以尤拉-拉格朗日耦合分析進行同震山崩之數值模擬：以熊本阿蘇大橋為例

坡地塊體崩塌為常見的地質災害之一，而引發崩塌的因素眾多，如降雨事件、地震事件，以及人為開發等。其中，當規模較大的地震發生時常會誘發邊坡的崩塌，並且常因不了解同震崩塌的動力過程以及運移狀況，在崩塌發生時往往會造成嚴重的災害。近年來透過數值方法對崩塌進行模擬逐漸成為有力的研究工具，而有限元素分析(Finite element analysis, FEA)則是常用的數值模擬方法之一，本研究將以有限元素法之模擬軟體Abaqus進行三維的坡地塊體崩塌之模擬。由於崩塌作用屬於坡地塊體劇烈變位的現象，而傳統拉格朗日分析法在元素大量變形時，網格會過於扭曲使得模擬無法正常計算。因此本研究採用尤拉-拉格朗日耦合分析(The Coupled Eulerian-Lagrangian analysis, CEL)，克服在拉格朗日分析中無法處理元素過度扭曲的問題，以模擬崩塌時塊體劇烈變形及位移的現象。本研究以2016年日本熊本地震(MW7.0)誘發的阿蘇大橋崩塌為例，成功利用尤拉-拉格朗日耦合分析模擬崩塌塊體的滑移過程以及塊體的堆積分布。模擬結果顯示當熊本地震開始後約5 s至7 s時，位於邊坡源頭區的塊體從變形現象轉變為快速滑移行為，且滑移的速度最快可達到30 m/s。當塊體在邊坡上快速向下滑移時，將會侵蝕路徑上的表層材料，並將其鏟刮至下方邊坡以及河道處堆積。藉由計算出崩塌塊體作用於邊坡上的力與時間序列，可進一步瞭解塊體在滑移過程中加速或減速的現象。於本研究的結果中可以觀察到塊體在滑移過程中有3次減速的階段，並對應到地形的變化，可以了解地形的變化影響了塊體的運動速度。根據Newmark塊體滑動理論，配合模擬結果顯示當地表加速度超過0.15 g時，將會使邊坡上不穩定的塊體產生永久性位移，當累積永久位移量達5 cm至10 cm時，塊體將會從變形現象轉變為快速位移的行為。本研究結果顯示，利用尤拉-拉格朗日耦合分析對於崩塌作用進行模擬，可以有效地了解崩塌的發生條件以及運動狀態，將有利於未來對於坡地災害的研究與防災準備。

關鍵字

同震崩塌；有限元素分析；尤拉-拉格朗日耦合分析；阿蘇大橋崩塌

並列摘要

The landslide is one of the frequent geohazards, and many factors can cause it, such as massive rainfall events, earthquakes, and human activities. When large earthquakes occur, the coseismic landslides often appear around the mountain areas. Because of the lack of understanding of the dynamic processes of coseismic landslides, the landslides may cause catastrophic disasters. In recent years, numerical simulation of landslides has become a powerful tool, and the finite element analysis (FEA) is also one of the commonly used numerical methods. Since the landslide process involves large deformation , the traditional Lagrangian analysis will be limited by the extreme mesh distortion. For this reason, the study adepts the Coupled Eulerian-Lagrangian analysis (CEL) to simulate the sliding process of blocks. This study successfully simulates the sliding process of the block and deposit area of the Aso-Bridge landslide induced by the 2016 Kumamoto earthquake. According to the simulation results, when the ground acceleration exceeds 0.15 g, the block in the source area of the slope transfers from deformation to rapid slip behavior, and the maximum sliding velocity can reach 30 m/s. By calculating the force and time series during the movement of the collapsing block, the acceleration or deceleration during the sliding process can be exhibited. It can be observed that the block decelerates three times during the sliding process, which corresponds to the change in terrain. Using the CEL method to simulate the landslide can effectively comprehend the dynamic sliding process, which be beneficial to future research of slope disasters.

並列關鍵字

coseismic landslide ； finite element analysis ； Coupled Eulerian-Lagrangian analysis ； Aso-bridge landslide

參考文獻

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Bhattacharya, S., Hyodo, M., Nikitas, G., Ismael, B., Suzuki, H., Lombardi, D., . . . Goda, K. (2018). Geotechnical and infrastructural damage due to the 2016 Kumamoto earthquake sequence. Soil Dynamics and Earthquake Engineering, 104, 390-394. doi:10.1016/j.soildyn.2017.11.009

Chang, K.-T., Chiang, S.-H., & Hsu, M.-L. (2007). Modeling typhoon- and earthquake-induced landslides in a mountainous watershed using logistic regression. Geomorphology, 89(3-4), 335-347. doi:10.1016/j.geomorph.2006.12.011

Chen, Y., Zhao, W., Han, J., & Jia, P. (2019). A CEL study of bearing capacity and failure mechanism of strip footing resting on c-φ soils. Computers and Geotechnics, 111, 126-136. doi:10.1016/j.compgeo.2019.03.015

Dai, Z., Huang, Y., Cheng, H., & Xu, Q. (2016). SPH model for fluid–structure interaction and its application to debris flow impact estimation. Landslides, 14(3), 917-928. doi:10.1007/s10346-016-0777-4

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以尤拉-拉格朗日耦合分析進行同震山崩之數值模擬：以熊本阿蘇大橋為例

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