The Beneficial Use of Flowable Backfill Around Concrete Pipes

Flowable backfill around pipes offers a number of advantages compared to the placement of earth fill. It does not require compaction, is faster to place, and flows into the pipe haunches. In addition, flowable backfill may in some cases reduces the earth load on the pipe. A finite element analysis shows the effects of geometry, subsurface condition and relative stiffness on the earth load. Cost comparisons often favor flowable backfill. A case history where flowable backfill has been proposed around a 36 inch concrete spillway pipe beneath 260 feet of fly ash fill shows lesser loads that permit use of a pipe of reduced wall thickness.