This concrete-encased duct bank assembly is installed within undisturbed earth with a minimum twenty-four inch cover to finished grade or paving substrates. The conduits are bedded within a minimum three-inch cover of twenty-five hundred psi twenty-eight day three-eighths inch aggregate concrete and separated using plastic spacers for multiple duct runs. Fluidized thermal backfill with a thermal resistivity value of less than ninety rho fills the trench surrounding the concrete encasement. Foil-backed marker tapes are installed sixteen inches maximum on center on each side above the concrete encasement.
24" UNDISTURBED EARTH FINISHED GRADE & SUBSTRATES(S) AS SHOWN FINISHED PAVING & SUBSTRATES(S) AS SHOWN FOIL-BACKED MARKER TAPES, 16" MAX OC., ONE AT EACH SIDE. PROVIDE 3" MIN COVER OF 2500PSI (28 DAYS) 3/8" AGGREGATE CONCRETE. PROVIDE PLASTIC SPACERS FOR MULTIPLE DUCT RUNS 3" MIN 10.76 MIN 3" MIN 3" MIN FLUIDIZED THERMAL BACKFILL (TO PROVIDE THERMAL RESISTIVITY VALUE OF LESS THAN 90 RHO) 3" MIN
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