斜移斷層錯動引致上覆土層同震變形行為及對淺基礎結構物之影響

Interaction between Co-seismic Ground Deformation and the Shallow Foundation Induced by Oblique-Slip Faulting

柳鈞元(Chun-Yuan Liu)

指導教授 ： 林銘郎

國立臺灣大學/工學院/土木工程學研究所/碩士(2019年)

https://doi.org/10.6342/NTU201901677

摘要

中央地質調查所至今已公告33條活動斷層以及19個活動斷層地質敏感區，其中多條活動斷層具有三維的斜向滑移的證據，活動斷層的錯動除了造成強地動之慣性力外，基盤錯移將使上覆土層發生同震變形，地表變形破裂沿線之人工結構物遭受損壞，在斷層-土壤-結構互制關係中，因結構物勁度遠大於覆土層，地表破裂跡與地下斷層面的發展受限於淺基礎，破裂跡會沿著基礎角隅發展，不同形式的斜向錯移亦迫使淺基礎產生不同程度的水平位移與傾斜。
本研究針對斜移斷層簡化分析，使用無凝聚性砂土模擬上覆土層之材料，鋁塊作為淺基礎結構物，模擬不同形式的斜移斷層錯動，觀察地表破裂跡的發展歷程，記錄淺基礎因斜移斷層作用引致的變位與傾斜，並改變淺基礎的位置與跨斷層方向，觀察淺基礎與覆土層變形之間的互制行為，藉由比較地表變形趨勢與淺基礎變位行為，調整數值分析使用之參數來與砂箱試驗相互比對與校核，尋找淺基礎調適策略，降低地表變形破裂對淺基礎造成的衝擊。
從砂箱試驗得知走向滑移分量之雷氏剪裂與逆移分量之斷層崖線結合產生形貌複雜的破裂跡，破裂跡會沿著淺基礎角隅而蜿蜒，在斜向錯移量達0.3倍覆土厚時，淺基礎將嚴重傾斜與明顯地水平旋轉，基礎周圍覆土層亦因基礎擠壓而產生被動土壓而變形。由淺基礎與斷層的相對位置顯示，若長條形淺基礎跨斷層線的方向與斷層走向滑移方向相反將能減輕傾斜與水平旋轉的程度，若三角剪切帶未直接通過或遠離淺基礎，則淺基礎之變位將大幅降低。
現地案例模擬在集集地震中，車籠埔斷層斜向錯動通過埤豐橋南側建築群，當中三棟淺基礎結構物座落於車籠埔斷層崖上，因地表變形而明顯地傾斜與水平旋轉。藉由現地調查資料、災前後影像與新舊地籍圖，重建災前結構物形式與位置，估算車籠埔斷層抬升3.5公尺伴隨左移3.7公尺，以離散元素法軟體進行全尺度模擬，模擬顯示五棟受災結構物經歷不同程度的變位、傾斜與旋轉歷程，其中三棟嚴重受損結構物之變位與傾斜模擬結果與災後調查成果接近，亦可與小尺度試驗之受損情形對照。
整合研究成果，淺基礎之位置、跨斷層形式與斷層斜向滑移特性，均與斷層作用引致之結構物損壞有著密切的關係，斷層作用與淺基礎結構物間彼此互制。

關鍵字

斜移斷層 ； 斷層與淺基礎互制行為 ； 砂箱試驗 ； 離散元素法 ； 活動斷層

並列摘要

Central Geology Survey（MOEA）so far have announced 33 active faults. 9 of them have scientific evidences for characteristic of oblique-slip faulting. In addition to strong ground motion, co-seismic ground deformation, induced by basement offset, pose a great risk to artificial structure. Infrastructure along surface rupture would be severely damaged. However, the stiffness of foundation is large than overburdened soil layer, which restricted the propagation of underground fault slip plane and surface rupture develop along foundation’s corner. With different rake angle, foundation are force to dislocation, inclination and horizontal rotation to different degrees in oblique-slip faulting.
In this research, we placed emphasis on the oblique-slip faulting. By simplified the fault plane to be 60 degrees and assumed the overburden soil to be no cohesive sediment, downscaled sandbox tests were conducted and a rectangle metal block are serve as a embedded shallow foundation. With the help of photogrammetry, high-resolution digital surface data are obtained. In the free field, Riedel shear, induced by strike-slip offset, and fault scarp, induced by dip-slip offset combined to form a complicated rupture lineation. Shallow foundation incline and rotate more than 10 degrees when the basement oblique slip reach 0.3H （thickness of overburden soil）. The dislocation of foundation force the surrounding overburden soil to form passive deformation. In the view of adaptation, the foundation would have less damage if the long axis direction of shallow foundation opposite to the strike-slip direction. As for mitigation, the foundation should avoid from triangular shear zone as much as possible.
In 1999 chichi earthquake, chelungpu fault oblique slip in the fengyuan-shihgang area. The fault rupture line cross through a building complex, 3 buildings located within the fault zone severely inclined and rotated due to 3.5 m uplift and 3.5 m left-lateral offset. Base on previous field surveys, aerial photo and cadastral map, we reconstruct the structure type and size. We use distinct element model （PFC3D） to simulate the damage process of the building complex. The result of simulation are close to the field survey after the chichi earthquake. The position of foundation, long axis direction and oblique-slip characteristic have much effect in the interaction between shallow foundation and oblique-slip faulting.

並列關鍵字

Oblique-slip fault ； Interaction between shallow foundation and fauting ； Distinct element model ； Sandbox test ； Active fault

參考文獻

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