| Summary: | 碩士 === 國立成功大學 === 資源工程學系碩博士班 === 97 === There are a lot of landslides happened in Taiwan during rainy seasons. A correlation between rainfall and slope stability has been studied. There has been much research conducted on the effects of rainfall on unsaturated soil slopes. The one of mechanisms that leads to slope failures is the pore water pressures starting to increase when water starts to infiltrate the unsaturated soil zone. The failures have been attributed to the advancement of a wetting front into slopes until it reaches a depth where it triggers failure. Conventional methods for slopes stability analysis, assuming fully saturated (or dry) behaviors on slope, cannot be described successfully under unsaturated conditions.
In this study, the finite element computer program SEEP/W is used to simulate the changes in pore water pressure when the slope is subjected to different rainfall events. Finally, the pore water pressure distribution computed in the program SEEP/W is imported into SLOPE/W for the slope stability analysis. The time-dependent pore water pressure distribution could therefore be used to compute the factor of safety with time directly.
This thesis is divided into two parts, the first part is to process sensitivity analysis of controlling parameters, including general geometry, soil property, rainfall intensity and rainfall pattern. This results indicate soil property and rainfall intensity are the most important factors to influence slope stability.
In the second part, the Songmao region in Taichung, Taiwan which has been examined by modeling local rainfall events and coupled with the monitored data from field to determine the slope stability mechanism. By the rainfall events, the simulation indicated safety factor of slope decreased by less than 1.0 when the rainfall infiltrates at 2.0m depth and the monitored data also revealed displacement in the evidence. In conclusion, the slope failures have been attributed to the increase of pore water pressure and decrease of shear strength when rainfall triggers failure. Therefore, the main reason to make Songmao region slope instability is rainfall infiltration.
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