Evolution of the Transient Saturated Zone and Stability Analysis of Slopes under Rainfall Conditions

To study slope stability and instability modes under rainfall conditions, an improved Bishop method is proposed according to saturated-unsaturated seepage flow theory. It can simultaneously consider the depth effect of rock and soil mass shear strength parameters, transient water pressure, groundwater pressure, saturated water softening, unsaturated strength, and pore water unit weight. The variation law of the transient saturated zone, potential slip surfaces and stability coefficient under rainfall conditions are analysed with this method. The results indicate that after rainfall starts, the transient saturated zone of the slope continuously expands, and the stability coefficient gradually decreases. After rainfall stops, the transient saturated zone of the slope dissipates rapidly, and the stability coefficient continues to increase. During the early rainfall period, the slope instability mode is deep-layer integral slippage. During the later rainfall period, the slope instability mode is shallow-layer local slippage. The depth effect and unsaturated strength are beneficial to the slope stability, while the transient water pressure, saturated water softening, and pore water unit weight are not. The application of this method in engineering practice is of great significance to slope stability analysis and protection under rainfall conditions.