正斷層錯移對上覆砂土層之變形行為探討

Deformation in sandy soil during normal faulting

蔣佳興(Chia-Hsing Chiang)

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(2006年)

https://doi.org/10.6342/NTU.2006.01737

摘要

摘要

世界上著名地震性災害之調查結果發現，如1999年土耳其Izmit地震(Mw=7.4)及我國之集集地震(Mw=7.6)等，靠近斷層之結構物損害皆相當嚴重。如此的損害除受到強地動之慣性力作用外，另一主要原因即為斷層錯動後上覆地層之變形。因土層之差異變形使結構物產生破裂或是翻倒，而造成相當大的損失。若對斷層錯動後對上覆土層之變形行為有所掌握，則能更加完善地規劃近斷層之土地利用。

本研究方法以小比例尺之物理砂箱模型，及材料性質較能掌握且質地均勻之石英砂，模擬正斷層錯動引致上覆砂土層之變形行為，透過攝影記錄，觀測剪切帶之發展情況。另一方面，對於砂箱實驗所得之結果，利用有限元素分析軟體(ABAQUS)進行模擬比對，期能對小尺寸之砂箱力學行為有所了解，進而推演至全尺寸之現地模擬，以掌握土層變形情況。

本研究於物理砂箱試驗方面主要探討1.不同斷層傾角對土層變形之影響、2.不同覆土層厚度對土層變形之影響及3.地塹區域之土層變形情況。物理砂箱試驗結果顯示：
1.覆土厚度20cm，高斷層傾角試驗中，砂土層僅於下盤側發展剪切帶；而在低斷層傾角試驗中，上盤及下盤側上方之砂土層皆有產生剪切帶，影響範圍較高傾角之範圍來得大。
2.剪切帶發展會受不同覆土厚度影響：低覆土試驗下，剪切帶僅於下盤側上方發展；高覆土試驗中，於上盤及下盤側上方皆有發生剪切帶。
3.由物理砂箱試驗結果得知，剪切帶是由錯動處向外擴展。觀察剪切帶左右兩側砂土之變形情況，可用以評估剪切帶之活動性。
數值模擬方面：利用數值分析軟體，進行同物理模試驗條件之相關模擬，分析結果顯示:
1.利用數值工具能有效模擬因正向錯移下砂土之最危險區域。高斷層傾角及低斷層傾角之塑性應變集中區，皆與物理砂箱模型之剪切帶範圍相當。
2.數值模擬中，可以利用應力路徑來檢視網格受力情形；研究中得知上盤側之網格較下盤側來得危險。
3.全尺寸數值模擬結果：於現地剖面之數值模擬，塑性應變帶之範圍距選擇之工址約75m，就塑性應變帶分佈來看，此工址並沒有位於最危險之區域。如果山腳斷層崖是以低傾角之情形向下錯移，於上盤側將會產生剪切帶，對於工址之安全性則需謹慎考量。

關鍵字

正斷層 ； 物理砂箱試驗 ； 數值分析 ； 山腳斷層

並列摘要

Abstract
When normal fault slips, especially triggered by earthquakes, the deposit alluvium may deform and a fault zone also develops within itself. The deformation in alluvium might bright terrible damage to overground and underground structures. So, to find the deformation range of overburden soil and locate the fault rupture is an essential issue to evaluation the safety of ground or underground structures near the potential faulted zone. On the basis of previous research by Cole and Lade (1984), this research further explores the processes of noraml faulting within the sandy soil, studying the influences of corresponding factors or parameters and the range of influential zones using physical model tests and numerical analysis for both small-scale and full-scale. Moreover, this study collected field case near Sanchiao fault in Taipei basin, useing numerical analysis to find out the damage zone.
The experimental results indicate different fault dip angle influence the range of damage zone. In the low dip angle test, failure surface develop both side of upthrow and downthrow. The range of failure zone is larger than the high dip angle test. The result of the low dip angle test, it develop the structure of graben which only occurred in normal faulting.
In small-scale analysis, the numerical simulation tends to have similar result as those of sandbox experiments, include the range of influence zone and location of the surface rupture. Among stress paths exploration, the damage zone is reach failure criteria, it could understand where the worst zone is. In the study, the tension zone occurs primarily in the highly disturbed upthrown block. In full-scale analysis, it is a useful numeral analysis to judge the structure in the damage zone or not.
The numerical analysis program is a helpful tool to quantity the deformation of soil during normal faulting. In the future, more analysis of filed case can understand the influence zone of Taipei basin near Sanchiao fault. It can supply designers to improve the safety of the structure, and far from the damage zone.

並列關鍵字

noraml fault ； sand box tests ； numerical analysis ； Sanchiao fault

參考文獻

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