Unsaturated slope stability around the Three Gorges Reservoir under various combinations of rainfall and water level fluctuation

Abstract

As sudden catastrophic geological disasters, landslides always cause numerous casualties and much property damage. Landslides in reservoir areas are rarely caused by a single influential factor such as rainfall or fluctuation of reservoir water level (FRWL); rather, they are frequently caused by the combination of influential factors. Since rainfall and FRWL conditions vary by location in reservoir areas, it is necessary to discuss slope stability under various possible combinations of rainfall and FRWL while considering the specific characteristics of the region. In this paper, model tests on the slope stability of the Three Gorges Reservoir (TGR) area were conducted with S1 sand under three different rainfall and FRWL combinations. Additionally, numerical simulations on the model tests, in which an unsaturated soil constitutive model was selected to describe the mechanical–hydraulic behaviour of saturated/unsaturated soil, were conducted. In the simulation, to reflect the regional characteristics, a relationship between the rainfall infiltration rate and the unsaturated permeability of the sand was proposed. By carefully determining the parameters involved in the constitutive model, soil–water–air coupling finite element analyses were conducted to simulate the model tests on slope stability. By comparing the calculated results with the test results, the numerical method used in this paper offers satisfactory accuracy to describe the various failure mechanisms of the model slopes under different loading combinations. The results of both the model tests and the numerical simulation indicate that in the TGR area during one year of operation, a decrease in the reservoir water level combined with a long weak rainfall is more likely to trigger a landslide than the other combinations studied. Additionally, the combination of a short heavy rainfall with FRWL in the short term during the wet season can be dangerous; thus, this combination needs to be considered in the operation of the TGR.