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

The performance of a new laboratory facility for testing small-diameter bur ied 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 X 2.0 m l ong X 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 su ccessfully simulated with a pressurized air bladder. Boundary friction was limited to only minimal effects with lubricated polyethylene sheets. The st iffness of the lateral boundary is sufficiently large to induce lateral str esses close to those for zero lateral strain conditions. Overall, the effec ts on the pipe arising from the idealizations involved in the laboratory mo del were found to be small. The application of the new test cell is illustr ated by using it to assess the response of a small-diameter landfill leacha te 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 pip e deflections and strains were nearly twice as large when tested in the coa rse gravel compared with the sand backfill. Much greater variations of defl ection and strain were also measured with the coarse gravel when compared w ith the sand backfill due to local bending effects from the coarse gravel.