Erosion process of a core clay in earth and rockfill dams : laboratory experiments and numerical modelling

Abstract

Internal erosion of dam’s embankments is a complex process and considered as the main cause of hydraulic works failure. Laboratory experiments provide a potential insight into the processes involved. Particles detachment from a core of earth and rock fill dams within a crack submitted to water seepage may lead to backward erosion which gradually progresses till forming a pipe. Clay of designed core must provide a quite good resistance against erosion, which depends on material and flow characteristics. The present study reports the results from hole erosion tests (HET) aiming to assess the erodibility of a clayey soil collected from a deposit by Tipaza (Algeria) and used in the core confection of an earthen dam. For this purpose, tests were performed under successive hydraulic loads and the pressure drop was measured as close as possible to the pipe edges. Hydrodynamic parameters effect on erosion rate of tested soil was investigated and the susceptibility of tested soil to erosion was addressed. A numerical simulation of turbulent flow in hole pipe using FEM was carried out to approach the hydrodynamic process occurring inside the hole and to compute shear stress acting along the wall. Numerical values of local shear stress were matched with analytical values and used to describe the area impacted by erosion and the hole radius evolve. Numerical results showed that the usual analytical evaluation of shear stress along the hole overestimates strongly the effect of seepage on the hole wall. Attempts are also made to assess the erodibility classification of tested soil from analytical and numerical results to estimate the deviation usually affecting the interpretation of HET