Effect of soil erosion on filters behavior in hydraulic structures

Cohesive soils with a large amount of fine particles are usually found in embankment dams. In order to prevent erosion of base soil and simultaneously to allow seepage, filters are designed and managed downstream of these structures. The filters grading is mainly designed using filter criteria [Sherard, Dunnigan 1985], which are based on relationships between the particle size (d(85)) and the opening size of the filter (D-15). This paper reports experimental results obtained on the soil-filter system behaviour subjected to different hydraulic and geometrical conditions. The particles' transport and filtration of two clay soils through a granular filter are investigated. The importance of the effect of successive filtration on the porosity reduction under a constant load is evaluated. A comparison of the porosity and permeability reduction revealed extend of fine particles detachment and deposition during erosion process. Moreover, important results are developed for predicting a capacity of fine particles retention in filter's pores.