Document N21DVqME7LjZXdYYbveozbr3y

American Water Works Association ANSI/AWWA C401-93 (Revision of ANSI/AWWA C401-83[R86]) AWWA STANDARD FOR THE SELECTION OF ASBESTOS-CEMENT PRESSURE PIPE, 4 IN. THROUGH 16 IN. (100 mm THROUGH 400 mm), FOR WATER DISTRIBUTION SYSTEMS UCAN NATIONAL) STANDARD** Effective date: Nov. 1, 1993. First edition approved by AWWA Board of Directors Jan. 27, 1964. This edition approved Jan. 31, 1993. Approved by American National Standards Institute July 26, 1993. AMERICAN WATER WORKS ASSOCIATION 6666 West Quincy Avenue, Denver, Colorado 80235 AWWA Standard This document is an American Water Works Association (AWWA) standard. It is not a specification. AWWA standards describe minimum requirements and do not contain all of the engineering and administrative information normally contained in specifications. The AWWA standards usually con tain options that must be evaluated by the user of the standard. Until each optional feature is specified by the user, the product or service is not fully defined. AWWA publication of a standard does not constitute endorsement of any product or product type, nor does AWWA test, certify, or approve any product. The use of AWWA standards is entirely voluntary. AWWA standards are intended to represent a consensus of the water supply industry that the product described will provide satisfactory service. When AWWA revises or withdraws this standard, an official notice of action will be placed on the first page of the classified advertising section of Journal AWWA. The action becomes effective on the first day of the month following the month of Journal AWWA publi cation of the official notice. American National Standard An American National Standard implies a consensus of those substantially concerned with its scope and provisions. An American National Standard is intended as a guide to aid the manufacturer, the consumer, and the general public. The existence of an American National Standard does not in any respect preclude anyone, whether that person has approved the standard or not, from manufactur ing, marketing, purchasing, or using products, processes, or procedures not conforming to the stan dard. American National Standards are subject to periodic review, and users are cautioned to obtain the latest editions. Producers of goods made in conformity with an American National Stan dard are encouraged to state on their own responsibility in advertising and promotional materials or on tags or labels that the goods are produced in conformity with particular American National Standards. Caution Notice: The American National Standards Institute (ANSI) approval date on the front cover of this standard indicates completion of the ANSI approval process. This American National Standard may be revised or withdrawn at any time. ANSI procedures require that action be taken to reaffirm, revise, or withdraw this standard no later than five years from the date of publication. Purchasers of American National Standards may receive current information on all standards by calling or writing the American National Standards Institute Inc., 11 W. 42nd St., New York, NY 10036; (212) 642-4900. Copyright 1993 by American Water Works Association Printed in USA li Committee Personnel The AWWA Standards Committee on Asbestos-Cement Pressure Pipe, which reviewed and approved this standard, had the following personnel at the time of approval: Roger C. Graff, Chair Bobby J. Pigg, Secretary Consumer Members R.C. Graff, City of San Diego, San Diego, Calif. R. D. Kennedy, Twentynine Palms Water District, Twentynine Palms, Calif. D. H. Nelson, City of Thousand Oaks, Thousand Oaks, Calif. (AWWA) (AWWA) (AWWA) General Interest Members T.E. Arizumi,* Standards Council Liaison, Hawaii Department of Health, Honolulu, Hawaii KM. Bell, Underwriters Laboratories Inc., Northbrook, 111. T.J. Brown Jr., Factory Mutual Research Corporation, Norwood, Mass. B.R. Elms,* Standards Engineer Liaison, AWWA, Denver, Colo. L.A. Kinney Jr., US Bureau of Reclamation, Denver, Colo. E. W. Misichko.t Underwriters Laboratories Inc., Northbrook, 111. J.S. Rego Jr., Fall River Water Department, Fall River, Mass. E.F. Straw, ISO Commercial Risk Services Inc., Duluth, Ga. (AWWA) (UL) (FMR) (AWWA) (USBR) (UL) (NEWWA) (ISO) Producer Members Marcel Cossette, Ceram-SNA Inc., Sherbrook, Que. S. G. Leyshock, CAPCO Pipe Company Inc., Litchfield, 111. R.H. Novick, CertainTeed Corporation, Englewood, Colo. W.R. Perrell,f CAPCO Pipe Company Inc., Birmingham, Ala. B.J. Pigg, Association of Asbestos-Cement Pipe Producers, Arlington, Va. (AWWA) (AWWA) (AWWA) (AWWA) (AACPP) *Liaison, nonvoting fAltemate iii Contents All AWWA standards follow the general format indicated subsequently. Some variations from this format may be found in a particular standard. SEC. PAGE SEC. PAGE Foreword I Introduction....................................... vi I.A Background....................................... vi I.B History of Standard.......................... vi I. C Acceptance......................................... vi II Special Issues.................................. vii II. A General............................................. vii II.B Type of Pipe.................................... vii III Modification toStandard.................. x IV Major Revisions................................. x V Comments.......................................... x Standard 1 General 1.1 Scope................................................... 1 1.2 References.......................................... 2 1.3 Symbols, Abbreviations, and Definitions................................ 2 1.4 Permeation......................................... 4 2 General Design 2.1 Strength and Design Factors........... 4 2.2 Combined Loading Theory............... 7 2.3 Three-Edge V-Shaped Bearing Load................................................. 8 3 External Loads 3.1 Introduction........................................ 8 3.2 Earth Loads....................................... 8 3.3 Superimposed Loads........................ 18 4 Hydrostatic Pressure 4.1 Introduction...................................... 20 4.2 Static or Working Pressure........... 20 4.3 Surge Pressure................................. 20 5 Design Criteria and Use of Pipe Selection Charts 5.1 Combined Loading Curves.............. 20 5.2 Safety Factors................................. 21 5.3 Use of SelectionCharts......... .......... 21 5.4 Discussion....................................... 21 5.5 Illustrative Problemon Pipe Selection....................................... 37 Appendixes A Friction Loss of Head Chart--Coefficient of Flow, C= 140............................... 38 B Entrapped Air B.l General.............................................. 39 B.2 Entrance of Air............................... 39 B.3 Recommendations to Combat Air Entrapment........................... 40 Figures 1 Classes of Bedding for Conduits in Trench......................................... 5 2 Load-Pressure Curve........................ 7 3 Assembly for Three-Edge V-Shaped Crushing Strength Test.................................................. 8 4 Classification of Construction Techniques............................. 9 5 Values of Cd for Trench Conditions..................................... 11 6 Embankment Conditions............... 12 7 Values of Cc for Positive Projecting Pipe............................. 12 8 Values of Bd/Bc at Which the Trench and Positive Projecting Pipe Equations Give Equal Loads.............................................. 13 9 Values of Cn for Negative Projecting Pipe and Imperfect Ditch Conditions.......................... 14 iv SEC. PAGE 10A Positive Projecting Pipe Projection Ratio p = X --............... -OC 10b Negative Projecting Pipe Projection Ratio p = X ............... &d 11 Projection Ratio p' for the Imperfect Trench Embankment Condition...................................... 16 12 Values of Ct for Tunnel Conditions..................................... 17 13 Superimposed Loads....................... 18 14a Selection Curves for 4-In. Asbestos-Cement Pipe................ 22 14b Selection Curves for 6-In. Asbestos-Cement Pipe................ 23 14c Selection Curves for 8-In. Asbestos-Cement Pipe................ 24 14d Selection Curves for 10-In. Asbestos-Cement Pipe................ 25 14e Selection Curves for 12-In. Asbestos-Cement Pipe................ 26 14f Selection Curves for 14-In. Asbestos-Cement Pipe................ 14g Selection Curves for 16-In. Asbestos-Cement Pipe................ 14A(m) Selection Curves for 100-mm 27 28 Asbestos-Cement Pipe...... 29 14B(m) Selection Curves for 150-mm Asbestos-Cement Pipe...... 30 14c(m) Selection Curves for 200-mm Asbestos-Cement Pipe...... 14D(m) Selection Curves for 250-mm 31 Asbestos-Cement Pipe...... 32 SEC. PAGE 14E(m) Selection Curves for 300-mm Asbestos-Cement Pipe................. 14P(m) Selection Curves for 350-mm Asbestos-Cement Pipe................. 14G(m) Selection Curves for 400-mm Asbestos-Cement Pipe................. 33 34 35 Tables F.l Asbestos-Cement Pipe Type Recommended for Aggressive Internal Water............................ vni F.2 Aggressiveness of Nonsulfate Acidic Soils to AsbestosCement Pipe................................ vm F.3 Chemical Resistance of AsbestosCement Pipe to Neutral (pH = 7.0) Soluble Sulfates in Water and Soils..................... vm F.4 Sulfate Aggressiveness in Water and Soil........................................ ix 1 Recommended Safe Design Values of c for Tunnel Conditions.................................... 16 2 Impact Factors F.......................... 19 3 Values of Load Coefficients Cs for Concentrated and Distributed Superimposed Loads Centered Vertically Over Conduit............. 19 4 Superimposed (Wheel) Load-- Single Wheel = 16,000 lb (7250 kg)...................................... 19 5 Design Internal Pressure and Design External Load................ 36 6 Design External Earth Load........ 36 Foreword This foreword is for information only and is not a part ofAWWA C401. I. Introduction I.A. Background. In 1958 AWWA reactivated its Standards Committee on Asbestos-Cement Pipe, redesignating it as Committee 8340D on Asbestos-Cement Water Pipe. The committee was assigned the task of developing a new document to guide the user in the class selection and installation requirements for asbestoscement pipe. I.B. History of Standard. The standards committee developed AWWA Hand book H2, Standard Practice for the Selection of Asbestos-Cement Water Pipe, which was published in 1964. This handbook covered pipe sizes 4 in. (100 mm) through 36 in. (900 mm). Later in that same year, the standard was redesignated AWWA C401-64 and published under the same title. Subsequent editions of the standard included AWWA C401-77, Standard Practice for the Selection of Asbestos-Cement Distribution Pipe, 4 In. Through 16 In., for Water and Other Liquids; and AWWA C401-83, Standard Practice for the Selection of Asbestos-Cement Distribution Pipe, 4 In. Through 16 In. (100 mm Through 400 mm), for Water and Other Liquids. The 1983 edition was reaffirmed without revision in 1986. I.C. Acceptance. In May 1985, the US Environmental Protection Agency (USEPA) entered into a cooperative agreement with a consortium led by NSF Inter national (NSF) to develop voluntary third-party consensus standards and a certifica tion program for all direct and indirect drinking water additives. Other members of the consortium included the American Water Works Association Research Founda tion (AWWARF), the Conference of State Health and Environmental Managers (COSHEM), the American Water Works Association (AWWA), and the Association of State Drinking Water Administrators (ASDWA). The consortium is responsible for the cooperative effort of manufacturers, regulators, product users, and other inter ested parties that develop and maintain the NSF standards. In the United States, authority to regulate products for use in, or in contact with, drinking water rests with individual states.* Local agencies may choose to impose requirements more stringent than those required by the state. To evaluate the health effects of products and drinking water additives from such products, state and local agencies may use various references, including 1. An advisory program formerly administered by USEPA, Office of Drinking Water, discontinued on Apr. 7, 1990. 2. Specific policies of the state or local agency. 3. Two standards developed under the direction of NSF, ANSIf/NSFt 60, Drinking Water Treatment Chemicals--Health Effects, and ANSI/NSF 61, Drinking Water System Components--Health Effects. *Persons in Canada, Mexico, and non-North American countries should contact the appropriate authority having jurisdiction. tAmerican National Standards Institute, 11 W. 42nd St., New York, NY 10036. $NSF International, 3475 Plymouth Rd., Ann Arbor, MI 48106. vi 4. Other references, including AWWA standards, Food Chemicals Codex, Water Chemicals Codex * and other standards considered appropriate by the state or local agency. Various certification organizations may be involved in certifying products in accordance with ANSI/NSF 61. Individual states or local agencies have authority to accept or accredit certification organizations within their jurisdiction. Accreditation of certification organizations may vary from jurisdiction to jurisdiction. Appendix A, "Toxicology Review and Evaluation Procedures," to ANSI/NSF 61 does not stipulate a maximum allowable level (MAL) of a contaminant for sub stances not regulated by a USEPA final maximum contaminant level (MCL). The MALs of an unspecified list of "unregulated contaminants" are based on toxicity testing guidelines (noncarcinogens) and risk characterization methodology (carcino gens). Use of Appendix A procedures may not always be identical, depending on the certifier. AWWA C401-93 does not address additives requirements. Thus, users of this standard should consult the appropriate state or local agency having jurisdiction in order to 1. Determine additives requirements including applicable standards. 2. Determine the status of certifications by all parties offering to certify prod ucts for contact with, or treatment of, drinking water. * 3. Determine current information on product certification. II. Special Issues II.A. General. The purpose of this standard is to provide guidance in the selec tion of asbestos-cement pressure pipe, manufactured in accordance with ANSI/ AWWA C400 and installed in accordance with ANSI/AWWA C603. In addition to the physical strength parameters addressed in the standard, it is recommended that the user collect site-specific data on water chemistry both for the internal water to be carried by the pipe and external groundwater conditions, and the chemistry of the soil in which the pipe is to be installed. Criteria for various water and soil chemistry parameters that affect asbestos-cement pipe are discussed. " It is the responsibility of the user of an AWWA standard to determine that the products described in that standard are suitable for use in the particular application being considered. II.B. Type of pipe. The following criteria are presented for determining the type of pipe to be used under various soil and water conditions. Each condition should be considered separately even though each may exist in combination with others. These criteria are based on exposures within the temperature range of 40-80F (5-28C). For exposure of pipe to temperatures beyond these limits, consult the manufacturer. The following criteria are referenced as 1. Internal water (Table F.l). 2. External water (Table F.2). 3. Neutral soluble sulfates--internal and external (Table F.3). 4. Acidic soluble sulfates--internal and external. *Both publications available from National Academy of Sciences, 2102 Constitution Ave. N.W., Washington, DC 20418. vii HI. Modification to Standard. Any modification of the provisions, definitions, or terminology in this standard must be provided in the purchaser's specifications. IV. Msgor Revisions. Major revisions to AWWA C401-83(R86) included in this edition of the standard are as follows: 1. Sec. I.C, Acceptance, was added to the foreword. 2. Sec. II.C, Special Issues, was added to the foreword. This section now includes a discussion on criteria for selecting the type of asbestos-cement pipe. This section formerly appeared in the foreword to ANSI/AWWA C400-80 (R86). 3. Sec. Ill, Modification to Standard, was added to the foreword. 4. Sec. 1.4, Permeation, was added. 5. The discussion on water hammer and surge analysis (Sec. B.l through Sec. B.6) was deleted from appendix B and the title of the appendix revised to "Entrapped Air." 6. Appendix C, Functional Power Requirements, was deleted in its entirety. V. Comments. If you have any comments or questions about this standard, please call the AWWA Standards Department, (303) 794-7711, ext. 2201; FAX (303) 794-7310; or write to the department at 6666 W. Quincy Ave., Denver, CO 80235. American Water Works Association A ANSI/AWWA C401-93 (Revision of ANSI/AWWA C401-83[R86]) AWWA STANDARD FOR THE SELECTION OF ASBESTOS-CEMENT PRESSURE PIPE, 4 IN. THROUGH 16 IN. (100 mm THROUGH 400 mm), FOR WATER DISTRIBUTION SYSTEMS SECTION 1: GENERAL Sec. 1.1 Scope This standard has been prepared so that the user may quickly determine the correct pressure classification of asbestos-cement pressure pipe to use under various combinations of internal pressure (working and surge) and external load (earth and superimposed live loads) in water distribution systems. Combined loading curves depicting the relationship between internal pressure and external load capabilities are included to expedite the selection of pipe class, which is defined in ANSI/AWWA C400. Note: Appendix A contains a friction loss of head chart based on the HazenWilliams formula. Appendix B is a discussion of entrapped air. 1.1.1 Pressure classes. Pipe pressure class designations of 100, 150, and 200 refer to the similarly numbered classes listed in ANSI/AWWA C400, Standard for Asbestos-Cement Pressure Pipe, 4 In. Through 16 In. (100 mm Through 400 mm), for Water Distribution Systems. 1 2 AWWA C401-93 1.1.2 Installation. Detailed coverage of the installation of asbestos-cement pipe can be found in ANSI/AWWA C603. Sec. 1.2 References This standard references the following documents. In their latest editions, they form a part of this standard to the extent specified herein. In any case of conflict, the requirements of this standard shall prevail. ASTM* C500--Standard Test Methods for Asbestos-Cement Pipe. ANSIt/AWWA C400--Standard for Asbestos-Cement Pressure Pipe, 4 In. Through 16 In. (100 mm Through 400 mm), for Water Distribution Systems. ANSI/AWWA C403--Standard for the Selection of Asbestos-Cement Transmis sion and Feeder Main Pipe, Sizes 18 In. Through 42 In. (450 mm Through 1050 mm). Design and Construction of Sanitary and Storm Sewers. 1976. Manual of Engi neering Practice No. 37. American Society Civil Engineers, New York. Kerr, S.L. 1948. Practical Aspects of Water Hammer. Jour. AWWA, 40(6):699. Marston, A. 1930. The Theory of External Loads on Closed Conduits in the Light of Latest Experiments. Bull. 96. Iowa State College Engineering Experiment Station. Schlick, W.J. 1940. Supporting Strengths for Cast-Iron Pipe for Water and Gas Service. Bull. 146. Iowa State College Engineering Experiment Station (June 1940). Sec. 1.3 Symbols, Abbreviations, and Definitions Bc = outside diameter of a pipe, in feet (metres). Bd. = width of trench measured at the top of pipe, in feet (metres). BF = bedding factor, which is a load factor correlating three-edge V-shaped bearing test loads to field loads associated with specific bedding conditions. Bt = maximum width of a tunnel excavation, in feet (metres). c = coefficient of soil cohesion, in pounds per square foot (kilonewtons per square metre). Cc = load coefficient for the positive projecting embankment condition. It is a function of the ratio H/Bc, the projection ratio p, and the settlement ratio rsd. Cd = load coefficient for the trench condition. It is a function of the ratio H/Bd and the backfill material. Cn = load coefficient for the negative projecting embankment condition, as well as the imperfect ditch condition. It is a function of the ratio H/Bd, the projection ratio p', and the settlement ratio rsd. Cs = load coefficient for concentrated or distributed superimposed loads. It is a function of the ratio BC/2H and the ratio L/2H for concentrated loads, or the ratio D/2H and the ratio M/2H for distributed loads. Ct = load coefficient for tunnel conditions. It is a function of the ratio H/Bt and the type of soil surrounding the tunnel. American Society for Testing and Materials, 1916 Race St., Philadelphia, PA 19103. tAmerican National Standards Institute, 11 W. 42nd St., New York, NY 10036. A-C DISTRIBUTION PIPE 3 D width of the area over which the distributed superimposed load acts, in feet (metres), F impact factor. H depth of cover, in feet (metres), for all conditions except the tunnel condition. For the tunnel condition, H is the distance from the ground surface to the top of the tunnel excavation, in feet (metres). k Rankine's ratio of lateral earth pressure to vertical pressure, L effective length of the pipe, in feet (metres). For pipe less than 3 ft (1 m), the actual length of the section should be used. For all other lengths, an effective length of 3 ft (1 m) should be used, M length of the area over which the distributed superimposed load acts, in feet (metres). P internal pressure, in pounds per square inch (kilopascals), that the pipe will withstand when no external load exists, Pc concentrated load, in pounds (kilonewtons*). Pd distributed load, in pounds per square foot (kilonewtons per square metre*). Po static or working pressure, which is the maximum anticipated operating pressure in pounds per square inch (kilopascals). Ps surge pressure or water hammer pressure change due to a sudden velocity change, in pounds per square inch (kilopascals). Pt total internal pressure, in pounds per square inch (kilopascals), above which, in combination with some external load Wt applied in three-edge V-shaped bearing, the pipe will withstand, P projection ratio for the positive projecting embankment condition. It is defined as the ratio of the distance that the top of the pipe projects above the original ground surface in feet (metres) to the outside diameter of the pipe in feet (metres). (See Figure 10a.) P' projection ratio for the negative projecting and imperfect ditch condition. It is defined as the ratio of the vertical distance from the original ground surface down to the top of the pipe, in feet (metres), divided by the width of the trench, in feet (metres), for negative projection, and as the ratio of the vertical distance from the top of the excavated trench down to the top of the pipe, in feet (metres), divided by the diameter of the pipe, in feet (metres), for the imperfect ditch condition. (See Figure 10B and Figure 11.) rsd settlement ratio for positive projection, negative projection, and imperfect ditch conditions, SF safety factor. the coefficient of internal friction of backfill material. the coefficient of friction between backfill material and the trench wall. W external load, in pounds per linear foot (kilonewtons per metre), of pipe in the three-edge V-shaped bearing test that the pipe will withstand when no hydrostatic pressure exists. *PC and Pd are loads measured as a mass. However, to use them in equations using SI units, the mass unit must be converted to force by multiplying by 9.807 (g, the acceleration of gravity). 4 AWWA C401-93 We = total earth load, in pounds per linear foot (kilonewtons per metre), to which the pipe is subjected. Ws = total superimposed load, in pounds per linear foot (kilonewtons per metre), of pipe transmitted through the burial environment to the pipe by factors other than the earth loads. Wsc = the concentrated superimposed load, in pounds per linear foot (kilonewtons per metre), of pipe transmitted through the burial environment to the pipe by factors other than the earth loads. Wsd = distributed superimposed load, in pounds per linear foot (kilonewtons per metre), of pipe transmitted through the burial environment to the pipe by factors other than the earth loads. Wt = total external load, in pounds per linear foot (kilonewtons per metre), of pipe applied in three-edge V-shaped bearing above which, in combination with some internal pressure Pt, the pipe will withstand. we = weight of earth, in pounds per cubic foot (kilonewtons per cubic metre*). Sec. 1.4 Permeation The selection of materials is critical for water service and distribution piping in locations where there is likelihood the pipe will be exposed to significant concentra tions of pollutants comprised of low-molecular-weight petroleum products or organic solvents or their vapors. Research has documented that pipe materials such as poly ethylene, polybutylene, polyvinyl chloride, and asbestos-cement; and elastomers, such as used in jointing gaskets and packing glands, may be subject to permeation, by lower-molecular-weight organic solvents or petroleum products. If a water pipe must pass through such a contaminated area or an area subject to contamination, consult with the manufacturer regarding permeation of pipe walls, jointing materi als, and so forth before selecting materials for use in that area. SECTION 2: GENERAL DESIGN Sec. 2.1 Strength and Design Factors The strength of asbestos-cement pressure pipe for water distribution systems must be sufficient to withstand the combined forces of all types of internal pressures (working and surge) and external loadings (earth, live, and impact). Adequate safety factors should be applied to strength requirements to ensure performance under other than ideal or calculated loading conditions. Safety factors are discussed under Sec. 5. 2.1.1 Bedding conditions. The bedding conditions shown in Figure 1 are repre sentative of typical installations. *Density, as used in the equations in this standard, refers to force exerted per unit volume under the acceleration of gravity, rather than mass per unit volume. Where true density is known in pounds per cubic foot, that value should be used in equations using US customary units. Where true density is known in kilograms per cubic metre, it must be converted to newtons per cubic metre by multiplying by 9.807 (g, the acceleration of gravity) before the value is used in equations using SI units. A-C DISTRIBUTION PIPE 5 Concrete cradle, load factor 2.2.3.4 `-8* min (200 mm) ]!), 4" min ^ (100 mm) E' 1 7 B-min - * CLASS A L.'/Xv LL Concrete arch, load factor 2.2.3.4 12 in.ZJ (300 mmlj Carefully compacted backfill 0.6 Bc Shaped bottom with tamped backfill, load factor 1.9 CLASS B Carefully* -compacted granular material Compacted granular bedding, load factor 1.9 Shaped bottom, load factor 1.5, not recommended CLASS C Compacted granular bedding, load factor 1.5 Flat bottom, load factor 1.1, impermissible bedding, not recommended 'Carefully compacted backfill: 95 percent proctor or 70 percent relative density. fLightly compacted backfill: 85-95 percent proctor or 40-70 percent relative density. Note: In rock trench, excavate at least 6 in. (150 mm) below the coupling of the pipe except where concrete cradle is used. Revised and reprinted with permission of ASCE, Manual 37, Design and Constmction of Sanitary and Storm Sewers. 1976. Figure 1 Classes of bedding for conduits in trench 6 AWWA C401-93 2.1.1.1 Class A--concrete-cradle or concrete-arch bedding. This class of bed ding may take either of two forms: 2.1.1.1.1 Concrete cradle. The pipe shall be bedded in a monolithic cradle of plain or reinforced concrete having a minimum thickness of one fourth the inside pipe diameter (minimum of 4 in. [100 mm]) under the barrel and extending up the sides for a height equal to one fourth the outside diameter. The cradle shall have a width at least equal to the outside diameter of the pipe barrel plus 8 in. (200 mm). Backfill shall be compacted above the cradle and extend to 12 in. (300 mm) above the crown of the pipe. The load factor for class A concrete-cradle bedding is 2.2 for plain concrete with lightly compacted (85 to 95 percent proctor or 40 to 70 percent relative density) backfill; 2.8 for plain concrete with carefully compacted (95 percent proctor or 70 percent relative density) backfill; and 3.4 for reinforced concrete with p = 0.4 percent, in which p is the ratio of the area of steel to the area at the invert. 2.1.1.1.2 Concrete arch. The pipe shall be bedded in carefully compacted granular material having a minimum thickness of one fourth the outside pipe diameter (minimum of 4 in. [100 mm]) between barrel and bottom of trench excava tion and extending halfway up the sides of the pipe. The top half of the pipe shall be covered with a monolithic plain or reinforced concrete arch having a minimum thick ness of one fourth the inside diameter (minimum of 4 in. [100 mm]) at the crown and having a minimum width equal to the outside pipe diameter plus 8 in. (200 mm). The load factor for class A concrete-arch-type bedding is 2.8 for plain concrete; up to 3.4 for reinforced concrete with p = 0.4 percent; and up to 4.8 for reinforced concrete with p = 1.0 percent, in which p is the ratio of the area of steel . to the area of concrete at the crown. 2.1.1.2 Class B--first class bedding. Class B bedding may be achieved by either of two construction methods: 2.1.1.2.1 Shaped bottom with carefully compacted backfill. The bottom of the trench excavation shall be shaped to conform to a cylindrical surface with a radius at least 2 in. (50 mm) greater than the radius to the outside of the pipe and with a width sufficient to allow six tenths of the width of the pipe barrel to be bedded in fine granular fill placed in the shaped excavation. Carefully compacted backfill shall be placed at the sides of the pipe to a thickness of at least 12 in. (300 mm) above the top of the pipe. Shaped trench bottoms are difficult to achieve under current con struction techniques. 2.1.1.2.2 Compacted granular bedding with carefully compacted backfill. The pipe shall be bedded in compacted granular material placed on a flat trench bottom. The granular bedding shall have a minimum thickness of one fourth the outside pipe diameter (minimum of 4 in. [100 mm]) and shall extend halfway up the pipe barrel at the side. The remainder of the backfill to a minimum depth of 12 in. (300 mm) over the top of the pipe shall be filled with highly compacted material. 2.1.1.2.3 The load factor for either construction method is 1.9. 2.1.1.3 Class C--ordinary bedding. Class C ordinary bedding may be achieved by either of two construction methods: 2.1.1.3.1 Shaped bottom. The pipe shall be bedded with "ordinary" care in an earth foundation formed in the trench bottom by a shaped excavation that will fit the pipe barrel with reasonable closeness for a width of at least 50 percent of the outside pipe diameter. The side fills and area over the pipe, to a minimum depth of 6 in. (150 mm) above the top of the pipe, shall be filled with lightly compacted fill. The shaped-bottom bedding is not recommended for pipeline construction because it is impractical and costly. A-C DISTRIBUTION PIPE 7 2.1.1.3.2 Compacted granular bedding with a lightly compacted backfill. The pipe shall be bedded in compacted granular material placed on a flat trench bottom. The granular bedding shall have a minimum thickness of 4 in. (100 mm) under the barrel and shall extend one tenth to one sixth of the outside diameter up the pipe barrel at the sides. The remainder of the backfill, to a minimum depth of 6 in. (150 mm) over the top of the pipe, shall be filled with lightly compacted backfill. 2.1.1.3.3 The load factor for either construction method is 1.5. 2.1.1.4 Class D--flat-bottom trench, impermissible bedding. In this class of bedding, the bottom of the trench is left flat, and no care is taken to secure compac tion of backfill at the sides and immediately over the pipe. The load factor for class D bedding is 1.1. 2.1.1.4.1 Class D bedding is not recommended for pipeline construction. Under present construction conditions, class B or C bedding with a compacted granular bedding is generally a more practical and economical method of installation. Sec. 2.2 Combined Loading Theory ' Tests of asbestos-cement pipe under various combinations of internal pressure and external crush load applied in three-edge V-shaped bearing (see Sec. 2.3) shows that there is a relationship between the combined loads at the point of pipe fracture. This relationship can be represented by a parabolic curve as shown in Figure 2. The equation for the load-pressure parabolic curve, which is known as the Schlick for mula, may be expressed as: Wt = wVP pT Eq 1 P represents the internal pressure; W represents the external load. Figure 2 Load-pressure curve 8 AWWA C401-93 Figure 3 Assembly for three-edge V-shaped crushing strength test Sec. 2.3 Three-Edge V-Shaped Bearing Load The combined loading curve shown in Figure 2 is calculated on the basis of crush strengths determined by laboratory tests employing the three-edge V-shaped bearing test method (see ASTM C500 and Figure 3). Because the field-supporting strength of a pipe is influenced by the bedding conditions and by the lateral pres sure acting against the sides of the pipe, it is necessary to apply a bedding load factor to the laboratory three-edge V-shaped bearing loads to correlate them to the actual field loads. Since the external load equals the bedding factor times the V-shaped bearing load, the bedding factor equals the external load divided by the three-edge V-shaped bearing load. Figure 1 shows the load factors to be applied for each bedding class. SECTION 3: EXTERNAL LOADS Sec. 3.1 Introduction For the design of asbestos-cement pressure pipe for water distribution sys tems, external loads Wt are defined by the following equation: Wt We + W, x (SF) BF Eq 2 Sec. 3.2 Earth Loads Earth loads We to which pipe is subjected are a function of the soil density, pipe diameter, depth of cover, and construction techniques employed in laying the pipeline. They depend on the interplay between the weight of the prism of earth directly over the pipe, called the interior prism, and the frictional shearing forces, A-C DISTRIBUTION PIPE 9 plus or minus, transferred to that interior prism by the adjacent outside prisms of earth. The magnitude of earth loads varies with the construction technique employed. There are two major construction techniques normally encountered: trench and embankment. Another technique, the tunnel condition, is not normally found, but has unique design methods that make its inclusion in this discussion necessary. Figure 4 shows these three construction techniques. 3.2.1 Marston's equation. For asbestos-cement distribution pipe design, earth loads are calculated by the general form of Marston's equation: We = CWeBd2 Eq 3 NOTE: In this equation and the following equations, density refers to force exerted per unit volume (pounds per cubic foot or kilonewtons per metre) under the acceleration of gravity, rather than mass per unit volume. Where true density is known in pounds per cubic foot, that value should be used in equations using US customary units. Where true density is known in kilograms per cubic metre, it must Reprinted with permission from ASCE, Manual 37, Design and Construction of Sanitary and Storm Sewers. 1976. Figure 4 Classification of construction techniques 12 AWWA C401-93 edcba abcde aa and bb: The trench width is less than the transition width; earth loads are computed by the trench equation (Eq 4). cc. The trench width is the transition width; earth loads are computed by either Eq 4 or Eq 5. ddand ee: The trench width is greater than the transition width; earth loads are computed by the positive projecting pipe embankment equation (Eq 5). For a given depth of cover, the earth loads resulting from trench widths cc, dd, and ee are equal. Figure 6 Embankment conditions Reprinted with permission from ASCE, Manual 37, Design and Constructtan of Sanitary and Storm Sewers. 1976. Figure 7 Values of Cc for positive projecting pipe A-C DISTRIBUTION PIPE 13 For all trench widths greater than the transition width, earth loads are computed by the positive projecting pipe embankment condition equation (Eq 5). In this latter case and for a given depth of cover, the earth loads are equal to the load that results at the transition width and that is computed by the trench condition equation (Eq 4). (See Figure 6.) 3.2.5.1 The transition width is determined from Figure 8 by multiplying the applicable ratio BdlBc by the applicable pipe outside diameter Bc. The applicable ratio of trench width to pipe outside diameter, BdJBc, can be obtained from Figure 8 for any given ratio of backfill height to pipe outside diameter, H/Bc. 3.2.6 Negative projecting pipe embankment condition. A negative projecting pipe condition is defined as that condition where the pipe is installed in a relatively shallow trench wherein the top of the pipe is at some elevation below the original ground surface. The trench is then backfilled and compacted, and embankment is constructed thereon to finished grade (Figure 4 and Figure 10b). For this condition, Eq.3 is rewritten as: We = CnWeBd2 Eq 7 3.2.6.1 The various values of Cn are obtained from Figure 9. For asbestoscement pipe design, the recommended value for the settlement ratio rsd is zero. The projection ratio p can be determined from the relationships shown in Figure 10b. 3.2.6.2 When calculating earth loads under negative projecting pipe embank ment conditions, consideration must be given to the transition width as defined in kp - kp' = 0.130 = 0 1924 kp - 0.130 Shaded section to enlarged scale 1 2 34 5 1 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 Reprinted with permission from ASCE, Manual 37, Design and Construction of Sanitary and Storm Sewers. 1976. Figure 8 Values of BdlBc at which the trench and positive projecting pipe equations give equal loads 14 AWWA C401-93 Sec. 3.2.5. For values of the ratio Bd/Bc less than those given in Figure 8, the load on a pipe is determined from Eq 7 for negative projecting pipes. However, as the trench width increases and the ratio BdJBc becomes greater than that given in Fig ure 8, the earth load should be determined from Eq 5 for positive projecting pipes. Adherence to the preceding rule will result in the most realistic earth loads for design purposes. 3.2.7 Imperfect trench condition. The imperfect trench condition occurs infre quently and is included for general information only. The imperfect trench embankment condition refers to that construction technique wherein the pipe is first installed as a positive projecting pipe. A portion of the embankment is then built up to some elevation above the pipe top and thoroughly compacted as it is placed. A trench the same width as the pipe is then excavated directly over the pipe down to 0123456780123456 7 8 Coefficient Cn Reprinted with permission from ASCE, Manual 37, Design and Construction of Sanitary and Storm Sewers. 1976. Figure 9 Values of Cn for negative projecting pipe and imperfect ditch conditions Values of A. /-Top of embankment X Be Natural ground. X ^3 _ surface-) A-C DISTRIBUTION PIPE 15 B. /-Top of embankment h____ ** ^Natural ground X\ 1j surface xf |p 11 Figure 10a Positive projecting pipe projection ratio p = Figure 1 OB Negative projecting pipe projection ratio p = -~od or near to its top and subsequently backfilled with loose, compressible material. The remainder of the embankment is then built up to final elevation (Figure 11). For this condition, Eq 3 is rewritten as: We = CnWeBc2 Eq 8 3.2.7.1 The various values of Cn are obtained from Figure 9. For asbestoscement pipe design, the recommended value for the settlement ratio rsd is equal to -0.3. The projection ratio p can be determined from the relationship shown on Figure 11. 3.2.8 Tunnel conditions. There are two types of tunnel construction encoun tered in pipe-laying operation. 3.2.8.1 The first type is the most frequently encountered and occurs when a sleeve of a larger diameter than the specified carrier pipe is first jacked through an embankment. The carrier pipe is then placed into the sleeve without becoming an integral part of the tunnel construction. The sleeve supports the entire earth load and the carrier pipe is not subjected to crushing loads. When selecting the required pipe classification for this condition, only the internal pressure needs to be consid ered for design. 3.2.8.2 The second type of tunnel condition is rarely encountered in distribu tion pipe work but occurs when the carrier pipe itself must carry the external load. The area through which the pipeline must pass is bored and may be braced with supports. The carrier pipe is then placed in the tunnel, and the space between the pipe and tunnel braces backfilled with compacted earth, grout, or concrete. Once this operation is completed, the earth load automatically transfers from the tunnel sup ports to the carrier pipe itself. For this condition, Eq 3 is rewritten as: We = CtBt (weBT - 2c) Eq 9 3.2.8.3 Values of Ct for different types of soil are obtained from Figure 12. If the value for the coefficient of cohesion is not available from laboratory tests, then the recommended safe design values in Table 1 are to be used. 16 AWWA C401-93 Projection ratio, p' = 4B~e Top of embankment / fSHsiSSS Compressible backfill Top of stage < construction compacted fill / Trench dug in compacted fill Natural ground / % Figure 11 Projection ratio p' for the imperfect trench embankment condition Table 1 Recommended safe design values of c for tunnel conditions Materials Clay, very soft Clay, medium Clay, hard Sand, loose dry Sand, silty Sand, dense Top soil, saturated Values of c lb/ft2 (kN/rn2) 40 250 1000 0 100 300 100 (1.63) (10.19) (40.77) (0) (4.007) (12.23) (4.007) 3.2.8.4 When the tunnel excavation becomes excessive, or when the space sur rounding the pipe or tunnel lining is not carefully filled, or when the cohesion of the undisturbed material above the tunnel construction is destroyed by soil saturation or vibration, the earth load should be calculated using Eq 4 for trench conditions. It is difficult to determine that the tunnel excavation is excessive. Therefore, it is rec ommended that Eq 4 be used. Values of H /B A-C DISTRIBUTION PIPE 17 01 2 345 Values of coefficient C j Reprinted with permission from ASCE, Manual 37, Design and Constmction of Sanitary and Storm Sewers. 1976. Figure 12 Values of Ct for tunnel conditions 18 AWWA C401-93 Sec. 3.3 Superimposed Loads Superimposed or live loads Ws are external loads (other than the normal earth loads) transmitted to the pipe. There are two types of superimposed loads as illus trated in Figure 13: (1) concentrated Wsi and (2) distributed Ws2. 3.3.1 Concentrated loads. A concentrated load is a load caused by a single force, which may be either static or dynamic in nature. Vehicular wheel loads are the most frequently encountered concentrated loads. The magnitude of the load pro duced by concentrated superimposed forces is determined by: TWTrsc = C--sP-c--F Eq 10n (see Tables 2 and 3) 3.3.2 Distributed load. A distributed load is a load caused by a uniform force distributed equally over a given area. The load may be either static or dynamic in nature. The magnitude of the load produced by distributed forces is determined by: Wsd = CsPdFBc Eq 11 (see Table 4) Unit load tVsi from superimposed concentrated live load Figure 13 Superimposed loads Table 2 Impact factors F Depth of Cover--ft (m) 1.0-2.0 (0.3-0.6) 2.0-3.0 (0.6-1.0) 3.0 or greater (1.0 or greater) Impact Factor F 1.2 1.1 1.0 A-C DISTRIBUTION PIPE 19 Table 3 Values of load coefficients Cs for concentrated and distributed superimposed loads centered vertically over conduit Pipe Size in. (mm) 4 (100) 6 (150) 8 (200) 10 (250) 12 (300) 14 (350) 16 (400) Depth of cover--ft (m) 2 (0.61) 0.105 0.147 0.191 0.237 0.279 0.317 0.354 2.5 (0.76) 0.076 0.106 0.137 0.174 0.202 0.232 0.259 3 (0.91) 0.055 0.078 0.102 0.129 0.153 0.175 0.197 4 (1.22) 0.033 0.046 0.061 0.078 0.092 0.106 0.121 5 (1.52) 0.022 0.031 0.041 0.052 0.062 0.071 0.081 6 (1.83) 0.016 0.023 0.029 0.037 0.044 0.050 0.057 8 (2.44) 0.009 0.013 0.017 0.022 0.025 0.030 0.034 10 (3.05) 0.006 0.008 0.010 0.013 0.016 0.018 0.021 12 (3.66) 0.004 0.006 0.008 0.009 0.011 0.013 0.015 16 (4.87) 0.002 0.003 0.004 0.006 0.007 0.008 0.009 20 (6.09) 0.0015 0.002 0.003 0.0035 0.004 0.005 0.0055 Table 4 Superimposed (wheel) load--single wheel = 16,000 lb (7250 kg) Pipe Diameter--in. (mm) Cover Over Top of Pipe ft (m) 6 (150)* 8 (200) 10 (250) 12 (300) Wheel Load--lb !ft (kN/m) 2 (0.61) 2.5 (0.76) 3 (0.91) 4 (1.22) 5 (1.52) 6 (1.83) 8 (2.44) 10 (3.05) 12 (3.66) 16 (4.87) 20 (6.09) 797 (11.6) 693 (10.1) 425 (6.20) 256 (3.73) 176 (2.56) 149 (2.17) 69 (1.00) 43 (0.63) 37 (0.54) 21 (0.39) 5 (0.07) 932 (13.6) 907 (13.2) 544 (7.93) 331 (4.83) 218 (3.18) 197 (2.87) 91 (1.33) 59 (0.86) 48 (0.70) 27 (0.39) 11 (0.16) 1272 (18.5) 1076 (15.7) 693 (10.1) 421 (6.14) 277 (4.04) 245 (3.57) 112 (1.63) 74 (1.08) 53 (0.77) 32 (0.47) 16 (0.23) 1488 (21.7) 1167 (17.0) 816 (11.9) 490 (7.15) 330 (4.81) 235 (3.43) 139 (2.03) 85 (1.24) 59 (0.86) 37 (0.53) 21 (0.30) For 4-in. (100-mm) pipe, use same value as for 6-in. (150-mm) pipe. 14 (350) 1691 (24.7) 1237 (18.0) 933 (13.6) 565 (8.24) 378 (5.51) 267 (3.89) 160 (2.33) 96 (1.40) 69 (1.01) 43 (0.62) 26 (0.38) 16 (400) 1888 (27.5) 1382 (20.2) 1048 (15.3) 645 (9.41) 432 (6.30) 304 (4.44) 181 (2.64) 112 (1.63) 80 (1.17) 48 (0.70) 29 (0.42) SECTION 4: HYDROSTATIC PRESSURE Sec. 4.1 Introduction For the design of asbestos-cement pressure pipe for water distribution sys tems, the internal hydrostatic pressure Pt is defined by: Pt = (Po+Ps)SF Eq 12 SF is the design safety factor. For asbestos-cement pressure pipe for water distribution systems, a safety factor of 4 is recommended when surge or water ham mer is not calculated and added to operating pressure. 20 AWWA C401-93 Sec. 4.2 Static or Working Pressure The static or working pressure may be induced by pumps, gravity (such as the bead created by a reservoir or elevated water tank), or a combination of both pumps and gravity. Under a 100 percent gravity situation, the pressure in the line at a given point is somewhat higher when there is no flow and conditions are static. Under static conditions, the pressure at a given point, measured in feet (metres) of head, is equal to the difference between the elevation of that point and the water surface level at the reservoir. Under flowing conditions, the pressure at a given point is reduced by the amount of friction and other energy losses resulting from the flow of water from the reservoir to that point. The magnitude of this head loss may be found by using the Hazen-Williams chart in appendix A. In piping systems that have long runs with relatively few fittings and accessories, the recommended value of C (coefficient of flow) is 140. Sec. 4.3 Surge Pressure Surge pressures Ps are of a transient nature and are caused by unsteady or changing conditions in the pipeline. The terms water hammer, surge, or transient pressure are often used interchangeably to refer to these pressures, which are of brief duration but can be of considerable magnitude. A variety of conditions may cause surge pressures. These include a valve opening or closing, sudden movement of air in a line, or a pump starting or stopping. Surge pressures in a distribution system can be of considerable magnitude, particularly when fire hydrants are rapidly opened or closed. The magnitude of this surge is difficult to determine and depends on the speed at which the fire hydrant is opened or closed. Design criteria for asbestos-cement pressure pipe for water distribution systems incorporate a safety factor of 4 in the operating or pressure class of the pipe to allow for an unknown amount of surge pressure that will occur in the system. Appendix B of ANSI/AWWA C403 presents a discussion of surge pressures and how they may be controlled. SECTION 5: DESIGN CRITERIA AND USE OF PIPE SELECTION CHARTS Sec. 5.1 Combined Loading Curves Extensive testing and application of statistical analysis have shown that the strength characteristics of asbestos-cement pipe conform to the principles of the combined loading theory developed by the late W.J. Schlick. This theory, commonly discussed in terms of the Schlick formula represented graphically as a parabola, is used as the basis for the design and class selection of asbestos-cement pressure pipe for water distribution systems. (See Figures 14a through 14g and Figures 14A[m] through 14G[m].) 5.1.1 Curve development. The families of selection curves in this standard were developed using the Schlick formula that establishes a functional relationship between external load and internal pressure. The external and internal load inter cepts are tabulated in Table 5 (page 36). / A-C DISTRIBUTION PIPE 21 Sec. 5.2 Safety Factors In distribution pipes, the effect of water hammer generated by the opening and closing of fire hydrants can be of significant magnitude because of the high velocities generated by open hydrant flow conditions on small-diameter lines in distribution systems. It is difficult to accurately evaluate the magnitude of surges, and if calcu lated, it would be impractical to attempt to control the surge by the use of surge tanks or other devices. Rather than employ a rule-of-thumb surge allowance based on an assumed velocity change, a safety factor of 4 is applied to the class pressure rating (see ANSI/AWWA C400 for defining parameters) of the pipe to account for undetermined surges. 5.2.1 Design criteria. The design criteria for asbestos-cement pressure pipe for water distribution systems is based on a design point on the combined loading para bolic curve where the following minimum conditions are met: (1) a safety factor of 4 times the pressure class of the pipe, and (2) a safety factor of 2.5 times the threeedge V-shaped bearing equivalent of an earth load calculated as 5 ft (1.52 m) depth of cover, a trench width equal to pipe inside diameter plus 2 ft (0.6 m) (or a positive projecting conduit condition if lesser), a soil density of 120 lb/cu ft (19 kN/m3), and class C bedding condition. Sec. 5.3 Use of Selection Charts The scales are correlated to the three-edge V-shaped bearing equivalent of 2.5 times the earth load calculated using a soil density of 120 lb/cu ft (19 kN/m3) and a trench width equal to the inside diameter (ID) of the pipe plus 2 ft (0.6 m) (or the positive projecting conduit condition if lesser). 5.3.1 Design earth loads. Table 6 gives the design earth load values, which are obtained by calculating the external earth load based on a trench width equal to the ID of the pipe plus 2 ft (0.6 m) (or the positive projecting conduit condition if lesser). The earth load is then divided by the appropriate bedding factor for the class of bedding and multiplied by a safety factor of 2.5. The design earth load values from Table 6 can then be used to enter the selection curve charts using the design exter nal load values given at the top of the selection curve charts. When there is an external condition that warrants the consideration of all external loading factors and/or a change in the safety factor, the equivalent external load should be deter mined and the selection chart entered at the proper value of the design external load scale found at the top of the chart. Sec. 5.4 Discussion ANSI/AWWA C403 contains information similar to that contained herein but deals with larger diameter pipes. In ANSI/AWWA C403, the class selection is based on evaluation of all design conditions, including surge pressures. Adequate factors of safety are applied to the combination of loads to which the pipeline will be subjected. The primary differences between AWWA C401 and ANSI/AWWA C403 are dif fering methods of designing pipelines to account for internal and external load conditions. In the smaller sizes covered by AWWA C401, surge pressures can be of great magnitude and are difficult to predict or control in design. In the larger sizes covered in ANSI/AWWA C403, the design is based on an evaluation of surge pres sure, which can be controlled in design. Calculated surge pressure is added to operating pressure before a safety factor of 2 is applied. For external loads, AWWA 22 AWWA C401-93 Design External Load-lb./lin.ft. O perating P ressure-psi Design P ressure-psi Figure 14a Selection curves for 4-in. asbestos-cement pipe Design External Load-lb/lin ft A-C DISTRIBUTION PIPE 23 O perating P ressure-psi Design P ressure-psi Figure 14B Selection curves for 6-in. asbestos-cement pipe 24 AWWA C401-93 Design External Load-lb/lin ft O perating P ressure-psi Design P ressure-psi Figure 14c Selection curves for 8-in. asbestos-cement pipe A-C DISTRIBUTION PIPE 25 Design External Load-lb/lin ft 2,000 4,000 6,000 8,000 10,000 250 --1-- ------ 1------ ------ 1------ ------ 1------ ------ 1------ 1,000 200 800 Design P ressure-psi W3(<aai0/>>. O) c Oa 100 Class 150\ Class IOoN. Class 200 N. -- 50 600 400 \-- 200 c .*>2* o ____ 1____ ____ 1____ \__ 1____ ____ 1____ 1 15co 2.5 5 OB CCTI 8 1 12 16 20 1 11 o5 2.5 5 8 12 16 20 " CO C ___1____ L____ 1_____ 1___LJ_______________________ Depth of Cover-ft Figure 14d Selection curves for 10-in. asbestos-cement pipe 26 AWWA C401-93 Design External Load-lb/lin.ft. Design P ressure-psi Figure 14e Selection curves for 12-in. asbestos-cement pipe Design External Load-lb/lin ft A-C DISTRIBUTION PIPE 27 O perating Presure-psi Design P ressure-psi Figure 14F Selection curves for 14-in. asbestos-cement pipe 28 AWWA C401-93 Design External Load-lb/lin ft O perating P ressure-psi Design P ressure-psi Figure 14g Selection curves for 16-in. asbestos-cement pipe A-C DISTRIBUTION PIPE 29 Design External Load-kN/m 0 20 30 50 60 70 O perating Pressure-kPa Design Pressure-kPa Figure 14A(m) Selection curves for 100-mm asbestos-cement pipe O perating Pressure-kPa Design Pressure-kPa 30 AWWA C401-93 Design External Load-kN/m 0 10 20 30 40 50 60 70 80 Figure 14B(m) Selection curves for 150-mm asbestos-cement pipe A-C DISTRIBUTION PIPE 31 Design External Load-kN/m 0 25 50 75 100 125 150 O perating Pressure-kPa Design Pressure-kPa Figure 14c(m) Selection curves for 200-mm asbestos-cement pipe 32 AWWA C401-93 Design External Load-kN/m O perating Pressure-kPa Design Pressure-kPa Figure 14D(m) Selection curves for 250-mm asbestos-cement pipe Design External Load-kN/m A-C DISTRIBUTION PIPE 33 O perating Pressure-kPa Design Pressure-kPa Figure 14E(m) Selection curves for 300-mm asbestos-cement pipe 34 AWWA C401-93 Design External Load-kN/m Design Pressure-kPa Figure 14F(m) Selection curves for 350-mm asbestos-cement pipe Design External Load-kN/m A-C DISTRIBUTION PIPE 35 O perating Pressure-kPa Design Pressure-kPa Figure 14G(m) Selection curves for 400-mm asbestos-cement pipe 36 AWWA C401-93 Table 5 Design internal pressure and design external load* Class 100 Class 150 Class 200 Nominal Pipe Size Internal Pressure External Load Internal Pressure External Load Internal Pressure External Load in. (mm) psi (kPa) Ib/lin. ft (kN/m) psi (kPa) lb!tin. ft (kN/m) psi (kPa) Ib/lin. ft (kN/m) 4 (100) 6 (150) 8 (200) 10 (250) 12 (300) 14 (350) 16 (400) 417 (2900) 441 (3000) 472 (3300) 490 (3400) 490 (3400) 500 (3400) 500 (3400) 4100 4000 4000 4400 5200 5200 5800 (60) (58) (58) (64) (76) (76) (85) 616 (4200) 632 (4400) 653 (4500) 650 (4500) 658 (4500) 650 (4500) 654 (4500) 5400 5400 5500 7000 7600 8600 9200 (79) (79) (80) (102) (111) (126) (134) 809 (5600) 815 (5600) 824 (5700) 826 (5700) 830 (5700) 826 (5700) 825 (5700) 8700 9000 9300 11,000 11,800 13,500 15,400 (127) (136) (136) (161) (172) (197) (225) *It is necessary to apply a load factor to the three-edge bearing loads obtained in the crushing tests in order to correlate them to the field loads. Table 6 Design external earth load ripe oize in. (mm) 4 (100) 6 (150) 8 (200) 10 (250) 12 (300) 14 (350) 16 (400) H 2.5 ft (0.76 m) 290 (4.23) 390 (5.69) 490 (7.15) 590 (8.61) 670 (9.78) 740 (10.80) 800 (11.68) H 5.0 ft (1.52 m) 610 840 1070 1330 1550 1760 1960 (8.90) (12.26) (15.62) (19.41) (22.62) (25.69) (28.60) HH 2.5 ft (0.76 m) 5.0 ft (1.52 m) in. (mm) 4 (100) 6 (150) 8 (200) 10 (250) 12 (300) 14 (350) 16 (400) 370 500 620 750 850 940 1010 (5.40) (7.30) (9.05) (10.95) (12.40) (13.72) (14.74) 770 1060 1360 1690 1970 2240 2490 (11.24) (15.47) (19.85) (24.66) (28.75) (32.69) (36.34) Class B Bedding H 8.0 ft (2.44 m) H 12 ft (3.66 m) W--lb/ft (kN/m) 980 1380 1770 2220 2610 2860 2980 (14.30) (20.14) (25.83) (32.40) (38.09) (41.74) (43.49) 1490 2090 2710 3230 3550 3810 4030 (21.74) (30.50) (39.55) (47.14) (51.81) (55.60) (58.81) Class C Bedding H 8.0 ft (2.44 m) H 12 ft (3.66 m) W--lb/ft (kN/m) 1250 1740 2250 2820 3310 3620 3770 (18.24) (25.39) (32.84) (41.15) (48.31) (52.83) (55.02) 1890 2650 3430 4090 4500 4820 5100 (27.58) (38.67) (50.06) (59.69) (65.67) (70.34) (74.43) H 16 ft (4.88 m) H 20 ft (6.10 m) 1990 (29.04) 2800 (40.86) 3380 (49.33) 3730 (54.44) 4120 (60.13) 4520 (65.96) 4990 (72.82) 2500 (36.48) 3360 (49.04) 3770 (55.02) 4170 (60.86) 4620 (67.42) 5000 (72.97) 5250 (76.62) HH 16 ft (4.88 m) 20 ft (6.10 m) 2530 (36.92) 3550 (51.81) 4280 (62.46) 4730 (69.03) 5220 (76.18) 5730 (83.62) 6320 (92.23) 3170 (46.26) 4250 (62.02) 4780 (69.76) 5290 (77.20) 5850 (85.37) 6330 (92.38) 6650 (97.05) A-C DISTRIBUTION PIPE 37 C401 considers only earth loads and a recommended safety factor of 2.5 is applied. In ANSI/AWWA C403, both earth loads and live loads are added before a factor of safety of 1.5 is applied to the combination of these external loads. In summary, ANSI/AWWA C403 design is based on a more detailed evaluation of the magnitude of surge pressure and live loadings, and factors of safety based on this more precise knowledge of actual operating conditions are applied. Sec. 5.5 Illustrative Problem on Pipe Selection The application of the curves to design is shown in the following problem: Required: A 6-in. pipe to operate at a pressure of 120 psi at 8 ft depth of cover, bedding condition class C, soil weight 120 lb/cu ft. Solution: Enter the selection curve for 6-in. pipe at bedding condition class C, 8-ft cover. The intersection of the 8-ffc cover line with the 120-psi operating pressure line falls between pipe classes 100 and 150. Use 6-in., class 150. The intersection of the 8-ft cover line with the class 150 curve is at 140-psi operating pressure, or 560-psi design pressure. Therefore, the pressure safety factor equals 560/120 = 4.66, with a safety factor of 2.5 for external earth load. APPENDIX A Friction Loss of Head Chart--Coefficient of Flow, C = 140 This appendix is for information only and is not a part ofAWWA C401. 0 tr >, 0 03 -R E o 0 3= g 0 0 = CD O .> SZ O Q_ 4Eo= OTf. 03 3 E O) II II I ooo coo ic-o icno *-- CM CO O =i 0o 5 0 O 0S 00 E 0 m- 0 bEtLt.oU. O fc090Oc) O TJ 0 r 0> t0o E -;Q> O II O I O o CO CO o ^ t 0) 03 -Q 0 J2 o 0 a0= *oC2) 8t l! O *= 0 11 03 O o o .E 0 5 il 0_3 O 0 o ~>o _O 0C 0 2 to ^T> p t0: >, 0 .Q UJ 0 C 5 oo zO 0 O 5= ./ il ii i ooo II II II I oooo oooo in n co 00 '9q-. 20 r- o .9 ~| 0 & 03 O ^ 3 E *0 E 0 u X^_0I -0Q -gE ^3 > o 00 'F 0C 0 E >s o t So 0 3~ O l "O 0 0 o 8c0 m."O 0 c QOC0 c 0 CO N 0 CO . X 0 ^ :sE o Q0 .00 O o 3 *o 00 *~ O .e 03 C a II o o Q. E o o o 0 0 C 3 '0 0 O E 3 O* 03 c 0 'o 0 o c 0c Q. 0 0 o 0N Q- E 0 O o 0 0 s0z 'o. O 0 x C >> T 0 'o E 0 ? 00 Q. 0 0 O? E 0 Pipe Diameter, Inches seijdui `jajeujeia ady 38 140 be Loss of Head in Feet Per Thousand Feet of Length APPENDIX B Entrapped Air This appendix is for. information only and is not a part ofAWWA C401. SECTION B.1: GENERAL Air entrapment in pipelines can cause serious operational difficulties, including reduction in capacity because of reduced cross-sectional area and fluctuation in flow caused by expanding and contracting air in the line. These fluctuations in flow cause sudden movements of the air from one location to another, followed by slugs of water, and this can cause serious surges. SECTION B.2: ENTRANCE OF AIR Air can enter a pipeline in many ways, not always through the intake. Entry may be caused by the release of air from water due to temperature and pressure variation, by draining the line, or by draining parts of the line during normal shut down. Negative surges may cause air to enter at air valves. Air should be prevented from entering the line to reduce operational difficulties. Suggested solutions for con trol are as follows: 1. Intake. Correct design procedures, including provision for low water-level pump cutoff. 2. Release of air. Air is entrained in the water at the intake and its release cannot be prevented. However, the quantities are usually not large and air valves can be used to remove the air. There are various types of air valves with different functions, and the selection of the proper type and location for installation is essential. 3. Draining the pipeline. Air must be allowed to enter the pipeline when the pipe is drained. Large-orifice air valves should be provided for exhausting the air from the pipeline during refilling. Draining and then refilling does not often occur; therefore, long filling times may be satisfactory. 4. Drainage during shutdown. This can be a serious problem. Open stand pipes can be provided for air entry and exhaust. 39 40 AWWA C400-93 SECTION B.3: RECOMMENDATIONS TO COMBAT AIR ENTRAPMENT Colorado State University* has conducted studies to determine the effect of air entrapment in pipelines. The results of the studies proved that suddenly released entrapped air, under apparently static conditions, creates a situation similar to that of classic water hammer. Pressures are generated that may be on the order of 15 times the pipeline test pressure. Any pipeline material is seriously affected by this rapid magnitude of load increase. Hydrostatic failure may be traced to suddenly released entrapped air. The initial filling and testing of a pipeline is often the most critical period of its service life. Recommendations made to combat air entrapment are as follows: 1. Pipeline should be laid to grade wherever possible. 2. Automatic, continual-acting, air-release valves should be used at all high points. 3. Air should be slowly bled from pipeline. 4. Filling velocity in the pipeline should be limited to 1 ft/sec (0.3 m/s) or less. 5. Use d/D = 1/10 to 1/100. Where: d = diameter of air release valve D = pipe diameter Colorado State University, Fort Collins, Colo. This page intentionally blank. 3P-3C-43401 -11/97-MG Printed on recycled paper.