Landslides and slope failures cause an annual loss of billions of dollars of properties and death of thousands of people. In the past few years, the loss due to landslides mainly after pre and post-earthquake rainfall events increased significantly. In this study, a systematic analysis was performed on the effect of rainfall after the slope is shaken by different scales of cyclic motions and vice versa. Soil samples collected from a landslide site at a compacted fill location in Southern California and were compacted separately at different void ratios and angles of inclinations. The slopes were instrumented with numerous accelerometers, tensiometers, and inclinometers. The slopes were first subjected to cyclic motions at different magnitudes and frequencies and post-shaking spatial deformations were measured. Then the slopes were subjected to different magnitudes of rainfalls until they got saturated and pore spatial distribution of wetting front, pore pressure, and deformation were measured with time. Likewise, the slopes were first subjected to rainfall and same cyclic motions were applied after the rainfall event. Deformation, pore pressure, and movement of wetting fronts were measured to compare the effects of each triggering factors on slope stability. The result shows that both pre and post earthquake rainfall effect dramatically increase slope deformation and reduce the factor of safety of the slopes.
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