Erosion Experiments on Culverts and Sewers Using a New Test Facility

Leakage through joints in rigid sewers or corrosion-induced perforations in corrugated steel culverts can result in ingress of groundwater and erosion of the surrounding fill. The loss of ground support may then compromise the ability of the sewer or culvert to support earth or vehicle loads. A new test facility at Queen’s University has been developed to undertake erosion experiments to measure the impact of erosion on sewer and culvert behavior. Use of the 5 m long, 3 m wide, and 4.5 m deep test pit to investigate the response of large diameter pipes under deep burial has been described previously, and this paper describes its use for erosion experiments. This is illustrated by outlining a test conducted on a corrugated steel pipe with 0.9 m diameter and perforations along the haunches. This test pipe was instrumented with optical fiber sensors around crests and valleys of the corrugated plate. It was then placed in the pit and backfilled with sand. After initial burial, wheel pair loading on the ground surface was applied through a steel plate, and strains were measured around the pipe circumference. Those strains then were used to obtain the distributions of hoop thrust and circumferential bending moment for this “intact soil” condition. The test pit permits experiments in saturated ground, and after raising the level of the groundwater, leakage through the perforations commenced, causing erosion of the surrounding fill. After lowering the groundwater level to stop the erosion, surface loading was again applied, and the resulting strains measured for the steel culvert with this deteriorated (eroded soil) condition. Comparisons of the pre-erosion and post-erosion responses reveal that there are very significant changes in the patterns and magnitudes of circumferential bending moment, with a large bending moment developing where the soil support was removed by erosion.