Local strain on a leachate collection pipe

Local strain measurements opposite gravel contacts and around a single isolated perforation are reported for a high-density-polyethylene pipe (320 mm outside diameter, 32 mm thick) typical of that commonly used as part of the leachate collection system in municipal solid waste landfills. Emphasis is given to examining the localized effect of coarse gravel contacts on pipe strain and the strain distribution around the perforation. The laboratory testing featured a cylindrical volume of soil with the pipe located in the middle with radially compressive stresses applied along the outer perimeter of the backfill. Two different backfill materials were used. When tested with medium sand backfill the pipe response was essentially uniform, indicative of the near-continuous support and loading provided by the sand. Large variations in local pipe strains were measured with coarse gravel backfill, such as that used in landfill leachate collection systems. Local bending induced by the discontinuous support and loading from the coarse gravel resulted in variations in circumferential and axial strains of over 40%. The local bending effects were not sufficiently large to produce circumferential tension in the pipe tested. A multiplication factor of 1.5 is suggested to account for increases in compressive strain from the coarse gravel. Measurements of surface strain around an isolated 32 mm diameter perforation revealed that a complex three-dimensional response is induced by the presence of the hole. Maximum strains near the hole were found to be 2.7 times larger than those distant from the perforation.