跨活動斷層橋梁基礎互制行為研究

The Research on Interaction of Bridge Foundation Across Active Fault

李健宏(Chien-Hung Li)

指導教授 ： 林銘郎

國立臺灣大學/工學院/土木工程學研究所/博士(2019年)

https://doi.org/10.6342/NTU201901420

摘要

根據近幾年來世界上幾個著名災害性地震之調查結果，顯示近斷層結構物受到地震破壞之原因，除了強地動之慣性力外，另一主要因素為基盤錯動所導致之上覆土層變形。對於跨越活動斷層的橋梁，其群樁或沉箱基礎位於變形之上覆土層中可能導致損壞，並對上部結構產生損壞。1999年發生之九二一集集大地震（Chi-Chi earthquake）造成中部地區災情慘重，大地於瞬間隆起、橋梁嚴重塌陷，其中有7座橋梁恰好通過斷層，其主體損害造成落橋或嚴重龜裂，顯示跨斷層地震對橋梁結構安全頗具威脅。在本研究中利用小尺度的物理砂箱試驗以及採用離散元素模擬軟體（PFC3D）進行數值分析，了解跨活動斷層橋梁的互制行為。當數值分析可以合理且完整的校核物理試驗結果後，再利用歷史跨越活動斷層的橋梁損壞案例事件校核全尺度數值模型，並進一步預測未來發生一定規模地震之跨活動斷層橋梁行為，以作為規劃設計之參考。
本研究針對逆斷層，使用無凝聚性砂土模擬上覆土層之材料，中空發泡聚乙烯珍珠棉管作為基樁，黏貼應變計測定變形特性，探討逆斷層錯動時，上覆土層變形行為及對群樁基礎之影響，並以砂箱試驗配置與試驗所得之材料參數進行數值分析，以測定邊界條件及輸入參數之合理性。小尺度砂箱試驗與數值分析結果在上覆土層中斷層面的傳播路徑、三角剪切帶的發展、地表變形特徵以及樁帽位移、旋轉和群樁樁身的變形方面具有良好的一致性。斷層面的發展受到群樁的存在和位置的影響而有所改變，且基樁樁帽因而呈現不同程度之旋轉和位移，進而基樁樁身產生不同程度的引致軸力和彎矩，此與上盤土體施加於基樁與樁帽之被動土壓力密切相關，值得注意的是相鄰的基樁呈現出不同的變形行為，位於三角剪切帶之群樁基礎有較大的變形。
全尺度跨活動斷層橋梁數值分析，分別以埤豐橋跨越車籠埔斷層、花蓮大橋跨越嶺頂斷層及田寮三號高架橋跨越車瓜林斷層（或稱龍船斷層）等三個歷史事件校核數值模型；國道四號潭子高架橋（興建中）以及鐵路大甲溪橋（復建工程）等二座橋梁跨越三義斷層作為預測未來發生一定規模地震之案例，提供調適策略之運用研擬。分析成果顯示，橋梁線型與斷層走向相交角度、橋墩及基礎位置、基礎的型式（基樁、沉箱）以及上部結構型式（簡支梁、連續梁）均與斷層作用導致損壞程度有著密切的關係。

關鍵字

逆斷層 ； 砂箱試驗 ； 分離元素法（PFC3D） ； 斷層與橋梁結構互制

並列摘要

Investigations on famous disasters that have occurred worldwide over recent years revealed that the reasons contributing to damages in structures near faults during earthquakes included the strong inertial force caused by strong ground motion as well as overburden deformation caused by basement displacement. For bridges spanning active faults (hereafter referred to as fault-spanning bridges), if their group pile or caisson foundations are located in deformed overburden, said foundations may be damaged and cause damage in the superstructure of the bridges. In this study, a small-scale physical sandbox experiment is performed, and a numerical analysis is conducted using discrete element simulation software PFC3D. As soon as the results of the sandbox experiment is reasonably and completely verified by using the numerical analysis, a full-scale numerical model is verified by using data from historical fault-induced bridge damage incidents to predict the behavior of fault-spanning bridges during future large-scale earthquakes. Such prediction may serve as references to relevant units when planning and designing bridges in the future.
To simulate thrust faulting, this study used non-cohesive soil as the material (to form overburden soil) and polyethylene hollow foam tube as the foundation piles. A strain gage is affixed to the soil to measure the deformation characteristics and show the effect of overburden deformation on group pile foundation when thrust fault displacement occurred. A numerical analysis is performed on material parameters (obtained from the sandbox experiment as well as from setting up the experiment) to determine the feasibility of the boundary conditions and input parameters. The fault propagation path in the overburden soil, trishear zone development, surface deformation characteristics, pile cap displacement, and group pile deformation obtained from the sandbox experiment are consistent with those obtained from the numerical analysis. Fault development is influenced by the presence and location of group pile. Additionally, foundation pile cap displayed varying degrees of rotation and displacement, causing the foundation piles to generate varying degrees of axial force and bending moment. Such axial force and bending moment are related to the pressure exerted by lateral soil pressure on foundation piles and the pile cap. Adjacent foundation piles exhibited different deformation behaviors, and group pile foundation in the trishear zone displayed relatively large deformation.
This study conducted a full-scale fault-spanning bridge numerical analysis for three disasters, which involved the Pifeng Bridge (spanning the Chelungpu Fault), Hualien Main Bridge (spanning the Lingding Fault), and Tianliao No. 3 Viaduct (spanning the Chekualin Fault, also known as the Lungchuan Fault) to verify the numerical model. Subsequently, this study predicted the behavior of the Tanzi No. 4 Viaduct (under construction) and Dajia River Iron Bridge (under reconstruction), both of which span the Sanyi Fault, if exposed to future large-scale earthquakes, on the basis of which adaptive strategies are devised. The analysis results showed that bridge line type, fault direction and intersection angle, bridge pier and foundation location, foundation type (e.g., foundation piles and caissons), and superstructure type (simple beams and continuous beams) are all closely related to fault-induced damages.

並列關鍵字

thrust fault ； sandbox experiment ； discrete element method（PFC3D） ； fault and bridges interaction.

參考文獻

Agisoft LLC, 2016. Agisoft PhotoScan User Manual professional edition, version 1.2.5.

Anastasopoulos, I., Gazetas,G., ASCE. M., Bransby. M. F., Davies. M. C. R. and EI Nahas. A. 2007. Fault rupture propagation through sand: finite-element analysis and validation through centrifuge experiments. Journal of Geotechnical and Geoenvironmental Engineering 133, 943-958. DOI: 10.1061/ASCE1090-0241,133:8(943).

Anastasopoulos, I., Gazetas,G., ASCE. M., Bransby. M. F., Davies. M. C. R. and EI Nahas. A. 2009. Normal fault rupture interaction with strip foundations. Journal of Geotechnical and Geoenvironmental Engineering 135, 359-370.

Anastasopoulos, I., Gazetas,G., Drosos. V., Georgarakos. T. and Kourkoulis. R. 2008. Design of bridges against large tectonic deformation. Earthquake Engineering and Engineering Vibration 7, 345-368. DOI: 10.1007/s11803-008-1001-x.

Anastasopoulos, I., Kourkoulis,R., Gazetas,G. and Tsatsis, A. 2013. Interaction of piled foundation with a rupturing normal fault. Geotechnique, 63, 1042-1059.