逆斷層作用與土層內樁基礎之互制關係

The Interaction between Thrust Faulting and Pile Foundations in Soil

吳杰祐(Chieh-Yu 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(2008年)

https://doi.org/10.6342/NTU.2008.01702

摘要

在1999年集集地震之斷層帶附近，可以觀察到許多因斷層錯動引致上覆土層變形影響到的橋樑錯移、維生管線破壞等，都對生命財產帶來了極大的損失。根據在大甲溪、烏溪、濁水溪水系區域所統計因受地震而損壞的橋樑就有27座之多，而正在興建的國道三號高速公路，在南投地區也有多段高架橋因受震災而損毀，另外還有如名間的高壓鐵塔受到斷層錯動傾斜位移失去其功能性。這些結構物或橋樑，為了穩定性和安全性採用了深基礎，但也有少數的樁基礎僅受到些微的位移不受影響，因此討論樁基礎與逆斷層錯動的互制關係，可以用來作為在近斷層區域土層中樁基礎規劃的參考，應為值得研究的議題。
集集地震活動的斷層型態為逆斷層，因此本研究針對逆斷層做探討，使用無凝聚性的砂土及厚紙板來模擬砂箱試驗內的上覆土層材料及樁基礎。進行室內的小尺度砂箱試驗，去探討逆斷層錯動時引致上覆土層的變形與樁基礎的互制行為，並以砂箱試驗之材料性質與配置，當作參數來進行數值分析，以測試與檢核數值分析工具的合理性，當小尺度的數值分析能與砂箱試驗吻合後，透過全尺寸的數值分析來模擬當斷層錯動引致上覆土層變形的行為，以及其與樁基礎的互制關係影響。
目前的研究成果，透過砂箱物理試驗跟數值模擬分析的疊圖比較，由數值模擬中塑性應變帶發展的區域與砂箱試驗斷層面比較，可以利用數值模擬工具有效的模擬出剪切帶位置跟樁基礎受到的影響，因此驗證了此數值分析工具的可行性，在斷層錯動後其上覆土層變形範圍與樁基礎所受到的影響，可以發現到剪切帶受樁基礎的影響，產生一條繞過樁基礎下方的剪切帶，以及一條從樁基礎下方開始往上盤發展的背衝斷層，此背衝斷層也是被認為對樁基礎的位移和傾斜的主要影響之一，可以將此數值模擬模式用來預測樁基礎跟斷層剪切帶的相對位置關係，分別會對斷層剪切帶以及樁基礎產生何種程度的影響。
在探討樁基礎位置與剪切帶的關係時，我們可以初步瞭解到，當樁基礎沒有與剪切帶相交時，樁基礎跟剪切帶不會產生互制關係，而當樁基礎置入在剪切帶內時，樁基礎跟剪切帶會開始產生互制關係，剪切帶的發展會受到樁基礎的影響而改變其路徑，推使樁基礎上盤的土層抬升高於下盤處的土層，被動土壓力的增高使得樁基礎的傾角開始增大；並會產生一條繞過樁基礎下方發展到下盤地表面的剪切帶，使得地表水平錯動範圍會寬於沒有樁基礎的型態，當樁基礎位於剪切帶內且深度越深時，剪切帶的發展會受到深樁基礎的影響而產生較大的改變，地表水平錯動範圍會變大，樁基礎傾角也會增大。
進一步的探討雙樁與剪切帶的關係，兩個樁基礎間的相對距離會影響剪切帶的發展，當兩個樁基礎之間距離較近時（本研究案例5cm），兩個樁基礎會形成一範圍較大類似墩基礎的系統，塑性應變帶不會發展到兩個樁基礎中間的區域，而塑性應變帶的發展類似單一樁基礎，但受到此較大墩基礎的影響，樁基礎的傾角會比單一樁基礎時小；而當兩個樁基礎的距離在一適當範圍（本研究案例10cm∼15cm），塑性應變帶會發展進入兩個樁基礎中間的區域，並在兩個樁基礎下方皆會產生一背衝斷層，使得樁基礎的傾角會比單一樁基礎時大；當兩個樁基礎的距離超過一定範圍（本研究案例15cm），另一個樁基礎並不會與背衝斷層區域相交，因此塑性應變帶的發展就會類似單一樁基礎時的情形，樁基礎受到的傾角跟單一樁基礎時也類似。
數值模擬名間高壓鐵塔受斷層錯動而傾斜的現地案例成果，可以看到塑性應變帶的發展，有發展出一條繞過樁基礎下方的剪切帶以及背衝斷層，造成樁基礎的傾斜跟位移，而受到上盤的覆土層深度較淺，以及樁基礎貫入深度較深的關係，在基盤尖端跟樁基礎之間發展出一破壞程度較大的塑性應變區，另外在上盤處發展出多條背衝斷層，使得地表受到影響的水平錯動範圍增大許多，可以所見在現地情況裡，覆土深度不一定是都維持水平一致的，當覆土深度不同時，會使得剪切帶發展產生不同的情形，可能使得破壞區域增大。

關鍵字

車籠埔斷層 ； 砂箱試驗 ； 數值分析 ； 三角形剪切帶 ； 樁基礎

並列摘要

Chichi earthquake fault patterns for the activities of the thrust fault, so this study to explore thrust fault, the use of non-cohesion sand and thick cardboard to simulate the overburden soil and pile foundation in sandbox test. The small-scale sandbox test to probe into the thrust fault dislocation caused by the deformation of the soil and pile foundation of the inter-system, and uses the material properties and configuration of sandbox test as a parameter to numerical analysis, to test the reasonableness of the input parameters. When the small-scale numerical analysis to test anastomosis with the sandbox test, through full-size numerical analysis of the fault to simulate the dislocation caused by the deformation of the soil layer, and with pile foundation of relations of mutual influence.
At present the research results through the sandbox test with the numerical simulation of the overlapping plans, by the numerical simulation of plastic strain with the development of regional and sandbox test fault shear zone comparison, the use of numerical simulation tools can be effective simulated shear zone location with the impact on the pile foundation, this proved the feasibility of numerical analysis tools, after their fault dislocation on the deformation of the soil layer and pile foundation by the impact, we find that the shear zone base on the impact of the pile foundation, it develops one bypass the bottom of the pile foundation shear zone, and one from the bottom of the pile foundation for the development to hanging wall of the back thrust fault, this back thrust fault is that the displacement of the pile foundation and tilt the main impact. This numerical simulation models can be used to predict pile foundation fault shear zone with the relative position, respectively, will fault shear zone and a pile foundation of the extent of impact.
In piles on the basis of location and the relationship between the shear zone, we can understand that initially, when the pile foundation does not intersect with the shear zone, the pile foundation with shear zone system does not produce mutual relations, and when placed in the pile foundation shear zone within, the pile foundation with the shear zone will begin to generate interaction, the development of shear zone will be the impact of pile foundation to change its path, it will develop one back thrust fault at hanging wall of the pile foundation, this pushing on the hanging wall soil of the pile foundation was higher than the footing wall soil of the pile foundation, increasing the pressure on the passive soil pile foundation makes the angle started increasing. And will have a bypass the bottom of the pile foundation development the shear zone to the footing wall surface, making the surface level of dislocation will be wider than the pattern of free field, when the pile foundation in the shear zone, and the depth of the deep, the shear zone will be the development of deep-pile foundation and have a greater impact changes in the level of dislocation of the surface will become wide, pile foundation inclination will increase. Further explore the relationship with the shear zone and two-pile foundations, the relative distance between two-pile foundations will affect the development of shear zones, when the distance between the two pile foundation at the close (in the case study 5cm), Two piles will form the basis of a larger scope of a similar system based on the pier, the plastic strain will not bring development to the two pile foundation central regional, and the plastic strain with the development of a similar basis alone, but by the larger impact of the pier foundation, the inclination of this pile foundation is smaller than the basis of a single pile foundation .When the distance between the two in an appropriate range (in this case study 10cm∼15cm), plastic strain will bring development into central region between two pile foundations and below the two pile foundation will have a back thrust fault, making the pile foundation inclination than a single large foundation, when the distance between the two pile foundation exceed certain limits (in this case study 15cm), another pile foundation and will not be intersection with the back thrust fault regional, with the plastic strain development will be similar to the basis of a single case, the pile foundation by the angle with a single foundation also similar

並列關鍵字

the Chelungpu fault ； sand box test ； numerical analysis ； triangular shear zone ； pile foundation

參考文獻

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