平移斷層錯動引致凝聚性覆土地表變形與淺基礎變位特性探討

Characteristics of Ground Deformation and Shallow Foundation Displacement of Overburden Cohesive Soil Induced by Strike-Slip Faulting

翁培軒(Pei-Syuan Wong)

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(2016年)

https://doi.org/10.6342/NTU201601375

摘要

根據歷史災害紀錄，大地震發生時，斷層錯動引致上覆土破裂與變形。平移斷層錯動，地表可以觀察到不同破裂系統發展與變形行為，在近斷層帶的建築物因為這些地表變形產生旋轉、水平、垂直位移情形，同時破裂跡也會繞過剛性較強的基礎。上覆土層由膠結較差的沖積層組成，斷層破裂通過，會有變形發散的現象，覆土厚與材料強度為影響地表變形的重要因素，也間接影響結構物行為。

　　本研究使用高嶺土加水的低強度黏土，單壓強度13.58 kPa，在20 cm x 20 cm x 10cm小尺度的左移直剪盒模型，1g環境下實驗，記錄不同覆土深度、錯動量與淺基礎形式(埋置與形狀)下，影響地表破裂跡發展、地形起伏、淺基礎位置的變化，量化其結果。並由物理試驗的結果為基礎，用分離元素法建立數值模型，來討論覆土深度、錯移量與基礎埋置對地表變形的影響和基礎變位特性。

　　研究結果顯示，隨斷層錯動量增加，地表依序出現R、P、Y shears等破裂徵兆。斷層錯移量對覆土深度正規化(Db/Ds)，Db/Ds=1.2時R shears出現，與主斷層線夾15-20?；1.8時反向P shears出現，夾10- 20?，貫穿地表破裂的Y shears也同時發展。裂縫出現在R shears之間或端點，並造成陷落，靠近主斷層線R shears重疊處，地表隆起。隨錯動量(Db/Ds)增加，變形帶的寬度、裂縫面積、地表隆起量增加，直到主要變形帶寬固定。覆土厚較大，破裂跡發展需較大錯移量，且變形帶較寬。斷層線通過基礎正下方，破裂跡會繞過基礎發展。主要變形帶受基礎形狀與埋置與否影響，相同形狀有類似發展趨勢，埋置則增加變形帶寬度和地表隆起量。基礎行為，主要是逆時針旋轉與平行主斷層線的位移增加，埋置深度使基礎旋轉量減小。藉由試驗影響地表破裂變形和基礎機制的了解，將地表變形量值與錯移量、覆土厚關係應用於過去斷層資料，推得現地覆土厚度，作為驗證與考量設計上結構物與斷層的關係。

關鍵字

活動斷層 ； 平移斷層 ； 地表變形 ； 地表破裂 ； 淺基礎

並列摘要

According to investigation of recent earthquakes, ground deformation and surface ruptures were induced by faulting. The zones of horizontal and vertical surface ground deformation and different features of surface ruptures were investigated in the field. Because of the structural integrity, the surface rupture may detour the foundation. The overburden soil consists of softer material, which diffuses the strain of soil induced by faulting. The depth of soil and material properties are important factors of surface ground deformation, which influences the response of structure.
This study presents results from shear box experiment on small-scale soft clay models subjected to strike-slip faulting (fault angle 90 ?) with shallow foundations (circular and rectangular shape ) placed on it in a 1-g environment. The quantifiable data including sequence of surface rupture, ground deformation and rotation and displacements of foundation are recorded with progressive strain. Based on the results of physical tests, numerical model of distinct element method is applied to analysis the influence of depths of soil and foundation to ground deformation and characteristics of foundation dislocation.
The result of this study indicates the fracture system consists of R, P, Y shears. With increasing displacements of fault, R, P, Y shears appears sequently. Primary deformation zone (P.D.Z.) involves the surface ruptures, ground elevation and cracks. The thicker overburden soil layer causes wider P.D.Z. The shape and embedded depth of foundation have significant impacts on the width of P.D.Z. The rotation and movement along with the direction of fault of foundation increase. Due to deeper embedded depth, the rotation of foundation becomes smaller. To sum up, the macro behavior of the soil and foundation caused by faulting is surveyed, to validate the historic data and to take it considered geo-structure design.

並列關鍵字

Active fault ； Strike-slip fault ； surface ground deformation ； surface rupture ； shallow foundation

參考文獻

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