design engineer must consider the particular use of a pipeline and the conditions to be encountered. For example, consideration must be given to the material's abil ity to withstand attack by the fluid carried and to withstand the expected operating pressures and temperatures. Obvi ously, a pipeline that will carry an acid solution must be acid-resistant; lines intended to carry a liquid having a high grit content should be abrasion-resistant; heating system lines should be unaffected by temperature; lines for carry ing digestion tank gas should be resistant to low pH, hy drogen sulfide, etc. Pipelines that carry raw sludge may become coated in ternally with grease layers, which must be removed at in tervals. Such grease accumulations may be removed by pumping hot water through the lines or by using mechani cal cleaning equipment. If hot water cleaning is used, the pipe and its joints must be capable of withstanding the ex pansion caused by the temperature increase. If mechanical cleaning is used, the lines must be able to withstand the scraping action of the equipment. Lines that become clogged by the deposition of calcium carbonate, as in the vacuum filter discharge from limecondition sludge dewatering operations, may have to be cleaned by acid. Within such restrictions as ma^be imposed by the con ditions mentioned or other operating conditions, the design engineer has a wide range of materials available for use in inplant piping systems, including asbestos-cement, cast iron, concrete, reinforced resins, plastics, steel and wrought iron. Clay pipe may be used for inplant sewer systems; rubber (both hard and flexible) or glass may be used for chemi cal feed lines, copper or brass may be used for lines serv ing hydraulic or pneumatic valve or instrument systems, etc. This manual will not attempt to cover brass, copper, glass, or rubber piping materials. SEPTEMBER 1967 | M 41 CTD014859 PART 3/INSTALLATION PRACTICES Section 1--Trenching Practices The practices involved in excavating trenches for sewer pipe are generally applicable to all types of pipe materials. For information on tunneling, see WPCF Manual of Prac tice No. 9.20 Excavation Trenching for sewer lines, like that for water lines,24 may be done by hand or by trenching machine, backhoe, clamshell, dragline, or front-end loader. The choice of ma chine may depend on the location of the sewer; that is, in open country, one type of equipment might be used, but in built-up or paved areas, another type of equipment might be more practical. Trench depth. In general, the trench should be dug no deeper than necessary for meeting the elevation of the gradeline as established by hydraulic design. Generally, too. it is not necessary to lay a sewer below the frostline unless there is a possibility of frost heave, hut, as pointed out pre viously, the trench-bottom grade should avoid "bucking" the surface grade, wherever possible, to avoid excess exca vation. Except in rock ledge or water bearing soil, mechani cal excavation is usually stopped about 4 in. above the in vert elevation, and the remaining excavation is done by hand. (See discussion under bedding, below.) Trench width. For a discussion of trench width, see Part 2. Section 2. and also Manual of Practice No. 2.24 The minimum width of trench used must allow room for the pipe installers to work. Widths given in Manual of Prac tice No. 2 (p. M38)24 for asbestos-cement, cast iron, and concrete pipe are applicable to sewer pipelines. When sew ers are laid on a curve, wider trenches are required for most types of pipe (except for those that are flexible). For clay pipe sewers, the maximum permissible trench v idth is usually set forth in the project specifications, but it is generally equal to the outside diameter of the pipe socket (or bell) plus 12 in. Recommended trench widths are shown in Table 24. Excavated material. The soil excavated from the trench should be piled on one side of the trench in such a way as to prevent it from rolling back into the open trench. The pile should be placed far enough from the side of trench to allow walking room between the pile and trench. Pipe should be strung on the side of the trench opposite the pile. . Under most conditions, a trench should be opened for no more than two pipe lengths ahead of the installation. The procedure to be followed if rock or bad soil is en countered is generally the same for sewer pipe as for water TABLE 24--RECOMMENDED TRENCH WIDTHS FOR CLAY PIPE* (Measured at top ol pipe) Pipe size (in.) 6 8 10 12 15 18 21 24 27 30 33 36 Trench width (t> 1-3/4 2 2-1/4 2-1/2 2-3/4 3 3-1/2 3-3/4 4 4-1/2 4-3/4 5 M 42 | WATER AND WASTES ENGINEERING lines.24 Where ledge rock is encountered, excavation is usually to a depth of 12 in. below grade. For other rock for mation excavation procedures, see Manual of Practice No. 2.24 In bad soil, excavation below grade and placement of selected bedding may be done for two reasons: To protect pipe that is not acid-resistant, and to compensate for soil (particularly fill) that will not provide good support. Sheeting and bracing The need to use sheeting and bracing in sewer construc tion projects depends on the depth of trench, condition of the soil, requirements of state accident commissions, and local ordinances, where they exist. Safety of both workmen and the public is essential, and trench sidewalls should be protected against cave-in whenever the possibility exists. Simple or skeleton bracing may be obtained with 12-in. planks (2 or 3 in. thick) braced by pipe trench jacks. For wider trenches or for poor soil, a system of wales and tim ber cross struts, or a movable shield, may be required (see Fig. 17 in Manual of Practice No. 224 or see WPCF Man ual of Practice No. 9.)26 Dewatering Sewer pipe should be laid in dry trenches, not only to en sure good bedding, but also to allow jointing procedures to be done properly. There are two basic methods for dewater ing trenches: simple pumping from the trench and well point pumping. In the simple method, the suction line of a contractor's pump is dropped into the trench, and the pump is operated as necessary to remove accumulated water. One variation of this method involves placing a 4- to 6-in. bed of suitable drainage material below grade in the trench bottom to facil itate flow of water to the pump suction line. Another varia tion is the placement of a perforated drain tile or pipe in the bed of drainage material, gravel, or rock used as selected bedding for the sewer pipe. The other basic method of dewatering employs wellpoints driven on either side of the trench to a depth below the level of the trench bottom. The system is operated con tinuously to keep the ground water level below the trench bottom. Section 2--Pipe Installation Many practices involved in installation of sewer piping are the same as those for water mains: some are applicable to different types of pipe material. The following discussion will cover both general practices and practices applicable to particular pipe materials. Pipe handling In the unloading of sewer pipe from trucks or railroad cars and the subsequent handling and stringing along the right of way of the sewer, care and attention should be exer cised, as in handling water supply pipe. This subject is dis cussed in Manual of Practice No 2 (p M37).24 The admonitions given there are also applicable to types of pipe not discussed in that manual, e.g.. bituminized-fiber, clay, reinforced resin pipe. etc. Bedding Part 2, Section 2 of this manual contains a discussion of the relation of bedding conditions to supporting strength of the pipe, and the relation of supporting strength to the se lection of pipe material and pipe class. Besides supporting CTD014860 < strength, three factors must be considered in selecting the type of bedding to be specified on a sewer construction project. These factors are: cost of construction, stabilization necessary to overcome poor soil conditions, and possible soil subsidence during the life of the sewer. Good soiL In good day soil that is free of excessive water, sewer pipe can be laid simply; the only requirement is that the trench width and bottom shape conform to the pipe dimensions. Overexcavation and backfilling may be less costly than trimming of trench bottoms to fit the pipe shape. Such backfilling is done with pea or roofer's gravel to provide a bedding that shapes iteslf to the pipe and pro vides the necessary supporting strength. Poor soil. Soft or poor soils may require overexcavation to some appreciable depth with backfill of coarse gravel or rock covered by pea gravel. The need for such stabilization usually can be determined only as excavation proceeds. Bad soil. Where soil is very poor or is subject to future subsidence, it may be necessary to install timber platforms, reinforced concrete cradles, or piling driven to grade be fore excavation. Joint holes. As in the laying of water pipe, the trench bot tom must provide for the particular type of joint used. Joint-hole preparation for asbestos-cement, cast iron, con crete, plastic, steel and wrought-iron pipe is covered in Manual of Practice No. 2 (p. M39).24 Pipe placement There are a number of general directions that apply to the laying of all types of sewer pipe: Individual lengths of pipe should be inspected for damage before being lowered into the trench, and dirt or foreign matter should be removed, particularly at the ends. Pipe lengths should be handled with care in being low ered into the trench, whether the lowering is done by hand, by snub ropes, or by machine. Pipe should never be pushed off the side of the trench, no matter how shallow. Bell and spigot type pipe should always be laid upgrade, with the bell facing upgrade. Pipe that uses other types of joints may be laid in either direction, but it is preferable to lay it upgrade because the trench will act as a drain, reduc ing the soil moisture content. When pipelaying is not in progress, the open pipe end should be closed with a tight fitting stopper to keep out fo reign matter. Where the sewer direction changes on a predetermined curve, the pipe lengths should be deflected no more than the maximum recommended by the manufacturer. For deflec tion data on asbestos-cement, cast iron, mechanical joint, and concrete pipe see Tables 35, 36, 37 in Manual of Prac tice No. 2.24 Allowable deflections in clay pipe sewer lines are as follows: Pipe size (in.) 4-12 15-24 27-36 Deflection (in./lin ft) 1/2 3/8 1/4 Pipe grade and line The grade of the trench bedding, that is, the sewer invert grade, as well as the line, should conform to the design and specifications; it is the inspector's responsibility to check this conformance. Probably the most common method of ensuring that the desired grade is obtained is the use of grade bars (batter boards) and taut strings, checked by standard surveying instruments. Another method for ensuring that the desired pipe grade is obtained employs a laser beam produced by an automatic grade light.38 Utilizing a single batter board and pole ar rangement at one point (e.g., a manhole) and a mirror (pipe target) at the next joint to be made, it is possible to maintain both correct grade and a straight line as the pipe lengths are laid. The method has several advantages: pipelaying may pro ceed directly behind a digging machine; the setting of batter boards is eliminated; excavation to grade is more accurate because of constant reference; less manpower is required; and pipelaying time may be cut as much as 20 percent. Jointing procedures According to WPCF Manual of Practice No. 9,2C "the characteristics of a good joint in sewer pipe include water tightness, resistance to root penetration, resistance to corro sion, a reasonable degree of flexibility, and durability." The desirability of these characteristics is evident in light of pre vious discussion of infiltration, root penetration, etc. The characteristics desired may be obtained with any type of currently available joint if care is used in making the joint. Joint flexibility is not possible with flange joints, screwed couplings, and welded joints. Flanged joints are used only for inplant piping, where flexibility is unneces sary. Screwed couplings and welded joints (either electric or solvent-weld) usually are made on pipe that is made of ma terials with some degree of inherent flexibility. The joints available for each pipe material are discussed in Part 2. The jointing procedure used in sewer construction de pends on pipe material, type of joint, and the type of equip ment used for mating the joint. The following discussion is organized on the basis of pipe material. Several of the var ious pipe materials utilize a rubber-gasket joint and differ ent methods of securing the joint. One method applicable to rubber gasket joints for all types of pipe employs a unique device known as a "pipe popper" (Fig. 23). The steel and aluminum device, for use on sewer pipe 18 to 42 in., consists of two main sections, a spring-loaded anchoring assembly, and a removable jacking unit. The sketch in Fig. 23 indicates the construction ar rangement and the operation of the device. Joint mating is performed quickly by one man. Methods of cutting pipe in the field to make joints or to insert fittings will be covered in Manual of Practice No. 4. ASBESTOS-CEMENT PIPE The same general type of coupling and rubber-ring gasket joint is used for both pressure and nonpressure asbestos-ce ment pipe. Jointing is essentially the same as for water mains (see Manual of Practice No. 2, p. M40.)24 The pipe is delivered with a rubber ring and the coupling in place on one end of the pipe, generally termed the "belled end." As in the laying of all bell and spigot pipe, the bell end is laid in the direction of construction. The joint is made in the following manner: the inside of the coupling is cleaned, and the rubber gasket is inserted in the depression inside the open end of the coupling; the "un belted" end of the pipe is properly lubricated and inserted Fig. 23. Device for mating gasketed pipe joints. SEPTEMBER 1967 ] M 43 CTD014861 into the coupling; and the pipe is "pushed home" until the joint is seated properly. "Pushing the pipe home" may be done by using a crow bar to exert pressure against a block of wood across the free end of the pipe.2-* A mechanical puller device may be used to seat large sizes of pipe, but the use of such equipment should be in accordance with manufacturer's directions. BITUMINIZED-FIBER PIPE In sizes up to 8-in. diam., bituminized-fiber pipe is fur nished with 2-degree tapered ends and couplings to match; sizes from 8 to 18 in. are furnished with push-fit collars. Pipe ends may be cut or tapered in the field. Large size pipe may be joined by butyl-rubber collars tightened by steel bands. For the tapered-end or push-fit collars, jointing is accom plished by placing the 12-in. coupling on the forward end of the pipe, then placing a wooden block over the coupling and tapping the block with a hammer or light sledge to drive the coupling tight. The next length is then inserted into the cleaned, free end of the coupling and driven home by pres sure exerted against a block at the next coupling. More se cure joints and tighter seals may be obtained, if required, by brushing a solvent-adhesive compound into the free end of the pipe before it is inserted into the coupling. CAST IRON PIPE Joints on cast iron pipe sewers are made in the same way as those on water supply lines, whether the type of joint is bell and spigot, mechanical, push-on, or flexible ball and socket. Details of jointing procedures for cast iron pipe joints are given in Manual of Practice No. 2 (pp. M40) ,24 CLAY PIPE Clay pipe joints are of the bell and spigot type, therefore, jointing procedures are determined by the materials used to make the joint tight. Several kinds of material, in different forms, have been or are used in making up clay pipe joints. Mortar-jute. Joints made with this material are no longer recommended because they are rigid, are not resistant to acid, and are hard to make up properly, particularly be neath the pipe. This type of material was die first used in making "tight" joints. The procedure consisted of calking oakum or jute into the rear of the annular space between the bell and spigot, then packing with cement mortar. Pressure mortar. This type of jointing material is applied by packing mortar against a removable flange form. Al though joints made with this material were an improvement over mortar jute joints, the disadvantages of cement-mortar were not eliminated. Hot-poured bitumen. A joint made with this material is known generally as a hot-poured joint. The jointing proce dure is very much like that used for lead joints on bell and spigot cast iron pipe.24 The spigot end of the clay pipe is centered in the bell by a ring of calked jute, then melted bituminous material is poured into the joint. The joint is provided with an asbestos-rope snake and gate to permit pouring and to hold the melted material until it cools and sets. The cooled material is then calked into the bell to pro duce a tight seal. Disadvantages of bitumen joints include the tendency to become brittle when cold and to flow in warm weather; the difficulty of pouring in cold weather; and the tendency to form steam with extraneous moisture on the pipe surface, causing impairment of surface adhesion or appearance of fissures in the sealing block. Cold bitumens. There are three methods of making joints with cold bituminous materials. These procedures do not have the disadvantages of hot-pouring procedures, but the weakness of the material--the tendency to crack in cold weather and flow in warm weather--is the same. Buttered-bitumen. Another material used for making clay M 44 I WATER ANO WASTES ENGINEERING pipe joints is a plasticized bitumen, in which a softening agent has produced a "butter" that can be troweled into the annular space around the spigot end in the bell. This mater ial will air-set as the "solvent" evaporates. Ribbon-gasket. An extruded ribbon gasket, which may be fortified with fibers or dust, may be used for making joints. The ribbon is wound around the pipe and calked into the bell, without using heat. Slip-seal. In making slip-seal joints, which are also called die cast or premolded joints, complementary precast rings are placed around the spigot and inside the bell. Both rings have a tapered design. When pushed together, they become wedged, causing the joint to become sealed. These rings are generally cast on the pipe at the factory. Sulfur-silica. This type of material is a mixture of sulfur and sand; it is poured hot and sets as it cools. It tends to be brittle and may be attacked by sulfur-eating bacteria. Compression joint. Materials that may be used in making this type of joint are natural or synthetic rubber, e.g., neo prene, or plastics and resins, such as polyvinyl chloride, po lyesters, polyurethanes, epoxies, etc. These materials all have the same advantages; they form flexible joints that allow for maximum deflection; they are resistant to the acids, alkalies, and gases generally found in a sewer; they do not require the use of a spacing material such as jute; they are not subject to shape changes during storage, regardless of weather or temperature; they are re sistant to shear loading; when designed for the proper resid ual compression, they resist leakage, root penetration, de flection and shear; and they do not require the use of heat in the jointing process. Only one disadvantage is noted; some wastes may attack or tend to dissolve these jointing materials. These effects can usually be avoided by proper selection of materials. These jointing materials are manufactured in accordance with ASTM Des. C425-60T. which also specifies laboratory test requirements and field, performance and acceptance tests. There are three types of joints covered by this ASTM specification. Type I. The same resilient joint material is used in the bell and on the spigot. Either one of the rings may differ in hardness from the other, but controlled complementary de sign ensures a positive mating pattern of closure. Type II. Jointing material on the spigot end may differ in composition from that in the bell, and the hardness and resi liency of one may differ from that of the other, but the con trolled complementary design will ensure proper mating and closure. Type III. The jointing material is a single, true-round, resilient gasket or compression ring. It has a controlled and calculated final shape within the annular space after the joint is made. The gasket or ring may or may not be at tached to the spigot or inserted in the bell at the time the pipe is manufactured. Make-up procedure. The procedures for making up these compression ring joints are practically the same for all types. Lubricating materials are applied to the pipe end or gasket to offset frictional resistance during the insertion of the spigot into the bell. Pressure is applied to the end of each pipe to force it home and provide the desired joint. CONCRETE PIPE The jointing procedure for concrete pressure pipe in a force main or pressurized sewer is the same as that for con crete water mains, as described in Manual of Practice No. 2 (p. M41).'-'4 For gravity sewer lines, the choice of the jointing procedure will depend on the type of joint and jointing material used. Regardless of joint type or material, "construction" should be done in a manner that will ensure watertightness and resistance to root penetration. In preparing project specifications, the design engineer will call for one of four types of joints (bell and spigot, ton- CTD014862 < gue and groove, modified tongue and groove, or a collar of concrete or other material) and for one of three types of jointing procedures (using cement mortar, commercial jointing compound, or single rubber ring gasket). Jointing compounds. A number of commercial products are available for use with bell and spigot, tongue and groove, or modified tongue and groove joints. The com pounds include combinations of coal tar and mineral fibers, bitumastic, creosote, sulfur-silica, asphalt, resins and gums, and various other patented materials. The jointing com pound should be selected on the basis of experience. Cement-mortar bell and spigot joint. In making up this type of joint, the interiors of both the bell and the spigot are cleaned and wetted and a stiff cement-mortar (one part Portland cement and two parts clean fine sand) is applied. The steps involved in making the joint include placing the mortar, fitting the spigot into the bell, forming a mortar bead around the joint inside the pipe, and smoothing the mortar bead.29 Cement-mortar tongue and groove. The first step in mak ing this type of joint is the cleaning and wetting of both the tongue and the groove. Then cement mortar is carefully placed under the pipe and in the bottom of the joint. The free pipe is inserted into the previously laid section, and the annular space is filled with mortar. During the fitting opera tion, mortar is squeezed out onto the inner and outer sur faces of the pipe. The inner joint surface is smoothed by a long-handled brush; the outer bead pointed by trowel. Diaper joint on bell and spigot. The procedure for mak ing this type of joint begins with calking jute into the bell. Next the joint is wrapped with a diaper cloth of heavy can vas. the edges of which contain flexible wire, and the wires are tightened. A wet sand-cement grout is then poured into the joint or pumped in through a funnel, using a plunger pump. The diaper is left in place after filling. A tight joint is obtained, even if the joint is made in a wet trench.29 Diaper joint on tongue and groove. In making this type of joint, a cheese cloth dipped in portland cement-mortar is wrapped around a conventional tongue and groove joint. An 8-in. wide diaper is used to hold a' 1/2-in. layer of cement-mortar in place during curing. The band is cured with a covering of moist earth, sand, canvas, or burlap. If backfilling is not done immediately, curing with water for 48 hr is required.29 Cement-mortar oakum joint for bell and spigot. The pro cedure for making this type of joint is essentially the same as those described for bell and spigot water pipe24 and for cement-mortar joints on clay pipes. There is one difference: the oakum is dipped in cement-mortar (one part cement to two parts sand), and the calking is done about four or five lengths behind the placement operation.29 Cement-mortar oakum joint for large diameter tongue and groove. In this jointing procedure, the tongue and groove pipe is laid as previously described except that oakum is used in addition to the cement-mortar. In pipes larger than 76-in. diam.. the calking is done from inside the pipe. The oakum is dipped in cement-mortar before being placed. For smaller pipe sizes, calking is done from the outside.29 Concrete collar. A prefabricated reinforced concrete col lar is attached to one end of each pipe length at the manu facturing plant. The collar is calked in layers onto the pipe end with neat cement (two parts cement to one part sand) until the collar is full. Approximately half the collar length extends beyond the end of the pipe. Reinforcing in the col lar should correspond to reinforcing in the pipe, and the collars should be made by the process used for the pipe. Collars are at least 7 in. long and range in thickness from l-.V- 8 in. for 8 in. pipe diam.. to 5-in. (minimum) for 72- in. pipe When the pipe joint is made up. the uncollared end of a pipe section is inserted into the collar of a previously laid pipe section, and the joint is sealed by calking cement-mor tar (two parts cement to one part sand). After the joint is made up, it is covered with a moist cloth and cured for three days.29 Cement-mortar, tongue and groove, with external bands. In some installations, external bands of concrete mortar are used on tongue and groove joints. The jointing procedure consists of hand placing a stiff mortar around the joint to form an encircling band. The operation is usually carried out four or five lengths behind the laying operation. Back filling of the trench to the springline of the pipe is done im mediately to prevent the band from falling off. The mortar used in making the band is stiffer than that used between the joint surfaces. Protection and curing are essential to the strength of the final joint. Such external bands are usually not required on heavy-wall pipe with tongue and groove joints but may be used on lines less than 24 in. in diameter. The details of making this type of joint appear in the Con crete Pipe Handbook.29 Single-rubber-ring gasket. Because of its economy, ease of construction, and satisfactory performance record, the single-rubber-ring gasket joint has largely superseded all other types of joints for use on concrete sewer lines.29 In the manufacture of the pipe, the ends are produced with attention to close tolerances, and a space is left for the rubber ring. The procedure for making up the joint is gener ally the same as that described previously for asbestos-ce ment, cast iron, and clay pipe joints utilizing flexible ring gaskets. Jointing compounds. The procedure for making up bell and spigot joints with commercial compounds such as bitu mastic, asphalt, resins, etc., is practically the same as that described previously for clay pipe. Fiberglass reinforced collar. This type of joint closure is used on concrete pipe with recessed spigots on both ends, each spigot having a recessed space to hold a rubber ring gasket. The band or collar is made of epoxy resin impreg nated with fiberglass rovings and fiberglass fabric in various combinations. The glass strands are wound circumferential ly on a form to obtain the desired tensile strength and elasti city. This band is generally used in pressure pipe systems and is corrosion-resistant, resilient, and flexible; it permits up to 1-in. angular deflection on curves, and is made in sizes from 12 to 72 in. inside diameter. The jointing procedure consists of placing the rubber ring gaskets on the ends of the pipe and seating the band. Noncircular pipe jointing. When elliptical or other noncircular pipe is installed, it should be placed in accordance with the manufacturer's labels of "bottom" or "top," and should not be more than 5 degrees from the vertical or hori zontal axis. Care must be exercised in placing the pipe joint to ensure that each section is in the same vertical or hori zontal axis as the previous length. Tongue and groove joints are used, and the procedure for making up the joint is the same as described previously. PLASTIC PIPE The procedure used for jointing plastic pipe depends on the type of pipe, pipe size, and type of joint. Generally, the joints are made outside the trench, particularly for small sizes, and the pipe is then lowered into the trench. ABS pipe. In small sizes, this type of pipe may be joined by victaulic or Dresser-type joints or by solvent welding In the solvent-weld procedure, the tapered pipe ends (male and female) are brushed by a solvent that softens the plas tic. then pushed together and the two pipe sections turned slightly against each other to form a tight grip. Chemical in teraction between the two ends takes place as the solvent evaporates, and the pipe is permanently joined. PE pipe. The jointing procedures for PE pipe were given in Manual of Practice No. 2 (p. M26).24 PVC pipe. The solvent-weld method of jointing is appli- CTD014863 SEPTEMBER 1967 | M 45 cable to PVC pipe joints employing couplings and to bell and spigot PVC pipe. Some PVC pipe produced has a bell end in which a rub ber O-ring gasket is fitted. Jointing is accomplished by pushing the spigot end into the bell, thereby compressing the O-ring and forming a watertight seal. Styrene-rubber plastic pipe. This type of pipe is joined using a coupling and the solvent-weld procedure. The inside of the coupling and the outside of the pipe end are brushed with a "cement" solvent; the pipe end is inserted into the coupling and given a quarter turn to distribute the cement. Within 20 to 30 min. the joint is dry. Joints may be made either inside or outside the trench. Truss-type plastic pipe. This type of pipe is composed of an ABS plastic and utilizes a coupling and chemical welding process for making the joint. The pipe end and inside of the coupling are first brushed with a primer, then with a "cement." The pipe end is then "shoved home" into the cou pling and given a quarter turn. Sufficient cement should be used to produce a continuous bead between the end of the coupling and the pipe surface. When making the joint, the pipe installer must make certain that the pipe is "all the way home" upon insertion. If it is not, he must remove the pipe immediately, clean the ends and the coupling, and repeat the cementing operation. Plastic lined pipe. This type of pipe is generally joined by flanged fitting or couplings screwed to threaded pipe ends. Plastic liners. Plastic liners for concrete sewers are des cribed in Part 2, Section 8. This lining material is joined by heat-welding the liner in one section of pipe to that in the next, forming a continuous lining. REINFORCED RESIN PIPE Glass-reinforced resin pipe is joined by a solvent-weld procedure using couplings. Joints may also be made by wrapping the butted or jointed pipe ends with fiberglass cloth impregnated with a resin and softened by a solvent. As the cloth is wrapped around the pipe, liquefied resin is brushed on. Any joint thickness may be obtained. Reinforced plastic-mortar pipe has a bell and spigot type joint that utilizes a rubber ring gasket. The jointing proce dure is similar to that used for any other bell and spigot Oring gasket joint. STEEL Procedures used for jointing steel pressure sewers depend on the type of coating and lining. Generally, the procedures used are the same as those for water supply piping.24 WROUGHT IRON PIPE Welding procedures for jointing wrought iron pipe sewers are the same as those for water supply lines.24 Inspection and Testing Specifications for inspecting and testing sewer lines after installation are not generally as detailed or complete as those for water supply lines. There are, however, some ASTM specifications for field performance and acceptance testing of sewers. Also, some organizations, governmental bureaus, and consulting engineers have developed their own specifications for inspection and testing of newly installed sewer lines. The following discussion presents several speci fications that may be considered typical. INSPECTION Three areas require inspection during or after construc tion. Any deficiencies found must be corrected so that the sewer construction meets specifications. Grade and line. During the course of construction of a sewer line, both the grade and the line of direction should be checked at regular intervals--certainly from manhole to manhole, and sometimes from pipe length to pipe length M 46 I WATER AND WASTES ENGINEERING 5 --depending on soil conditions, bedding, type of pipe, and type of joint. Methods for checking grade and line have been discussed previously. Bedding. Where particular types of bedding or selected fill are specified, or where areas of bad soil or rock excava tions may be encountered, the bedding or fill should be checked regularly to make certain that it meets the specifi cations. Sewer interiors. Sewers larger than 30 in. in diameter can be entered and examined carefully for uneven grades, cracked or broken pipe, excessive water leakage at joints, debris, or irregular surfaces at joints. Small sewers may be inspected between manholes by strohg light directed down the sewer barrel or by TV. Manhole interiors should be in spected at the same time time as the sewers. Unacceptable conditions in sewer interiors should be remedied. All sewers should be flushed after construction and before testing. TESTING Testing of sewers consists of determination of infiltration and exfiltration, or of leakage from force mains. Force mains. Before backfilling, pressure sewers should be tested at a hydrostatic pressure of 60 psi for at least 30 min, and all fittings, valves, and joints should be inspected for leaks. Repairs should be made where necessary. After backfilling, hydrostatic tests should be made for at least 24 hr at 40 psi. Leakage should be less than 50 gpd per in. diam. per mile. Infiltration. Infiltration tests are usually made by sealing off a length of sewer, then actually measuring the infiltra tion for a period of several hours. Measurements may be made by a weir, or by pumping the discharge through a meter, or by measuring it in some other manner.4 Accept able limits for infiltration were stated in Part 1. Exfiltration. Exfiltration or head tests are used to mea sure the tightness of the sewer. Generally, exfiltration tests are made in a dry trench. These tests are usually made by closing off a section of the sewer and the manhole at the upper end of the section. The line is then filled with water under a head of from 1 to 4 ft above the upper manhole in vert. Measurement of exfiltration (leakage) is made by re cording the drop in water level in the manhole over a period of time. If the leakage rate is great, it may be measured by metering water into the manhole at a rate just sufficient to maintain a constant water level. In the exfiltration test, it is necessary to consider possible absorption of water by the pipe and manholes and leakage from the manholes themselves. The test is valid only if all fittings, tees, and wyes are stoppered tightly and if all en trapped air was bled off as the line was being filled. Specifications for acceptable exfiltration rates should be based on engineering judgment, with due consideration of all factors involved. A typical acceptable limit is 100 gpd per in. diam. per mile of pipe. Air testing. Another way of determining the tightness of a sewer line is by the low pressure air test.39 In this test, all J CTD014864 i stubs, wyes, tees, and pipe ends are tightly capped; the line is cleaned, plugged, and placed under air pressure. Figure 24 shows one system for making such a test. At the start of the test, the air pressure is raised to 4 psig greater than the average backpressure of any ground water. After 2 min or more, during which the air temperature is stabilized, testing is started at a pressure of 3.5 psig. The time required for the pressure to drop from 3.5 to 2.5 psig is determined as the basic measurement of the test. Various engineers and organizations have set minimum time limits as acceptable for this drop of 1 psig. Some time limit ranges for different sizes of pipe are as follows: Pipe size (In.) 4 6 8 10 12 15 18 21 24 Time allowed for 1 psig drop (min) 2 3 4 5 5.5 7.5 8.5 10.0 11.5 Other engineers and organizations have different ways of expressing the acceptable leakage rates. Some early meth ods specified the time allowed for 1 psig drop in seconds per linear foot, but this method is now considered as the less satisfactory approach. Other engineers specify that a sewer line will be acceptable when, at a test pressure of 3 psig (above ground water pressure), the total rate of air loss from the section under test is no greater than 2.0 cfm, or 0.0030 cfm per sq ft of internal pipe surface. This type of test has also been used in sewer maintenance surveys to determine sewer repair needs. Backfilling The backfilling operation is just as important in sewer construction as it is in the laying of water mains. The meth od of backfilling will depend on trench width, character of excavated soil, excavation method used, degree of compac tion required, and type of pipe material. BACKFILL MATERIAL Regardless of type of pipe material or method used for backfilling, the backfill material should be good soil; it should contain no large rocks, no bad soil, and no large clay lumps. The material placed at the sides of and immediately above the pipe should be of the best possible quality; it should be readily compactable soil or granular fill. Selected granular fill material may be crushed stone or pea gravel. COMPACTION The degree of compaction required depends on the loca tion of the sewer. In open country, compaction is usually unnecessary; under city streets, a high degree of compaction may be necessary, particularly if the street surface is to be restored immediately; and under flexible macadam paving, compaction required is more than in open country, but less than in the city. The method of compaction depends on the type of soil used for backfill. Cohesive clays, except in small particle sizes, cannot be compacted by flooding or jetting. Mechani cal tamping may be possible if the particle size is not too large. In wide trenches, clays are usually removed as large lumps, and these do not compact well unless placed in thin layers and compacted by power equipment. Blending of clay lumps with sand makes compaction possible by dozers or rollers. Granular, cohesionless material may be consolidated by flooding and poling, a procedure that is described in some detail in WPCF Manual of Practice No. 9.26 Granular ma terials may be readily compacted by using immersion-type vibrators as water is added to the trench. Water jetting may be used with or without vibrators. Project specifications should cover the type of material to be placed around the pipe, the depth of such material, and the method by which it is to be compacted. BACKFILLING OPERATIONS Backfilling of a trench should be done in three separate steps. Initial lift Fine granular soil or selected fill should be placed with care by hand or machine to a depth of 1 ft above the top of the pipe. The pipe should not be disturbed during placement operations. After the soil is placed, it should be compacted by flooding, jetting, or mechanical equipment, as described previously. If compaction by water jetting is not feasible, the backfill should be added in 4- to 6-in. layers and compacted by machine. Layering and com paction may also be more feasible on large diameter pipe. Jetting operations should be performed with care to avoid floating the pipe. Intermediate lift This second "layer" of backfill should extend from 1 ft above the pipe to 1 ft or less below the ground surface. This "lift" may be added all at one time if the backfill material is not cohesive. Compaction by flood ing and poling or jetting should follow, to produce the de-, sired degree of compaction. Cohesive soils (clay, etc.) should be placed in 4- to 6-in. layers and compacted by ma chines. If the excavated soil can not be compacted by these methods, selected fill must be used. Final lift. The final layer should consist of relatively dry material mounded slightly above the ground level. Surface restoration. Some time after backfill operations are completed, paved surfaces should be restored,26 using acceptable street paving methods. Special problems In some locations, sewers may have to be constructed under railroads, under principal traffic arteries, across ra vines, and under or over streams. Such installations require special construction methods,26 which will not be covered in this manual. The construction of outfall structures also requires special techniques26 that are not covered here. Section 3--House Sewers and Inplant Systems House sewers House sewers, preferably larger than 4-in. in diameter, should be laid with a minimum slope of 1/4 in. per ft, in a straight line and grade.26 Provision should be made for rodding and flushing in the event of stoppages. Joints should be tight, and general workmanship should be equal to that of street sewer installation, so as to minimize infiltration and root penetration. The house sewer should enter the street sewer at an angle of about 45 degrees from the horizontal. Such a connection will help to prevent backflooding of the house sewer when the street sewer is flowing full. Connections of house sewers to large street sewers should be made above the springline of the street sewer. Connections to deep street sewers may be made through concrete-encased, vertical risers. Additional details on house sewer installation, including diagrams, may be found in WPCF Manual No. 8.26 Inplant systems The installation of pipe in pumping stations and wastewater treatment plants is usually done during construction of the facility. The type of joint used (bell and spigot, flange, coupling, etc.) will depend on the type of pipe, the possible CTD014865 SEPTEMBER 1967 | M 47 need for dismantling the line for maintenance, the loca tion, and the type of fittings or joints available for a partic ular type of pipe. Pipe runs of more than two or three lengths usually must be supported by hangers, piers, or other means. Nonrigid pipe will usually require support (e.g., a chan nel) for the entire run. Plumbing and sewer lines may be buried inside or outside building structures. Yard sprinkling systems are always buried, and provisions should be made for draining them before cold weather. Potable water lines may be exposed within structures or buried outside, as lay out dictates. The design of inplant piping systems should be accom panied by specifications for the method of installation, joints, and supports. The specifications should also include a color-code designation for each system. PART 4/MAINTENANCE Maintenance of wastewater disposal systems is confined mostly to cleaning and repair of collection systems, al though some cleaning operations may be required in inplant piping and house sewers. Section 1--Collection Systems Many operating difficulties in wastewater treatment plants and problems in sewers are caused by such conditions in the collection system as excessive infiltration, root pene tration, deposits of grit, grease, and solids, septic conditions, hydrogen sulfide formation, and sewer deterioration. Extent of problems A survey of 225 cities, made by the author, indicated that infiltration existed in 70 percent of the systems, that it was general in about half of the systems, and that it had been on the increase in about 30 percent of the communities with old systems. The amount of infiltration ranged from 0 to 800 percent of the dry weather flow. In cities under 200,000 population, it ranged from 38 to 75 percent of dry weather flow. Sewer problems existed in 97.5 percent of the 225 com munities replying. These problems were: tree roots (in 97.5 percent of the communities), hydrogen sulfide (in 32 per cent), and acid conditions (in 31 percent). Based on the survey replies, it is estimated that 45 percent of the existing sewer systems shoV some deterioration, and 36 percent of the communities have had an average of 7 to 8 sewer failures a year. More than 90 percent of the cities replying, practice sewer cleaning and root removal; about one third use cop per sulfate for root control. Inspection policy Every municipal or industrial organization responsible for supervision of a collection system should have a main tenance department and a regular sewer inspection pro gram. The frequency of inspection and the size of the main tenance department will depend on the size of the commun ity and the size and complexity of the sewer system. The subjects of policy codes, departmental organization, person nel requirements, staff responsibilities, interdepartmental relationships, types of crews, records, permits, and other re lated general information are covered in detail in WPCF Manual of Practice No. 7.40 Whatever the system size, maintenance inspection should be made on a routine basis and repair work performed as necessary. It is not satisfactory to clean and repair sewers only when serious conditions develop. Such a policy is more costly than routine inspection and maintenance. M 48 I WATER AND WASTES ENGINEERING GENERAL INSPECTION Sanitary sewers should be inspected at least once a year. For large systems, a regular inspection schedule should be followed so that the entire system may be covered during the year. In areas where explosive hazards, stoppages, or traffic damage are likely to occur, two or three inspections should be made each year. All inspections should follow a basic plan and procedure with respect to the conditions that should be observed. Usually, an inspection crew of three workman and a fore man is sufficient; larger repair crews may be required. Procedures. The inspection crew should work from one manhole to the next, preferably up the sewer line. Observa tions should be made for the following undesirable condi tions: excessive extraneous water (infiltration, manhole cover leakage, roof drainage); gasoline or oil; gases and va pors; root penetrations; deposits or stoppages; manhole de terioration; and changes in or unevenness of sewer grade. Visual observation procedures based on experience and reference to records of previous inspections will generally serve to locate difficulties. Where excessive extraneous water is caused by leaky manhole covers or illegal roof drainage, inspections may be necessary during periods of rainfall. Infiltration from ground water, however, can be observed at any time when the ground water table is high. TV and photographic inspection is an excellent technique for locating undesirable conditions between manholes, par ticularly infiltration, poor joints, root penetration, deposits, and sewer barrel deterioration. The advent of small industrial television cameras made it possible to inspect the entire length of a sewer. Photograph ing the TV screen whenever an undesirable condition ap pears makes it possible to have a record of the condition and a notation of the exact location. Large communities may purchase TV camera equipment, others may employ a service organization for this type of inspection. Some com panies have equipment for inspecting and grouting leaking sewers in tandem operations. Cleaning sewers There are four methods that may be used in cleaning san itary sewers; flushing, cleaning with mechanical equipment, cleaning with hydraulically-propelled devices, and addition of chemicals to the sewer. The choice of method depends on the cause of the sewer problem, location, size, and type of sewer, and individual supervisor's experience. For sanitary sewers, the interval between cleaning opera tions should be adjusted to the rate at which undesirable conditions, deposits, or stoppages develop. Large and long sewers may be cleaned once every three to five years, with one-third, one-fourth, or one-fifth of the sewer cleaned each year in sectional rotation. The cleaning operations may CTD014866 be required every year or every other year in smaller and shorter sewers, and in some cases, as in dead-end or flat sewers, cleaning may be necessary several times during hot weather. FLUSHING Many communities do not permit automatic flushing devices at any point on a sewer because of the possibility of contaminating the potable water supply through cross-con nections. Other communities use flushing systems that uti lize the sewage flow itself and have an arrangement to auto matically discharge a stored volume. Where the normal flow of sewage is at a scouring velocity, there is a natural continuous flushing action, and deposits do not accumulate. Root penetration, however, may still be a problem. Flushing by fire hose is generally not effective because high velocities cannot be maintained for any considerable distance down the sewer. The best alternative is the use of hydraulically propelled devices (see below). MECHANICAL CLEANING Mechanical devices for sewer cleaning include sectional wooden rods with various tool attachments; steel buckets or cutters on cables to remove obstructions; light flexible steel rods (segmented or continuous) with end tools such as screws, augers, and sandcups; and a turbine-type cleaner with cutting knives and wire brush attachments. The procedure used in cleaning sewers that are plugged or almost plugged generally involves making one pass with sewer rods before inserting a bucket or cutter on a cable. Irregular sewers, which might be damaged by heavy equip ment, should be cleaned by light flexible steel rods coupled into a continuous line (or a continuous steel rod) to which the cleaning attachments are fastened. In using a steel rod system, the tool and rod are fed into the sewer until the obstruction is reached, then the rod is twisted by a hand ratchet or portable gasoline powered unit. Grease and heavy obstructions in sewers larger than 15 in. in diameter are generally removed with a powered turbinetype cleaner. Sand may be removed by sandcups on steel rods or by steel scoops on cables. Figure 25 shows a ma chine for feeding flexible steel cable into a sewer, also shown are a number of tool attachments and the pipe for conducting the cable into the bottom of a manhole. There are various other types of tools pulled through a sewer by winch drawn cable. These tools include root saws, collaps ible scrapers, flexible buckets, blade cutters, cork screws, sand headers, spearheads, porcupines, etc. Instructions for proper use are issued by the equipment manufacturers. HYDRAULICALLY-PROPELLED TOOLS There are several types of self-propelled hydraulic flush ing devices. Three of them are the sewer scooter, sewer hoe, and sewer (beach) ball. The design and operating principles of the latter two are shown in Fig. 26, adopted from Navdocks MO-212.'11 The use of these devices depends on a partial closure of the sewer, with a resulting buildup of head behind the device. This hydraulic head pushes the dev ice forward and allows a high velocity of liquid to escape beneath it, thus jetting away deposits.40 Another type of hydraulically self-propelled device is the turbine nozzle, which is attached to the end of a fire hose, and then introduced into the sewer. The action of the back ward-pointing jets moves the nozzle forward and pulls the hose behind it; the forward jet cuts the debris, which is flushed ahead of the nozzle. Only old fire hose should be used for this purpose, and it should be painted an identify ing color. CHEMICAL TREATMENT Copper sulfate introduced into sewers will successfully control and remove tree roots. Periodic dosage is most ef- I Fig. 25. Powered flexible steel cable sewer cleaning equip ment, with various tool attachments. fective, and the chemical may be added at manholes or through residential water closets. If addition is through manholes, the amount of chemical to be used should be de termined by trial and error and experience. If addition is through household water closets, it is generally sufficient to add 2 lb annually, preferably in the spring. The chemical should be placed in the toilet bowl and flushed with enough water to remove all crystals from the bowl. Storm sewer systems Storm sewer systems should be inspected annually, gener ally on the same schedule as sanitary sewers serving the area. Storm sewers should also be inspected after each se vere storm and should be cleaned as necessary. Cleaning should be done with mechanical tools and methods, not by hydraulically propelled tools. Force mains Where force mains are used to transport wastewater or sludge, clogging or reduction of carrying capacity may re sult from deposition of grease on the interior surface of the pipe. The need for cleaning will be indicated by a gradual increase in pumping pressures. Cleaning may be done by hydraulically-propelled go-devils. Main cleaning services are available for force main cleaning. Fig. 26. Hydraulic-self-propelled sewer cleaning tools (Above) sewer hoe; (below) beach ball. CTD014867 SEPTEMBER 1967 | M 49 Appurtenances Part 1, Section 6 discusses appurtenances, many of which require cleaning. Inlets and catch basins should be inspected during or after each severe storm, or at least annually. Equipment, such as buckets, orange peels, etc., is manufactured espe cially for cleaning inlets and catch basins, and cleaning should be done when inspection indicates its necessity. House sewer cleaning is seldom a responsibility of the municipal sewer department. The property owner usually contracts with a sewer cleaning company for that service. Traps (oil, grease, sand, etc.) should be inspected and checked at regular intervals. Experience will dictate the in terval between inspections; cleaning should be scheduled as inspections indicate the need. Iunction chambers, overflows, and similar appurtenances should be inspected after each severe storm and cleaned and repaired as necessary. Manholes should be inspected at the same time as the sewer itself. Lift stations should be inspect ed, cleaned, and maintained as set forth in Manual of Prac tice No. I.42 Outfall sewers Outfall sewers may be part of the collection system or part of the treatment plant system. If they have been prop erly designed and constructed, they will require a mini mum of maintenance, but they should be checked or in spected at regular, though perhaps extended, intervals. Inspection procedures should include checks to make cer tain that the effluent has a free outlet, that there has been no settlement of the line or the outfall structure itself, that no drifting sand (in ocean outfalls) has restricted the opening, and that floating ice or a violent storm has not damaged the outfall anchorages and foundations. Section 2--Sewer Repair Part 3 of this manual pointed out the need for proper design, proper selection of pipe, and careful installation procedures to ensure long life and resistance to infiltration, root penetration, deterioration, and pipe failure for any cause. With modern pipe and pipe joint design, and proper installation, the likelihood of pipe failure, leakage, etc., in new systems is considerably smaller than in old systems. A review of Part 3 on installation procedures will indi cate possible causes of failure in old sewers (e.g., soil move ment, poor bedding, traffic loads, root growth, faulty tap ping for house sewers, etc.) Collapsed sewers and sewers that are badly cracked must be dug up and replaced, but leaking sewers, deterioriated in terior sewer surfaces, and poor joints can be repaired by inplace lining procedures. Lining in place According to the results of the survey of 225 cities men tioned previously, in-place lining of sewers has been prac ticed in more than 20 percent of the communities surveyed, but less than half these cities indicate that lining of sewers was a part of regular maintenance practices. Apparently, in many cities, in-place lining is resorted to when sewer condi tions become intolerable. Types of sewer linings used by surveyed cities include cement-mortar (30 percent of com munities where linings are used), bitumastic (27 percent), special paints (19 percent), and plastics (12 percent). At the time of the survey, in-place lining with epoxy-mort'r had just been introduced. M 50 I WATER AND WASTES ENGINEERING CEMENT-MORTAR LINING After a sewer has been cleaned and removed from ser vice, it can be lined with cement mortar by the same meth od used for lining water mains.24 Sewers so lined have an increased flow capacity because of the smooth, jointless bore and the lower roughness coefficient. Infiltration and root penetration are eliminated and the deteriorated surface restored. One of the difficulties of lining sewers in place is the problem of providing continuous sewer service to an area during the lining operation. This difficulty can, howev er, be overcome. Another method of in-place cement-mortar lining in volves the use of a TV camera and grouting machine in tan dem. This arrangement is used to determine points of leak age and to seal the sewer at those points rather than com plete in-place lining. In large sewers, pressure grouting or pointing may be used. EPOXY-MORTAR LINING The in-place application of an epoxy-mortar lining has been successful in both municipal and industrial sewers. As in in-place cement-mortar lining, the sewer must be re moved from service. The method of application is the same as that described in Part 2, Section 8. PLASTIC LINERS AND ASPHALTIC PAINT The application of plastic liners or asphaltic paints in concrete sewers (as described in Part 2, Section 8) is pos sible if the sewer can be taken out of service. Whatever the method used, lining of pipe in place is quite desirable if in filtration is a sewer problem. Manufacturers Some companies manufacture equipment for the cleaning and/or inspection of sewer systems; other companies sell sewer cleaning and inspecting equipment and also provide cleaning and/or inspection services; still other companies only provide sewer cleaning and/or inspection services. In the following listing, no effort has been made to indicate whether a company produces equipment, provides services, or does both. AAA Pipe Cleaning Co., Cleveland, Ohio Ace Pipe Cleaning, Inc., Kansas City, Mo. American Pipe Services, Minneapolis, Minn. Centriline Div., Raymond International, Inc., New York, N. Y. Certified Laboratories, Ft. Worth, Tex. Champion Corp., Hammond, Ind. Community Utility Equipment & Supplies, Inc., Winter Park, Fla. Flexible, Inc., Culver City, Calif. Flexible Pipe Cleaning Co., South Houston, Texas Halliburton Co., Duncan, Okla. Inspectoline, Inc., College Point, N. Y. Logan Clay Products Co., Logan, Ohio Mainlining Service Co., North Tonawanda, N. Y. Mobile Dredging & Pumping Co., Mobile, Ala. National Chemsearch Corp., Irving, Tex. National Power Rodding Co., Chicago, 111. National Water Main Cleaning Co., Newark, N. J. O'Brien Manufacturing Co., Chicago, III. Ohio Tool and Engineering Co., Springfield, Ohio Penetryn System, Inc., Latham, N. Y. Pilot Manufacturing Co., Torrance, Calif. Robinson Pipe Cleaning Co., Canonsburg, Pa. Sanfax Corp., Atlanta, Ga. Sanitary Hydraulics, Inc., Cleveland, Ohio Solvay Process Div., Allied Chem. Co., New York, N. Y. W. H. Stewart, Inc., Syracuse, N. Y. Turbine Sewer Machine Co., Milwaukee, Wis. Video Pipe Grouting Inc., Chicago, 111. Wayne Manufacturing Co., Pomona, Calif. ED CTD014868 water and wastes /MANUAL of practice number three engineering / AUTHOR'S NOTE As in the case of Manual of Practice No. 2,*` this manual has re ferred to future manuals for the presentation of information and dis cussion of certain matters and items related to the subjects covered Because of space limitations in a manual of this kind, it is necessary to present the material in more than one issue. Therefore, when Manual No. 4 is published, it, together with Manuals No. 2 and 3, will make one unit on the subject of pipes, valves, hydrants, and appurtenances in both water supply and wastewater systems. ACKNOWLEDGMENT In the preparation of this manual, the author consulted more than 40 reference works and articles as well as scores of bulletins, stan dards, and technical information sheets published by individual com panies or pipe producer associations. Acknowledgment is hereby made to the many persons and companies that supplied material and photographic illustrations; acknowledgment is also made to compa nies and associations that granted permission to use some of the data, tables, and diagrams that are included. The author is particularly indebted to the following individuals who reviewed various sections of the manuscript during its preparation. John Autry, manager, sewer pipe, Johns-Manville Corp. R. E. Bald, chief engineer, Pipe Div., International Pipe and Ce ramics Co Richard E. Barnes, managing director, American Concrete Pipe Association. Roger G. Dmig. Jr., manager, technical services, Cast Iron Pipe Research Association. M. H. Ellis, senior marketing specialist, Armco Steel Corp. Kenneth F. Gerlman, vice-president and general manager, National Clay Pipe Institute. William Gonzier, chief engineer, Price Brothers Co. Lewis R. Keyser, engineering manager, Research and Engineering Dept., Price Brothers Co. .John J McCarthy, advertising manager. Pipe Products, Johns-Manville Corp. R. L. Marks, staff engineer, Sewer Pipe Div., Johns-Manville Corp. * . ' j glc' marketing manager, Certain-teed Products Corp. A. J. Reed, president, National Clay Pipe Institute. James M Symons, research public health engineer, Advanced Waste Treatment Branch, Federal Water Pollution Control Admin istration. The author especially acknowledges his indebtedness to his staff c water and wastes engineering for assistance in the preparatic and production of this manual, in particular: Priscilla G. Perlma: associate editor, for editing the manuscript; Josette Trei.chard, a sistant editor, for the production involved in converting manuscrii into printed pages; Linda Greywood, editorial assistant, for prepar tion of the typescript; Carol Gerner, editorial secretary, for handlir the correspondence with contributors and reviewers; and Gordo ,, rjFf,r' rt director, and his staff, for the preparation of the figuri and the layout of the text and illustrations. The author also appri ciates and acknowledges the encouragement and assistance of A Houghton, publisher. REFERENCES ' vSk! NHY.EwiieyJ95f "d S'Wage Trea,rnen''" TM ed,, N* 2. Cohn, M. M., Sewers for Growing America," Ambler Pa Certain-teed Products Corp., l%6 D,cr` ra M 52 I WATER AND WASTES ENGINEERING Dept, of Health, Education, & Welfare, Public Health Service, 1963. 4. Anon. "Clay Pipe Engineering Manual," Costal Lake, 111., Na tional Clay Pipe Inst., 1962. 5. Babbitt, H. E. and Baumann, E. R., "Sewerage and Sewage Treatment," 8th ed., New York, N. Y., Wiley, 1958. 6. Symons, G. E. and Crane, F. W,, Wat. & Sew. Wks. 91: 113 (1944). 7. Symons, J. M,, Wat. & Sew. Wks. 101: 540 (1954). 8. Anon., "Municipal Sewer Ordinances." WPCF Manual of Practice No. 3, Washington. D. C., WPCF, 1949. 9. Anon., "Public Relations for Water Pollution Control," WPCF Publ. No. 12, Washington, D. C., WPCF, 1965. 10. Steel, E. W., "Water Supply and Sewerage," 3rd ed., New York, N. Y., McGraw-Hill, 1953. 11. Anon.. "Location of Underground Utilities," ASCE Manual of Practice No. 14, New York, N. Y,, ASCE, 1937. 12. Stanbery, V. B., "Better Population Forecasts for Areas and Communities," Washington, >. C., Government Printing Office, 1952. 13. Velzy, C. R. and Sprague, J. M., J. Sew . and Ind. Wst. 27: 245 (1955). 14. Harmon, W. G., Eng. News Rec. 80: 1233 (1918). 15. Johnson, W. G., Eng. News Rec., 139: 90 (Oct. 8, 1942). 16. Dittig, R. G., Wat. and Wst. Eng. 4 ( 9): 100 (1967). 17. King. H. 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