Soil hydro-mechanical behaviors subjected to large and cyclic hydraulic loadings under anisotropic stresses

Internal erosion, which involves the detachment and migration of soil particles from the soil matrix driven by seepage flow, occurs frequently in natural slopes, dikes and many other geotechnical and hydraulic structures. Previous studies primarily focused on soil internal erosion under the isotropic stress state and monotonic hydraulic loadings. However, the soil in engineering practices is under more complicated hydro-mechanical conditions, i.e. anisotropic stress states, and subjected to large and cyclically unsteady hydraulic loadings due to water level fluctuations. Under such conditions, the soil internal erosion process differs significantly from that under the monotonic seepage and isotropic stress states. Therefore, in this study, extensive laboratory tests were carried out to investigate the soil hydro-mechanical behavior subject to high cyclic hydraulic gradients and various stress states. Results show that the soil experienced a gradual internal erosion process under an isotropic or low shear stress state, whereas it experienced rapid erosion followed by a complete failure when the stress ratio (η) was high. The cyclic hydrodynamic loading accelerated the occurrence of internal erosion due to strong disturbances to the soil structure. The soil pores became continuously connected under high cyclic hydraulic gradients, leading to significant soil deformations due to the collapse of soil force chains by massive particle loss. Additionally, the peak and critical friction angles for all the post-erosion soils decreased considerably and the soil tended to exhibit strain softening behavior after erosion at large cyclic hydraulic gradients.