台灣每遭逢颱風事件或是在春夏交接之梅雨季節，常有邊坡滑移或破壞事件發生，而在非雨季邊坡滑動災害較少發生，因此可推知降雨與邊坡滑動間有ㄧ定之關係。在許多研究中已經提出降雨事件會對淺層邊坡造成某一程度影響，主要是由於未飽和層中潤濕帶隨降雨入滲所增加至一定的臨界深度，導致未飽和層中原有的孔隙水壓增加而進一步使得剪力強度下降，導致坡地發生滑動破壞，而在傳統探討邊坡發生不穩定的問題大都將土體視為完全乾燥或完全飽和以分析其穩定性，其不能充分表現出實際邊坡的未飽和狀態。

本研究主要利用二維有限元素滲流分析來模擬未飽和層中之降雨入滲行為，其邊坡穩定分析中結合滲流理論，探討降雨入滲在未飽合淺層邊坡中孔隙水壓之改變對坡地穩定的影響，本研究利用數值分析軟體Geo-Studio模擬雨水入滲至未飽和邊坡之行為，以SEEP/W進行邊坡滲流分析，將所得之壓力水頭資料輸入邊坡穩定分析軟體SLOPE/W求得各時間段安全係數之變化，進而探求降雨入滲造成淺層邊坡滑動之機制。

本論文主要分為兩部份，首先進行均質邊坡穩定影響因子敏感度分析，包含邊坡幾何、土壤材料性質、降雨強度及降雨類型，由結果顯示隨著坡角、坡高及降雨強度增加易造成邊坡不穩定，而土壤材料性質與降雨強度為最重要決定因子，其決定坡地因降雨產生的入滲條件，進而造成土壤中孔隙水壓的變化情況。

本研究以台中縣松茂地滑區為研究區域，以現地實際降雨事件為例進行模擬，結合現場鑽探資料比對驗證松茂地滑區之滑動機制。由降雨事件模擬結果顯示，松茂地滑區遭逢降雨時邊坡淺層土壤孔隙水壓力變化顯著，且當雨水入滲至約2m時，邊坡安全係數有明顯下降至臨界值1.0之趨勢，並由現地傾度管監測資料顯示有明顯位移現象，因此本研究以數值模擬之結果是符合松茂地滑區之滑動機制，可以作為未來對於松茂地滑區坡地穩定研究之參考。

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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