地震引致邊坡崩塌之影響範圍與滑動量數值模擬

Abstract

邊坡崩塌往往容易造成人員及財產的損失，921集集大地震後台灣山區的崩塌災害規模與數量甚大，相關減災工程規畫都需要調查災害的規模與崩塌量體才能進行評估。對於歷史災害的調查多藉由航照與衛星影像進行崩塌圈繪與統計，但對現地災害情況往往不夠了解，只藉由航照與衛星影像無法區分各事件崩塌區與堆積區，因此若能模擬預測崩塌事件的影響範圍，即可針對預測範圍地區進行人員疏散、邊坡整治或整體規劃，因此模擬邊坡崩塌影響範圍對於防災有極大的參考價值並影響工程規畫的經濟效益。 本研究建立一套適合應用於邊坡受震的數值模擬模式，以模擬邊坡受震崩塌的滑移量與影響範圍。首先以小型振動台試驗之結果進行模擬及驗證，數值模擬動態分析過程中，假設剪應力最大的時間點為主要滑動面發生時間，以此剪應變分佈區界定滑動面。第二部分建立滑動模型，對滑動面設定介面性質，滑動面以上的土壤因受力而變形、下滑，最後能量消散而停止滑動。將模擬結果與前人實驗結果進行比對，當界面摩擦折減係數為0.85時，模擬結果之崩塌塊體滑移距離與崩塌影響範圍之比值，與試驗結果非常相似。 進一步應用數值模擬崩塌滑動模式在實際案例上，以南投縣眉溪流域內崩塌實例進行數值分析模擬，探討案例邊坡受921集集大地震之影響，建立滑動模型進行動態分析，並根據崩塌案例之數值模擬結果，統計出崩塌影響範圍之2/3長為崩塌塊體水平向長度，崩塌影響範圍之1/3長為崩塌滑移距離；航照判識取得崩塌影響範圍之水平距離，可以線性公式計算崩塌下緣與上緣水平滑動距離。崩塌上緣與下緣滑動水平距離也大致呈線性關係。

Landslides often cause deaths, and the loss of properties. The damages caused by 921 Chi-Chi earthquakes in Taiwan are tremendous, and are needed detailed investigation to access the affected area of landslides for mitigation measures. Study of landslide disasters had been conducted by the satellite images and aerial photos. However, the engineering projects often required assessment from the on-site data. To provide information for landslide hazard mitigation, the numerical simulation can offer a more reliable and assessment of affected area and run-out distance. A numerical model for simulation of earthquake-induced landslide to simulate the landslide affected area is developed in this study. The first step of simulation is to verify the small shaking table experiment. The maximum shear stress occurrence time is defined as the sliding surface forming period, and the sliding surface was determined with the graphic of maximum shear strain increment. The second step is developing the sliding model and input parameters of sliding surface. The material on the sliding surface deforms, then slides along the interface, and stops when energy deplete. We compare the results of numerical simulation with the experiment to discuss the correlation between affected area and run-out distance. The numerical model for simulation of landslide behavior was applied to real landslide cases in May River Basin, Nantou County. We developed the dynamic sliding model of each case for studying the influence of 921 Chi-Chi earthquakes, and discussions on the correlation between affected area and run-out distance with the analyzing result of case study were conducted. The statistics consequence from simulation results show that 2/3 of the horizontal length of the affected area is about the length of landslide block, and 1/3 of the horizontal length of the affected area is about the length of run-out distance. Furthermore, if the affected area could be determined with satellite images and aerial photos, the run-out distance can be calculated from the linear formula in this study.