板岩邊坡在極端降雨下之邊坡穩定分析

Slope stability analysis under extreme rainfall in slate slope

劉冠麟(Kuan-Lin Liu) ； 盧之偉(Chih-Wei Lu) ； 林宏明(Hung-Ming Lin)

《中華防災學刊》 11卷1期 (2019/03) Pp. 19-32

摘要

隨著全球暖化與氣候變遷影響，極端降雨事件未來可能成為常態，重大災害將更加頻繁。每逢颱風、豪雨等降雨季節期間，對於極端降雨常會誘發較嚴重之深層崩塌坡地災害。分析近二十年來臺灣各地區致災性豪雨降雨資料，發現邊坡災害之成因多是「連續降雨過多」或「短延時雨量過強」所致。以輕度變質之板岩為例，其構成邊坡板岩材料抗侵蝕能力相較於泥岩或頁岩材料為高，惟板岩極易沿其葉理方向裂開，轉為細碎薄片狀之面狀構造，當板岩劈理受邊坡長時間重力及風化作用後，其材料將逐漸弱化而造成潛變（creep）行為，即板岩邊坡變形過程中，亦會發展節理裂隙，促使降雨入滲引致地下水位抬升岩屑崩滑可能性增加。為探討不同降雨強度引致地下水位抬升對邊坡穩定之影響，本研究以數值分析軟體SEEP／W模組模擬降雨引致地下水位抬升，再利用SLOPE／W模組探討已知滑動面之地下水位抬升與邊坡穩定之關係，以深層崩塌高風險區之臺中市梨山區松茂崩塌地為板岩邊坡區域進行模擬分析。為因應極端氣候造成降雨回歸周期的改變，本研究應用前峰型、中峰型、後峰型、平均型等設計雨型，對邊坡進行模擬分析，嘗試建立降雨引致邊坡壞預警系統。經模擬分析及驗證後提出降雨延時與累積降雨量之關係及最高地下水位累積降雨量與水位抬升高度之關係兩種模式，做為評估之基準。

關鍵字

深層崩塌 ； 極端降雨 ； 板岩 ； 累積降雨量

並列摘要

With global warming and climate change issues, extreme rainfall events in the future may become the normal, causing severe disaster events will be more frequent. During the rainy season such as typhoon and heavy rain, severe rainfall often induces more serious slope disasters. Analysis of the devastating heavy rainfall in Taiwan in the past two decades, the occurrence of slope disasters is mostly caused by ＂excessive continuous rainfall＂ or ＂short-duration rainfall＂. For mild metamorphic slate, its erosion resistance is higher than that of mud or shale. However, the slate is easily split along its cleavage direction and turned into a finely-cut sheet. When subjected to long-term gravity and weathering, the material of shale will gradually become weaken and turn into creep. That is, during the deformation process of slate slope, joint fissures will gradually grow out. When the rainfall infiltration leads to groundwater level rise, the possibility of rock debris collapse will increase. In this study, high- risk areas with deep collapse were selected for analysis, taking Songmao Landslide area in Lishan District as examples. To simulate groundwater level rise caused by rainfall, this study conducted SEEP/W module of GeoStudio numerical software. The groundwater level monitoring data will be used for verification. Then, the SLOPE/W module of GeoStudio numerical software is used for slope stability analysis. Exploring the relationship between groundwater level rise and safety factor of slope is one of the main task in this study. The uncertainty of rainfall caused by extreme weather is researched herein. In this study, the design of rainfall patterns such as advanced, intermediated, delayed and uniform rainfalls models were simulated. This study tried to establish a deep- seated landslide disaster warning system. After simulation analysis and verification, the relationship between rainfall duration and accumulated rainfall and the relationship between the maximum groundwater level cumulative rainfall and water level elevation were proposed as the evaluation criteria.

並列關鍵字

Deep-seated landslide ； Extreme rainfall ； Slate ； Cumulative rainfall