Model Test on Backward Erosion Piping under a K0 Stress State

Piping is a major failure mechanism in both dams and dikes. In this work, we develop a transparent specimen tank that allows a camera to clearly record the piping formation process. In addition, this apparatus is able to maintain a constant hydraulic head and to apply K0 stress states. The eroded soil and the discharged water are measured using a collection system. We conduct a series of laboratory tests to investigate the evolution process and mechanisms of piping in gap-graded soils under a K0 stress state. Our results show that the piping process can be divided into three stages: seepage, pipe formation, and pipe wall erosion. No visible soil erosion and deformation is observed in the seepage stage. In the pipe formation stage, the flow channel is formed gradually from the position where water is injected into the exits. In the pipe wall erosion stage, grains are eroded mainly from the pipe wall. Moreover, erosion is more profound on the convex side than on the concave side of the pipe. From the sensitivity analysis, a large percentage of coarse grains can hinder the formation of the flow channel is observed. Finally, the transition mechanism from suffusion to piping based on different testing conditions is revealed.