The effect of sudden critical and supercritical hydraulic loads on backward erosion piping: small-scale experiments

Abstract

Backward erosion piping is an important failure mechanism for cohesive water-retaining structures which are founded on a sandy aquifer. This paper studies the effect of the sudden application of critical and supercritical hydraulic loads in small-scale experiments. For supercritical loads, it is clear that a part of the upper sand bed goes in suspension before being eroded, resulting in a relatively dense sand–water mixture being transported through the eroded pipe. A linear relation is found between the average velocity at which the pipe grows from downstream to upstream and the applied supercritical load. The pipe cross section is measured at the end of each test. The variations in pipe width, depth and cross section give more insight into the hydraulic regime within the pipe. The clear correspondence for gradual loading and sudden critical loading, and a smooth transition to higher supercritical loads, indicates that the fundamental erosion mechanism may be the same. Finally, grain size analysis of the eroded sand shows that the finer portion of the sand is eroded in case of subcritical or critical loading, while the coarse grains are eroded in case of supercritical loads.