台灣位處歐亞大陸板塊與菲律賓海板塊之交界，工程設計經常要考慮地震的作用，近年如台灣集集大地震、中國汶川大地震、日本福島大地震等活動斷層造成的災害，均使生命財產遭受嚴重損害。為了探究斷層錯動對地表與地下結構的作用，在過去通常由地工離心機進行物理試驗，然而進行物理試驗相當費時且昂貴，因此近幾年許多研究考慮使用有限元素法(Finite Element Method)與離散元素法(Discrete Element Method)等數值方法進行模擬，本研究參考張有毅(2013)、Chu et al., (2015)利用離散元素法對斷層外部特性的研究，藉由此法進一步探討斷層之力學與微觀組構之變化。
本研究中，參考張有毅(2013)砂箱試驗之數值模型，使用PFC2D(Particle Flow Code in Two Dimension)在80g下進行砂箱試驗模擬，其最大垂直位移(h)為5cm。為了得知應力在模型中不同位置的變化，將模型按照深度分成淺、中、深三層，再依照位置分成上盤、過渡區、下盤三個區域，依此原則設置觀測圓讀取數據。而模擬結果顯示，模型中應力狀態主要受斷層側推力、邊界效應與剪裂帶發展影響，其中側推力與邊界效應給予模型水平應力增量，為控制模型內主應力方向最主要因素，剪裂帶影響區域主要在過渡區內。為了進一步了解斷層錯動時微觀組構與應力狀態間的關聯，首先在孔隙的變化以及體積應變的分析中，可發現剪裂帶發生時顆粒排列狀態會發生變化，使得應力狀態變得相當複雜，最後透過剪應變分析，探討斷層模擬中的破壞行為，希望藉此更了解斷層之潛在威脅。

Taiwan is located at the junction of the Eurasian plate and the Philippine Sea plate. Engineering design often takes into account the effects of earthquakes. In recent years, such as Taiwan Chi-Chi earthquake, China Wenchuan earthquake, Japan Fukushima earthquake and other active faults caused serious damage to life and property. In order to explore the effect of fault on the surface and underground structure, physical tests were usually carried out by Centrifuges in the past. However, physical test is time-consuming and expensive. Therefore, many studies consider the use of Finite Element Method (FEM) and Discrete Element Method (DEM) to simulate in recent year. However, when the fault deformation is too large, the FEM will have a greater error, so in order to get results that are more accurate, this study used DEM for reverse fault simulation.
This study referred to the numerical model of sandbox test from Chang (2013). A sandbox test with a maximum vertical displacement of 5cm was simulated at 80g by using PFC2D (Particle Flow Code in Two Dimensions). In order to understand the stress changes in different locations, The model in accordance with the depth into shallow, medium and deep, and then in accordance with the horizontal position into the hanging wall, the transition zone, the footing wall. Then, set the measurement circle by the above principle. The simulation result show that the lateral force of the fault, the boundary effect and the development of the shear zone mainly affected the stress state. Lateral force and the boundary is the most important factor in controlling the principal stress direction. The shear zone mainly affect the transition zone. In order to further understand the relationship between the microstructure and the stress state during fault offsetting, in the analysis of pore change and volumetric strain, it could be found that the state of particle arrangement changed, when the shear zone occurred, stress state became quite complicated. Finally, we discuss the destructive behavior in fault simulation through the shear strain analysis, and hope to know more about the potential threat of fault.

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