Analysis of the pipe depth development in small-scale backward erosion piping experiments

Abstract

Backward erosion piping is an important failure mechanism for water-retaining structures. It results in the formation of shallow pipes at the interface of a sandy or silty foundation and a cohesive cover layer. This paper analyzes the depth of these erosion pipes through small-scale experiments. The development of the pipe depth reveals a lot of information on the backward erosion process, but it had never been measured systematically during the erosion process. Our analysis shows that the pipes are extremely shallow (in the order of mm) and that the pipe depth increases slightly, as piping progresses. Furthermore, a relation is found between pipe depth, grain size, soil permeability, and pipe length. The experimentally obtained depths are in good agreement with those obtained with theoretically determined pipe depths based on pipe hydraulics. Finally, the experiments are compared to 2D numerical simulations using Sellmeijer’s mathematical model and 3D numerical simulations with the correct pipe dimensions.