3D stability of partially saturated soil slopes after rapid drawdown by a new layer-wise summation method

Classical approaches for evaluating the stability of soil slopes or dams after rapid drawdown were mostly performed under fully dry and/or saturated conditions. The suction-induced effect of unsaturated zone was generally neglected in assessing the slope stability after rapid drawdown. This paper develops a novel three-dimensional (3D) limit analysis method to evaluate the stability of a partially saturated soil slope in the pore-water drainage process. A framework is formulated based on the 3D rotational failure mechanism by taking the effects of suction and the effective unit weight of unsaturated zone into account. A layer-wise summation method (LSM) is developed to calculate the work rate of unsaturated soil weight and the internal energy dissipation rate. Extensive parametric studies are performed to explore the effects of suction, strength parameters and hysteresis on the slope stability. Examples are also given to demonstrate the 3D effect on the slope stability. The stability will be underestimated when the suction is not considered in the slope stability analysis. The suction-induced effect enhances in the pore-water drainage process and reaches the maximum when the pore-water is completely drained.