Experimental investigation of interfacial erosion on culvert-soil interface in earth dams

Abstract

The erosion of soil particles within a dam, by water that seeps through the dam, is one of the most common causes of failure in levees and earth dams. This phenomenon can be more complex and dangerous when interacting with internally affiliated structures, such as water-supply culverts, due to the potential development of seepage channels through the weak interfaces. However, the erosion in this particular case has not been thoroughly investigated. In this paper, therefore, a seepage apparatus is designed to simulate and investigate the progressive failure mechanism of interfacial erosion on the culvert-soil interface of earth dams. This further leads to a detailed investigation of the threshold and failure hydraulic gradients of interfacial erosion by accounting for the influence of two critical geotechnical factors, i.e., the degree of compaction and the clay content. Furthermore, numerical analyses are carried out to reproduce the seepage-induced interface stress-displacement behaviour, as a supplement to the experimental investigations. Finally, emphasis is placed on studying the protective effects of two typical mitigation measures (the filter layer and impermeable rings) against interfacial erosion. The main conclusions can be drawn as follows: (1) The interfacial erosion in the unprotected cases shows a three-stage progressive failure as the hydraulic gradient increases, i.e., the stable, transition and failure stages, while that of the protected cases shows a four-stage failure, i.e., the stable, transition, hardening and failure stages. (2) The threshold and failure hydraulic gradients of interfacial erosion are found to be in the ranges of 0.771–1.467 and 0.974–1.994, respectively, for the investigated cases. (3) The critical hydraulic gradients are seen to be in a nonlinear relation with the degree of compaction or the clay content. (4) The experimental results show the effective protective effects of employing the two mitigation measures against interfacial erosion by blocking the formed seepage channels. The research provides critical references for the safety assessment of embankment dams when considering interfacial erosion failures at culvert-soil interfaces.