Hirofumi IKEMOTO

Slope Stability Analysis for Rainstorm Taking Account of Unsaturation-saturation Seepage Flow

Satoru OHTSUKA


Slope failure due to rainfall is mostly a surface failure of weathered layer. The weathered soil is usually unsaturated and the cohesion is greater than the case of saturation. With the increase in saturation, the cohesion of soil decreases and the generation of pore water pressure with complete saturation decreases the effective stress of soil. The slope stability varies in time as seepage proceeds with rainfall. This study aims to simulate the slope stability in time due to rainfall. Three dimensional slope stability analysis combining an unsaturation-saturation seepage analysis and a stability analysis of rigid plastic FEM was developed. The following conclusions were obtained.
1) Strength reduction type rigid plastic constitutive equation was newly developed with Penalty formulation for slope stability. The applicability of rigid plastic FEM to slope stability was examined.
2) Movement of free water surface due to rainfall causes the change in flux condition. This behavior was well simulated with newly developed algorithm in computation. Flux due to rainfall was also controlled in consideration with seepage property of slope.
3) Slope stability for rainstorm was well estimated. The effect of rainstorm and seepage properties on slope stability was examined. It was found that slopes mostly failed with complete saturation.