Effect of suffusion and self-filtration on mechanical behavior of well-graded sands

Suffusion in well-graded sands is a significant concern in geotechnical engineering, potentially leading to malfunctions or failures in soil slopes, earth dams, and their foundations. In this paper, two internally unstable well-graded sands of various densities are subjected to seepage tests and consolidated undrained triaxial compression tests using an in-house developed triaxial permeameter. The tests explore the impact of the uniformity coefficient (C_u), initial density, and hydraulic loading amplitude on suffusion. The effect of suffusion on the undrained mechanical behavior is investigated. The results indicate that specimens with smaller C_u and higher density exhibit a larger onset hydraulic gradient for suffusion, resulting in a smaller eroded mass and fewer changes in permeability. Increasing the hydraulic loading amplitude leads to a larger eroded mass and more changes in permeability. Compared to non-eroded specimens, eroded specimens exhibit reduced shear strength and stiffness during compression tests, increased strain-softening, and contractive behavior. A post-test particle-size distribution analysis shows a significant increase in particles smaller than 0.425 mm within the eroded specimens’ midsection, in contrast to a reduction in the top section. This leads to clogging in the midsection, due to seepage, and a non-uniform particle-size distribution throughout the specimens. Suffusion also causes a decrease in mean effective stress at the critical state in the specific volume-mean effective stress plane.