Three-Dimensional Stability of Slopes under Water Drawdown Conditions

In practical engineering, slopes near reservoirs are susceptible to collapse during the rising and falling of water levels, resulting in huge financial losses. Three-dimensional (3D) upper-bound analysis is an effective vehicle to assess slope stability under water drawdown. However, in previously published 3D upper-bound analysis, the pore water pressure distribution caused by drawdown is often approximately determined by employing a pore-pressure coefficient, which is not theoretically sound and fails to give rigorous upper-bound estimations of slope stability. To overcome this shortcoming, the hydraulic head distribution of a slope subjected to drawdown was determined numerically using seepage flow calculations. The obtained hydraulic head distribution was subsequently incorporated into the 3D rotational failure mechanism of the kinematic approach of limit analysis, so as to deliver an upper-bound solution to slope safety factors. To validate the proposed approach, a case study on the Chenjiawan slope at the Three Gorges Reservoir, China, and comparisons with numerical calculations and previous studies are performed. Four different drawdown conditions are considered in this study and corresponding stability charts are provided for directly assessing the safety factors of slopes subjected to different drawdown conditions. The effects of different drawdown processes on the slope’s stability are studied, showing the unfavorable effect of the external drawdown process and the beneficial effect of the internal drawdown process.