Local strain on a leachate collection pipe

Local strain measurements opposite gravel contacts and around a single isol ated 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 t esting featured a cylindrical volume of soil with the pipe located in the m iddle with radially compressive stresses applied along the outer perimeter of the backfill. Two different backfill materials were used. When tested wi th medium sand backfill the pipe response was essentially uniform, indicati ve of the near-continuous support and loading provided by the sand. Large v ariations in local pipe strains were measured with coarse gravel backfill, such as that used in landfill leachate collection systems. Local bending in duced by the discontinuous support and loading from the coarse gravel resul ted in variations in circumferential and axial strains of over 40%. The loc al bending effects were not sufficiently large to produce circumferential t ension in the pipe tested. A multiplication factor of 1.5 is suggested to a ccount for increases in compressive strain from the coarse gravel. Measurem ents of surface strain around an isolated 32 mm diameter perforation reveal ed 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 t han those distant from the perforation.