- 學位論文
物質點法分析邊坡崩塌過程與運動機制：以貓空邊坡為例
Material Point Method Analysis of Post-Failure Process and Kinematic Behavior of Landslides
摘要
山崩後土壤運移與堆積的範圍，以及是否會影響到下邊坡的保全對象，為防災與工程實務中所關切的重要議題，然而，針對邊坡災害的研究歷程，傳統極限平衡法僅能用於尋找滑動面與計算安全係數，有限元素法只適合用以模擬小變形的問題。有鑑於此，本研究選用物質點法分析邊坡破壞後之運動行為，如邊坡崩塌過程、山崩速度、土壤運移距離、堆積高度等。 本研究首先選用大型邊坡物理試驗進行數值模型驗證，確定數值分析模式的合理性，模型設定物質點為單相單點與雙相單點，並使用水力耦合進行分析，接著運用此模型進行一系列參數分析，以瞭解不同參數對邊坡破壞後的影響。研究結果說明，物質點法可以有效模擬邊坡崩塌後的行為，邊坡崩塌過程中剪裂帶發展也能精準掌握。除此之外，水力條件(如：土壤滲透係數、土壤飽和狀態)對於邊坡整體變形特徵最具影響力，隨著土壤滲透係數的增加或飽和程度的減少，可明顯有效降低邊坡變形的情形，而土壤凝聚力則能有效控制邊坡崩塌後的穩定。 進一步，本研究挑選台北市貓空兩處邊坡歷史災害進行分析與研究，兩處邊坡皆因2008年9月薔蜜颱風造成崩塌，且崩塌範圍皆涉及至重要保全對象。透過比對兩處邊坡崩塌後之實測地形剖面，發現物質點法能夠準確預測兩處邊坡的運移距離，惟土壤堆積受三維效應的影響，以二維的數值模式模擬會稍微高估山崩後土壤的堆積高度。邊坡崩塌過程中，土壤體積擠壓使孔隙水壓之激發，會加速邊坡的滑動速度，另外，下邊坡之土壤會受上方土體掩埋而堆積至最底部。然而，多組模擬結果顯示，運用不排水分析結果會較不吻合且偏向不安全分析。
並列摘要
There are two important issues of disaster prevention. One is the soil runout distance and deposit height and the other is the influence area of down-slope after landslide. According to the previous studies, the traditional limit equilibrium method focuses on the critical sliding surface and factor of safety. The finite element method is just suitable for simulating pre-failure behavior of landslides. Based on the statement above, this study used the material point method (MPM) to investigate post-failure behavior, including the kinematic behavior and failure process. The first stage of this research is to verify the proposed numerical model using the physical slope experiment result. The one phase-one point and two phase-one point are used in the numerical model. The fully coupled analysis is also chosen to observe the soil-water interaction. After that, a series of parametric studies to evaluate the influence of soil properties and slope conditions on the post-failure behavior of the slope. The analysis results indicate that the MPM successfully described the large deformation behavior. And it can accurately observe the development of the shear band. Additionally, the hydraulic conditions (i.e. soil permeability and the degree of saturation of soil) significantly influence the slope deformation characteristics. The cohesion of soil has effect on controlling the stability after the landslide. Finally, two landslide history simulations, which are located in Maokong, Taipei, are introduced. Both slopes were triggered by Typhoon Jangmi in September 2008. The results of the numerical simulation were compared to the topography profiles measured after the collapse of the two slopes. The MPM successfully simulated the runout distance of both landslides specifically. However, because soil accumulation is affected by the three-dimensional effect, the two-dimensional numerical model simulation will slightly overestimate the height of soil accumulation after the landslide. During the failure process, as the soil compresses, the pore water pressure increases and accelerates landslide. The result also shows that the soil masses of down-slope are buried to the bottom by the soil masses of up-slope. And using undrained analysis is not feasible because it limits the drainage condition of the topsoil.
參考文獻
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