Modelling of flow in backward erosion pipes

Abstract

Backward erosion piping is an important failure mechanism that can affect the safety of water-retaining structure foundations, which results in the formation of shallow pipes at the interface of the cohesive layer and the sand layer. Pipe hydraulics provides a lot of valuable information about the erosion mechanism, but it had never been analysed systematically during equilibrium. This paper analyzes pipe hydraulics by combining the pipe flow model and numerical simulations of experiments. A single-phase pipe-flow model is presented that includes not only frictional and accelerational pressure drops, but also the pressure drop caused by inflow through the pipe wall. The pipe-flow model is included in pipe/aquifer coupling numerical models to achieve more accurate predictions of pressure drop and inflow distribution along the pipe. The predictions agree favourably with previously published experimental data. And the calculated pipe flow velocities, hydraulic regimes and gradients are analysed for different pipe lengths.