Experimental and Numerical Investigation of Internal Erosion Effect on Shear Strength of Sandy Soils

Abstract

Internal erosion is a complex process which is considered as the main cause of hydraulic works failure. It involves detachment and transportation of fine particles from the soil matrix, due to seepage flow. The susceptibility of dikes and dams to internal erosion has been widely investigated. However, its effect on soil shear resistance characteristics was less reported. This study presents an experimental and numerical investigation of internal erosion effect on the shear strength of sandy soils. In the first step, direct shear tests without erosion were carried out on sandy soils made of sand mixed with three types of fine particles at different contents (10%, 15%, 20%). In the second step, sequential erosion-shear tests were conducted using a modified shear box that permits seepage through compacted specimens and allows collection of effluent with eroded particles for further evaluation of the effect of extended internal erosion on soil shear strength. The results showed that the finer the mixture, the more its cohesion is altered by erosion. So, after erosion, both cohesion and internal friction angle decreased for the different fines contents tested. A numerical model based on porosity diffusion law was used to simulate the soil strength alteration due to suffusion, and comparison between experimental and numerical results indicated a quite good agreement for cohesion reduction. Sequential erosion-shear tests carried out on different mixtures have shown that internal erosion affects shear strength characteristics and can lead to the instability of soil slopes, dikes, dams and flood protections.