Laboratory tests of small-diameter HDPE pipes buried in reinforced sand under repeated-load

This paper describes laboratory tests on small-diameter high-density polyethylene (HDPE) pipes buried in reinforced sand subjected to repeated loads to simulate the vehicle loads. The amplitude of applied stress was 5.5 kg/cm2 in all tests. Deformation of the pipe was recorded at eight points on the circumference of the tested pipes to measure the radial deformations of the pipe. Also, settlement of the soil surface was measured throughout the test for up to 1000 cycles of loading. These values increased rapidly during the initial loading cycles; thereafter the rate of deformation reduced significantly as the number of cycles increased. The variables examined in the testing program include relative density of the sand, number of reinforced layers, and embedment depth of the pipe. The influence of various reinforced layers at relative densities of 42%, 57%, and 72% in different embedded depths of 1.5–3 times of pipe diameter were investigated. The results show that the percent vertical diameter change (ΔD) and settlement of soil surface (SSS) can be reduced up to 56% and 65% for ΔD and SSS, respectively, by using geogrid reinforcement, and increase the safety of embedded pipes. Also, the efficiency of reinforcement was decreased by increasing the number of reinforcement, the relative density of soil and the embedded depth of the pipe. The influence of the first cycle was also found to be one of the main behavioral characteristics of buried pipes under repeated loads. The ratio of deformation of the pipe from the first cycle to the last cycle changes from 0.5 to 0.9 in different tests. It should be noted that only one type of pipe, one type of geogrid, and one type of sand are used in laboratory tests.