Effect of Fine Particles and Soil Heterogeneity on the Initiation of Suffusion

Abstract

Hydraulic backfill structures can be affected by internal erosion, which develops if 2 conditions are met: detachment and migration of particles due to hydraulic seepage. Suffusible soils involve an easy movement of fine particles within the matrix, and this process depends on the particle size distribution of the soil and hydraulic load. If suffusion in homogeneous soils has been widely studied, it has rarely been approached in heterogeneous soils. Cohesionless soils can involve many heterogeneities, due to gap grading or segregation, which can be a cause of internal erosion under severe seepage. In this study, attempts are made to evaluate the influence of fine particles type, rate and distribution of heterogeneity on the onset and development of suffusion. This process is investigated by using a soil sample within a column, submitted to a horizontal unidirectional flow. Different types of fines (kaolinite, illite, silt) and three configurations (central, downstream, and distributed) involving different rates are used by the introduction of coarse sand into a mixture of fine sand and fine particles. Two heterogeneity rates of 20% (weak heterogeneity) and 60% (high heterogeneity) were used and the results were matched with those obtained on the homogeneous soil. The results show that among the fine particles tested with the same configuration and heterogeneity rate, illite provides the highest resistance to suffusion. In addition, suffusion increases with the heterogeneity rate above a given threshold value. These results help us to assess a better understanding of the effect of heterogeneities on the transport and retention mechanisms of fines in granular soils.