Deformation Behavior of Different Overburden during the Thrust Fault
Date Issued
2006
Date
2006
Author(s)
Wei, Yung-Fan
DOI
zh-TW
Abstract
斷層錯動引致上覆沖積土層之變形研究，其方法可分為現地調查、物理模型試驗以及數值分析等三類。在物理模型試驗方面，上覆土層大多以均質土層為考量：如Cole and Lade(1984)、林銘郎等人(2004)等以均質砂土層及Bray(1990)以均質黏土層進行物理試驗，然而，真實之沖積土層(如台北盆地之松山層)以及921地震之後其竹山交流道南側進行的槽溝挖掘調查結果顯示，斷層之上覆沖積層乃由數種不同性質之土層所構成，因此，本研究在模型試驗上欲更加接近真實沖積土層之情形，除了以均質土層(砂土層、黏土層)進行斷層錯動之模型試驗外，並採用砂黏土互層進行之，同時與數值分析模擬之結果加以比對。
物理試驗覆土層之材料計有純砂、純黏土及砂黏土互層三種，試驗目的在於探討剪切帶之發展演化趨勢、整體之變形行為與影響範圍等，均質黏土層之試驗結果將與均質砂土層作一相互比較。互層試驗為砂土層在上層而黏土層在下層，土層厚度皆為10cm，其結果將與均質土層試驗做比對。同時，就數值分析所得，均質黏土層與砂黏土互層之應力路徑進行破壞機制之探討。
試驗結果顯示，均質黏土層受斷層錯動產生之剪切破裂，其觀察到之發展順序與Bray(1990)相似；而均質砂土層剪切帶發展順序為由上盤向下盤遷移；砂黏土互層之試驗結果其黏土層形成單斜褶皺變形，而砂土層則產生兩條剪切帶。均質土層與互層物理試驗與數值模擬之比對相當，由數值分析所得之應力路徑可知：黏土層上盤部分靠近錯動處之地表面產生張力破壞；互層中砂土層與黏土層，雖然受力行為不同，但由斷層錯動產生之破壞方式皆以剪力破壞為主。影響範圍方面，均質砂土層、均質黏土層、砂黏土互層數值分析所得之影響範圍與物理試驗所得相當，皆為砂土層大於黏土層與互層，而黏土層與互層之影響範圍相近。不同土層材料之斷層擴展形式與影響範圍均不相同，若地中或地面存在結構物，對結構物所造成之損壞程度亦不相同。此外，在驗証數值分析工具之可行性後，未來可再以數值分析模擬全尺寸之逆斷層錯動，進行更詳細之定量分析。
The methods to study the process of fault propagation and the associated soil deformation during a fault offset event, include field investigations, physical model experiments and numerical analysis. The previous physical model studies of fault rupture propagation have modeled the earth materials overlying the base rock fault as cohesionless soil (e.g., Cole and Lade 1984; Lin et al 2004) and cohesion soil (e.g., Bray 1990). However, the evidences obtained from deformation of actual trust faulting (Chushan, Nantou County, Taiwan.) and Sungshan sublayer of the Taipei Basin, show the alluvium composed of numerous subsoil layers. In order to realize the deformation behavior of alluvium during a fault offset event, this model experiments of simulating thrust fault offset were set up, in which cohesionless sands, saturated clays and interbedded layer (composed of the sandy layer and the clayey layer) were adopted simulating near surface soil.
The results, obtained from experiment studies and numerical analysis based on finite element method were compared to explore the behavior of soil during faulting process. The soil deformation obtained from numerical analysis complies with the outcome from model experiments. This research further discusses the range of influential zones using physical model tests and numerical analysis. Meanwhile, the stress paths obtained from numerical analysis were explored.
The experimental results indicate, rupture developments of the clayey layer in sequence are similar to Bray (1990). In sandy layer, one major fault zone can be developed, and sub-branch fault also be developed. The clayey layer of interbedded layer was developed in front of the blind fault tip, and is one kind of fault-propagation fold; the sandy layer was developed the two fault zone. Among stress paths exploration, the tension zone occurs primarily in the highly disturbed upthrown block in clayey layer. The main failure of interbedded layer is shear-failure. At the range of influential zones, the sandy layer is farthest, and the clayey layer is closed to the interbedded layer.
In the future, a numerical stimulation can provide helpful quantity analysis and can serve as a handy tool for the earthquake resistance design.
Subjects
物理模型試驗
數值分析
砂黏土互層
剪切帶
影響範圍
單斜褶皺變形
應力路徑
model experiments
numerical analysis
cohesion soil
alluvium
interbedded layer
the range of influential zones
stress paths
fault-propagation fold
Type
thesis
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