| 摘要: | 1999 年臺灣中部發生集集地震，造成許多造成許多生命財產的損失。在 這次地震中，車籠埔斷層的錯動造成嚴重的地表變形至 5 公尺，且座落於 地表變形影響範圍內，可以發現大量的基礎設施與結構損壞。為了解更多斷 層錯動與設施之影響，本研究以給定屬性淺基礎與斷層錯動進行數值模擬。
本研究使用二維顆粒流分析程式 PFC2D 5.0( Particle Flow Code in Two Dimension 5.0)進行逆斷層錯動模擬。本研究參考張有毅(2013)，在 80g 下進 行砂箱試驗的數值模擬，其斷層上盤相對應的最大模型垂直位移(h)為 5 cm。本研究探討了乾砂土之逆斷層，於自由場與放置淺基礎之狀況下，在 不同地層深度位置，以土壤的應力路徑變化、主應力方向變化以及剪力破壞 之斷層錯動百分比的細部探討。此外亦將基礎載重、埋置深度以及放置位置 三種不同素，探討剪裂帶發展與基礎旋轉角，及其互制關係。
模擬結果顯示:砂性土層剪裂帶區的應力路徑變化主要受水平應力影響， 且以側向壓縮為主要路徑趨勢，由最大主應力方向來看亦是以水平應力為 主要方向。於剪力破壞之斷層錯動百分比中可發現基礎載重增加，會使基礎 下方之土層圍束效應加大，亦使該區塊需更大的斷層錯動以致破壞。而於基 礎載重加至 2 倍、基礎埋至土層以及基礎位置影響之案例中，其結果顯示: 基礎旋轉角與位置之關係(上盤近過渡帶)S/B=0> (過渡帶)S/B=0.69 > (下盤 近過渡帶)S/B=1> (上盤遠方)S/B=-2.39>(下盤遠方)S/B=3.33，而其中以基礎 放置於下盤且保持斷層露頭處約 15 公尺之距離最為安全，其他試驗中於上 盤處之基礎旋轉角較大。;In 1999, the Chi-Chi earthquake hit the central part of Taiwan and caused numerous loss of lives and properties. The offset of Chelungpu fault during this event induced severe ground deformation up to 5 m, and building failure can be found everywhere of the affected area. In order to study more of the building reaction during fault offset, we have modelled the fault offset with a shallow foundation of given properties.
The fault is modelled using the program Particle Flow Code in Two Dimensions (PFC2D). We have simulated a numerical model based on the sandbox test from Chang (2013), in which the model condition is under 80g (corresponding to maximum vertical displacement of 5 cm of the hanging wall). This study discussed the reverse fault with dry sandy soil in the condition of free field and shallow foundation. We used the way of the stress path variations, the principle stress direction and the ratio of dh/H with shear failure at different depth of the soils to investigate the result from numerical modeling. Furthermore, three different parameters, which are foundation load, embedding depth and placement position were also discussed about the interaction between the development of the shear zone and the rotation angle of the foundation in the study.
The results of the simulation show that the stress path variation of the sandy soil layer with fault rupture zone was mainly affected by the horizontal force , and the primary trend was lateral compression. Also, the results of the major principal stress direction, the horizontal stress was also the main direction in the fault rupture zone. In the other side, the ratio of the dh/H with shear failure shows that when the foundation load increase, the confining stress of the soil layer below the foundation would also increase, which required more fault displacement to cause the damage.
In the cases where the foundation loading is doubled, the embedding foundation and the foundation position affection, the results showed that: the relationship between the rotation angle of the foundation and the position was : (at the hanging wall which near the transition zone ) S/B=0 > (at the transition zone) S/B=0.69 > (at the footwall which near the transition zone) S/B=1 > (at the hanging wall far from the transition zone ) S/B=-2.39 > (at the footwall far from the transition zone) S/B=3.33. The safest position of the foundation was on the footwall, and about 15 meters away from the fault outcrop. In other tests, the foundation rotation angle at the hanging wall was larger. |
