Biaxial Testing to Investigate Soil-Pipe Interaction of Buried Fiber-Reinforced Cement Pipe

Abstract

Three tests were performed to develop baseline information on the behavior of fiber-reinforced cement (FRC) pipe under biaxial loading. Pipes were instrumented to measure circumferential strains at various locations around the circumference and to capture changes in vertical and horizontal pipe diameter. The first two tests examined the response of wet and dry pipes under conditions simulating steadily increasing overburden pressure in an embankment loading condition, reaching earth pressures equivalent to more than 15 m. The third test examined the time-dependent response of a second, wet pipe under sustained pressure of 180 kPa. Elastic soil-pipe interaction theory shows that increases in pipe deformation lead to a redistribution of loads to the surrounding ground and reductions in bending moments. Preliminary calculations for the three pipe tests indicated that, even in the low modulus backfill, the pipe deformations were sufficient to reduce applied earth pressures on the pipes and the bending moments within them. These pipes exhibited semirigid behavior, in which bending moments were reduced below levels experienced by a rigid pipe. Bending moment decreases were greater for the wet pipe than for the dry pipe because the wet specimens had lower manufactured wall thickness and wet FRC has a lower modulus. Reductions in the modulus of the FRC material were estimated to decrease moments by approximately 30% by the end of the 50-h time period of the third test and by approximately 36% at the peak overburden pressure (300 kPa) reached during the second test.