Investigation of the backward erosion mechanism in small scale experiments

Abstract

Currently, the most advanced prediction model for backward erosion piping is the two-dimensional Sellmeijer model that relates the equilibrium of forces on the grains at the pipe bottom to the pipe flow and ground water flow, based on mainly theoretical formulae. Yet the suitability of theoretical formulae for pipe flow and erosion under these specific conditions has not been verified experimentally. To understand and validate the erosion mechanism at micro-scale and to model the hydraulic conditions in and around the pipe in a 3D situation, the characteristics of the pipes and the erosion in the pipes have been investigated in small-scale laboratory experiments. The experiments indicate that the pipe depth and the pipe gradient remain the same during lengthening. The results serve as input for 3D groundwater flow calculations to obtain a better understanding of the erosion mechanism. The combined numerical and experimental results indicate that it is likely that the erosion at the pipe tip is triggered by loosening of sand from the pipe tip and walls as a result of water inflow rather than scour at the pipe bottom.