正斷層錯動引致上覆土層變形及其對橋梁上部結構型式及樁基礎互制之研究

The Deformation of Overburden Soil and Interaction with Pile Foundations of Bridges Inducd by Normal Faulting

吳亮均(Liang-Chun Wu)

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(2017年)

https://doi.org/10.6342/NTU201701779

摘要

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。以大台北的山腳斷層為例，其位於台北盆地西緣，為一半地塹陷落之正斷層構造，在山腳斷層上方有許多重要建設，如高鐵即在樹林段以橋梁方式跨越山腳斷層，若山腳斷層發生錯動，沉積之上覆土層，將造成地表變形，並可能使結構物發生破壞。這些結構物會為了承載之安全性採用樁基礎，近斷層帶的樁基礎受斷層錯動可能會產生旋轉、傾斜、水平、垂直位移等情形，進而造成其上部橋梁可能發生落橋的情形，因此探討正斷層錯動引致上覆土層變形及其對橋梁上部結構型式及樁基礎互制之影響，有其必要性。
本研究首先採用越南石英砂，在相對密度55%、摩擦角35˚的情況下，於砂箱尺寸長*寬*高(110*20*60 cm)進行小尺度試驗，探討正斷層在1g環境下錯動過程，上覆土層三角剪切帶、主要影響帶寬和樁基礎旋轉、傾斜、位移等物理量，以利了解上覆土層變形與樁基礎互制之主控因子，實驗結果將配合數值模擬工具驗證其合理性。
砂箱試驗結果顯示，在低斷層傾角(30˚)時，三角剪切帶會發展較多條，共有7至9條，且上、下盤皆發展多條剪切帶，主要影響帶寬會較寬；高斷層傾角(60˚)，三角剪切帶會發展較少條，共有3條，下盤發展出兩條、上盤發展出一條，主要影響帶寬會較窄；不論傾角高低皆會形成地塹；樁基礎行為則皆可掌握每組試驗的旋轉、傾斜、位移等物理量。樁基礎位於不同位置時，會影響上覆土層變形，以高斷層傾角(60˚)的試驗中為例，樁基礎位於斷層尖端上方或位於斷層下盤距尖端10 cm處時，上盤主要影響帶寬皆較寬；樁基礎位於斷層上盤距尖端5 cm處時，下盤主要影響帶寬則較寬，同時在會發展出兩個下盤主要影響帶寬；在樁基礎行為上，則是位於下盤一定距離後，受到的影響會較小。
數值模擬工具PFC 3D，將先對小尺度試驗進行擬合，並利用PFC 3D的便利性進行正斷層錯動下對橋梁及樁基礎互制模擬、不同上覆土層受正斷層錯動之差異，最後將探討實際案例-高鐵跨山腳斷層橋梁段之縮尺1/20模擬。
數值模擬結果顯示，PFC 3D可以有效擬合物理砂箱試驗，並能夠模擬橋梁與樁基礎受斷層錯動之行為，證明分離元素工具PFC 3D是有模擬斷層與結構物互制的可行性；透過PFC 3D的參數改變，能夠有效模擬砂土材料、黏土材料、複合土層材料(砂土覆蓋黏土及黏土覆蓋砂土)，其中砂土材料的主要影響帶寬為上述三者最大，黏土材料會在地表呈現張力裂縫的現象，複合土層材料地表現象則是以上層材料為主控因子；高鐵跨山腳斷層橋梁段之縮尺1/20之模擬，根據本研究所採用之參數探討，可以了解若山腳斷層的位置是通過018PR14及018PR13A之間，上部結構物發生落橋的可能性是有的，由於山腳斷層的精確位置仍須確認，應此針對本橋梁跨越山腳斷層段之上部結構安全性須持保守態度。

關鍵字

砂箱試驗 ； 數值模擬 ； 上覆土層變形行為 ； 樁基礎行為 ； 山腳斷層

並列摘要

Ground deformation induced by faulting is one of the causes for engineering structural damages in addition to strong ground motion Using the Sanchiao Fault in Taipei as an example, it is a normal fault located on the west side of Taipei Basin. There are many important structures above Sanchaio Fault, the Taiwan High Speed Rail (THSR) crossing Sanchiao Fault by bridges is an example. Once Faulting, the overburden soil will cause ground deformation and make structures damaged. The usage of pile foundations is very common as they provide the necessary bearing capacity. The piles may suffer rotation, inclination, displacement due to faulting and make the bridges collapse. Therefore, the study in The Deformation of Overburden Soil and Interaction with Pile Foundations of Bridges Inducd by Normal Faulting is a very important issue.
In this study, a small-scale sandbox model in sandy soil in relative density 55%, friction angle 35˚ is used to evaluate development of triangular shear zone, the ground deformation and the rotation, inclination and displacement of piles in 1g surroundings subjected to faulting. The experiment results are used to validate the numerical simulations.
The results in experiments indicates that the shear zone developed seven to nine in hanging wall and footwall and the wider primary deformation zone in lower fault tip angle (30˚) while the shear zone developed three in hanging wall for one and footwall for two and the narrower primary deformation zone in higher fault tip angle (60˚). However, all of them form graben subjected to faulting. We can understand the rotation, inclination, displacements in the all experiments. The pile in different locations will cause different soil deformation. Take the high fault tip angle (60 ˚) as am example, the pile above fault tip or in the footwall 10 cm, the width primary deformation zone in hanging wall will occur. The pile in the hanging wall 5 cm, the width primary deformation zone in foot wall will occur. The behaviors of pile doesn’t wok up when the pile in the foot wall for more distance.
The numerical program PFC 3D be used to validated by small-scale sandbox experiments in the first. Then, bridges simulations, different soil simulations be simulated. The end, study real case “THSR crossing Sanchiao Fault by bridges” in 1/20 scale simulation.
The simulations indicate, the PFC 3D have effective to calibrate from sandbox experiments and it can simulate the piles and bridges subjected to faulting. There have practicability to simulate faults and structures from PFC 3D. Through the change of parameters in program, it can simulate different overburden soil such as sandy soil, clay, complex soil. The sandy soil has the widest primary deformation zone. The clay has tension crack on the surface. The surface appearance is controlled by upper material from complex soil. According to the paramters in this study, the “THSR crossing Sanchiao Fault by bridges” simulations, it can understand that if the locations of Sanchiao Fault crossing between 018PR14 and 018PR13A, it has the possibility collapse of superstructures. Since the accurate location of Sanchiao Fault is uncertain, the safety of superstructures of bridges needed to be considered more careful.

並列關鍵字

Sandbox Experiments ； Numerical Simulations ； Deformation of Overburden Soil ； Behaviors of Piles ； Sanchiao Fault

參考文獻

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