Experimental Study of Suffusion in Sand-Clay Mixtures under Variably Saturated Conditions

Abstract

Suffusion refers to the loss of small particles in a soil matrix without volume changes, caused by hydrodynamic forces and alternation of pore fluid chemistry. This study investigated the ionic concentration (IC)-induced suffusion of sand-clay mixtures under saturated and unsaturated conditions through laboratory soil-column experiments. The impacts of clay mineralogy and sand-grain size on suffusion were investigated based on the breakthrough curves (BTCs) obtained from the soil-column experiments. In addition, the degree of saturation during the experiments was measured to assess the impact of the saturation state on suffusion in the sand-clay mixtures. The observed BTCs in this study demonstrated that suffusion was more significant under saturated conditions than unsaturated conditions for the sand-kaolinite and sand-illite mixtures. In contrast, the sand-bentonite mixtures exhibited higher susceptibility to suffusion under unsaturated conditions. Moreover, for the sand-kaolinite mixtures, a higher susceptibility to suffusion was observed with smaller sand-grain sizes under saturated conditions, whereas the opposite trend was observed under unsaturated conditions. This study provides insights into the suffusion behavior of sand-clay mixtures, considering influential factors such as clay type, sand-grain size, and IC gradient under both saturated and unsaturated conditions, which highlight the importance of considering the saturation state for a comprehensive understanding of suffusion in the sand-clay mixtures.