Combined Effect of Rainfall Seepage and Seismic Shaking on Slope Stability by Using a Three-Dimensional Stability Analysis

Abstract

Taiwan is located in the Pacific Rim seismic zone and has a subtropical climate and mountainous areas. As a limited amount of area in Taiwan can be categorized as plains, the mountainous areas are used for development requirements. Overdevelopment on weak slope lands causes them to collapse and further exposes the lands to natural disasters such as earthquakes and torrential rains. Thus, appropriate slope stability analysis methods and engineering design measures should be proposed for slope lands. The purpose of this study was to discuss the combined effect of seismic shaking and soil seepage due to rainfall on slope lands by analyzing their combined effect on the factor of safety (FS) and failure mode of a slope land. A slope stability analysis was conducted using finite difference analysis, performed with FLAC3D. The soil strength reduction method was adopted to identify the FS of slopes in a static state by using FLAC3D. The formation of plastic sliding zones as the ratio of soil strength reduction was defined as FS in the seismic analysis. This study employed earthquake time history data of the Chi-Chi earthquake recorded at the Shihgang Dam station in the central region of Taiwan. The combined effect of seismic shaking and soil seepage due to rainfall was analyzed to determine its influence on the FS of the slope. The proposed method, which analyzes the combined effect of seismic shaking and rainfall seepage on the FS, obtains superior results to the conventional method, which analyzes the effects of seismic shaking and rainfall seepage separately.