The performance of a laboratory facility for evaluating the structural response of small-diameter buried pipes

Abstract

The performance of a new laboratory facility for testing small-diameter buried pipes (less than 300 mm diameter) subject to the biaxially compressive earth pressures expected to prevail under deep and extensive overburden is examined. The new facility consists of a prism of soil 2.0 m wide × 2.0 m long × 1.6 m high contained within a stiff steel structure. Laboratory tests were performed in the new test facility to examine the appropriateness of the boundary conditions imposed during testing. Overburden pressures are successfully simulated with a pressurized air bladder. Boundary friction was limited to only minimal effects with lubricated polyethylene sheets. The stiffness of the lateral boundary is sufficiently large to induce lateral stresses close to those for zero lateral strain conditions. Overall, the effects on the pipe arising from the idealizations involved in the laboratory model were found to be small. The application of the new test cell is illustrated by using it to assess the response of a small-diameter landfill leachate collection pipe under two different backfill conditions. This comparison showed that the structural response of the pipe is significantly impacted by the coarse gravel backfill used in landfill drainage layers. Maximum pipe deflections and strains were nearly twice as large when tested in the coarse gravel compared with the sand backfill. Much greater variations of deflection and strain were also measured with the coarse gravel when compared with the sand backfill due to local bending effects from the coarse gravel.Key words: buried pipes, soil-structure interaction, laboratory testing, leachate collection pipes.