地下室基礎與上覆土層受正斷層錯動之互制行為

Interaction between Basement Foundation and Overburden Soil Subjected to Normal Faulting

方儒雅(Ru-Ya Fang)

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(2021年)

https://doi.org/10.6342/NTU202103126

摘要

近年的地震事件顯示除了強地動之外，斷層錯動造成的同震地表變形也是斷層附近結構物產生破壞的原因。台灣人口稠密，建築用地無可避免的會與斷層帶有交集，例如屬正斷層的山腳斷層鄰近台北盆地，斷層帶上有許多高樓結構物使用筏式基礎搭配連續壁（即地下室基礎），連續壁向下延伸增加了土層與基礎互制之複雜性，進一步加深量化評估地下室基礎與上覆土層受正斷層錯動之影響的難度。
為有效降低斷層錯動可能形成的災損，本研究使用基於有限差分法耦合離散元素法的三維數值模型（FLAC3D），離散元素法模擬受正斷層錯動下產生應變集中帶的上覆砂土層，有限差分法則模擬筏式基礎結構物因斷層錯動和地表變形產生的反應。為了確認此耦合分析方法能合理模擬上述複雜課題，本研究建立三個簡化的驗證模型，也進行一系列的縮尺砂箱實驗與數值模擬結果相互校核，最後透過馬拿瓜中央銀行於1972 年地震中，地下室與斷層跡互制之歷史案例模擬來確認分析方法能合理地應用於全尺度現地案例。
基礎中心與斷層尖端之相對位置為本研究之主要變因，地下室基礎的重量有效壓制主斷層帶發育，連續壁的向下延伸使斷層帶不易進入基礎底部，而是發生轉向或分岔，地下室基礎旋轉會導致連續壁周圍土層產生主、被動破壞；地下室基礎反應方面，由於斷層擾動基礎底部土層導致基礎底部失去部分反力，產生不均勻沉陷與角變量，連續壁抑制基礎旋轉，同時受上下盤塊體拉張產生向外彎曲，與斷層直接接觸之連續壁需承受更大的彎矩。
根據研究成果，本研究建議在設計結構物配置時若無法保持距離，靠上盤側配置長形基礎（長軸與斷層破裂跡垂直配置）能受較少影響，數值模擬能預估可能產生破壞的位置及形式，於基礎設計中加入調適行為，減少其受地表變形之損害。

關鍵字

正斷層 ； 同震地表變形 ； 地下室基礎 ； 上覆土層變形與基礎互制 ； FLAC3D ； 耦合有限差分法與離散元素法

並列摘要

Recent earthquake events have shown that besides the strong ground motions, the coseismic faulting often caused substantial ground deformation and destruction of near-fault structures. In Taiwan, many high-rise buildings with raft foundation are close to active faults due to the dense population. The Shanchiao Fault is a major active fault that poses potential dangers to the capital of Taiwan (Taipei). This study applies coupled FDM-DEM analysis on the soil-raft foundation interaction subjected to normal faulting. The coupled FDM-DEM approach includes two numerical frameworks: the DEM-based model to capture the deformation behavior of overburden soil, and the FDM-based model to investigate the responses of raft foundation. The analytical approach was first verified by theoretical solution, empirical solution and physical experiment. A series of small-scale sandbox model was conducted to validate the deformation behaviors of overburden soil and structure elements in coupled FDM-DEM model. In order to apply the analytical approach to a real case, the full-scale numerical models were then built to understand the effects of relative location between the fault tip and foundation in the normal fault-soil-foundation behavior.
The results show that the weight of foundation and the depth of diaphragm wall can efficiently prevent structural rotation and resist the fault develop, then it deflects and bifurcates instead. For the foundation response, the fault disturb the soil that under the foundation and let the foundation loss part of support, uneven settlement and angular distortion occur at the same time. The diaphragm wall can deduce the foundation rotate, while the tension stress accumulates at the connection and bottom of the diaphragm wall. The raft foundation located above the fault tip suffers greater displacement, rotation, and inclination due to the intense deformation of the triangular shear zone. Overall, the failure mechanism observed in numerical simulation can provide a good reference in foundation design. Based on the results, we suggest different adaptive strategies for the basement foundation located on the hanging wall if the buildings are necessary to be constructed within the active fault zone.

並列關鍵字

Coupled FDM-DEM approach ； normal faulting ； ground deformation ； soil-foundation interaction ； basement foundation

參考文獻

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