Internal Erosion of Clayey Soils Protected by Granular Filters

The process of internal erosion in an embankment dam with granular filters can be divided in five stages : (i) formation of the crack through the core, (ii) erosion of material from the crack walls due to the shear stress applied by flowing water, (iii) transport of eroded particles to the filter, (iv) retention or percolation of these particles within the filter, (v) continuation of erosion leading to piping failure, or sealing of the crack. The process is quite well known in case of non-cohesive base soils, but if the base is a clayey soil, the process is much more complex. Based on a large number of No Erosion Filter tests performed at the University of Granada, (Spain), this paper analyses the influence that have several base soil's variables in the internal erodability of clayey soils protected by granular filters, such as plasticity, mineralogy, water content, additives and hydraulic gradient.