Two-dimensional finite element modeling of seepage-erosion coupled process within unsaturated soil slopes

Fines migration along with rainfall infiltration is a possible cause of failures of slopes composed of loose deposits. To investigate the intrinsic mechanisms, a rigid mathematical model which can fully capture the multi-phasic and multi-physical process is necessary. In this research, the macro and micro physical phenomena of fines migration process within deposited soil slopes under rainfall infiltration were summarized. Based on the mixture theory, a seepage-erosion model for unsaturated erodible soils capable to capture these phenomena mathematically was built based on a rigid theoretical framework. The model was used to simulate a set of rainfall flume tests involving fines migration phenomena with the finite element method. Two distinct slope failure modes observed experimentally, which were induced by the soil erosion-deposition properties, can be well reproduced by our numerical model. The seepage-erosion coupled process during the rainfall infiltration, as well as the intrinsic mechanism responsible for the slope failures, was illustrated in detail based on the numerical results. It was shown that the fines migration process can affect the hydro-mechanical response within unsaturated slopes significantly, and therefore special attention should be paid to those soil slopes susceptible to internal erosion.