Designation:D2774−12StandardPracticeforUndergroundInstallationofThermoplasticPressurePiping1ThisstandardisissuedunderthefixeddesignationD2774;thenumberimmediatelyfollowingthedesignationindicatestheyearoforiginaladoptionor,inthecaseofrevision,theyearoflastrevision.Anumberinparenthesesindicatestheyearoflastreapproval.Asuperscriptepsilon(´)indicatesaneditorialchangesincethelastrevisionorreapproval.INTRODUCTIONIngeneral,thermoplasticspressurepipingmaterialsbehaveasductilematerialsunderload,meaningthattheycanundergoconsiderabledeformationwithoutdamage.Pipingmadefromsuchmaterialshastheabilitytobendunderaloadwithoutbreakingandtodeforminotherways,whileofferingcontinuedresistance.Thisflexibilityallowsductilethermoplasticpipetoactivatethroughpipedeformationlateralsoilforceswhichcreateapipe/soilsystemcapableofsafelysupporting–eveninpipessubjecttolittleornointernalpressure–theearthandsuperimposedloadswhichareencounteredinmostpipeinstallations.However,properinstallationtechniquesarerequiredtoensurethatthenecessarysupportatthebottomandpassivesoilpressuresatthesidesofthepipearedevelopedandmaintained.Soilsinwhichtrenchesaredugshallbeexaminedandidentifiedandthetrenchespreparedandbackfilledinaccordancewithsoundbeddingproceduresandthispractice.1.Scope*1.1ThispracticegovernsproceduresandreferencesASTMspecificationsforundergroundinstallationofthermoplasticpressurepiping,63-in.(1372-mm)nominalsizeandsmaller.Itisbeyondthescopeofthispracticetodescribetheseproce-duresindetailsinceitisrecognizedthatsignificantdifferencesexistintheirimplementationdependingonkindandtypeofpipematerial,pipesizeandwallthickness,soilconditions,andthespecificenduse.1.1.1Thispracticeassumesthatovertherangeofantici-patedoperatingconditions,includingmaximumexternalload-ingandminimuminternalpressure,thesoil/pipesystemwilloffersufficientstructuralstabilitytoresistpossibleexcessivediametricaldeformation,orevencollapse.Incases,particu-larlywithlargediameterthinner-walledpipe,forwhichthevalidityofthisassumptionmaybe...
