Assessment of internal stability of sand–fine mixture using particle detachment model and its implications on suffusion

Abstract

This study investigated the microscale assessment of the stability of fine particles from calculated hydrodynamic and adhesive torques of attached fine particles on sand particles. Higher hydrodynamic torque applied to the attached fine particles than the adhesive torque was regarded as the detachment of fine particles (unstable condition). A triangular chart and surface plot were used to illustrate the stability of fine particles from the calculated hydrodynamic and adhesive torques at a wide range of size ratios, ionic concentration, and Darcy’s velocity. In addition, the randomly sampled radius of sand and fine was applied to the model to assess the probability distribution of the ratio between hydrodynamic and adhesive torque as a function of ionic concentration and flow rate. The obtained triangular charts for illustrating the stability of fine particles indicated that the fine particles are stable at relatively high ionic concentrations and low size ratios. Furthermore, the probability of unstable conditions decreases as the standard deviation of the particle size distribution of fine increases for relatively high median size, while the reverse trend was observed for relatively low median size. In addition, the initiation of suffusion observed from soil-column experiments correspond to unstable zone implies the need of considering reattachment and the link between the microscale detachment model to the macroscale parameters to incorporate the detachment model for simulating suffusion.