飽和砂中模型樁之側向載重試驗

Lateral Loading Test on Model Pile in Saturated Sands

林昌良(Chang-Liang Lin)

指導教授 ： 陳正興

國立臺灣大學/工學院/土木工程學研究所/碩士(2011年)

https://doi.org/10.6342/NTU.2011.02559

摘要

本研究利用模型鋁管樁側向載重試驗，探討緊砂中樁材於彈性及進入非線性反應下之樁-土互制行為。
本研究共進行了二組試驗，樁頭反覆側位移5 mm試驗及樁頭側位移70 mm試驗。前項試驗側向位移小，整個荷載過程中樁材處於彈性狀態，而後項試驗側位移大，荷載過程中樁材會由彈性進入非線性狀態。為取得樁斷面非線性撓曲性質，利用鋁管兩點荷重彎曲試驗建立樁斷面之非線性彎矩-曲率關係。
在側向載重試驗過程中利用樁身應變計量測樁身應變，將應變除以樁徑可得樁身曲率；配合彎曲試驗之斷面撓曲性質，可求得樁身彎矩分佈。進一步針對此彎矩分佈，以四次多項式進行曲線擬合，採用最小二乘法最佳化技術求取函數之待定係數，並配合拉格朗日乘數法處理函數邊界之束制條件。將曲率函數及彎矩函數分別積分及微分，以推求樁身變位與土壤反力分佈，進而建立土壤之p-y曲線，並歸納出此樁-土系統之p-y曲線特性參數。在求取p-y曲線的分析過程中發現，當樁斷面行為進入非線性後，應將實際斷面之非線性特性納入考量，若仍以線性撓曲剛度計算時，將會導致不正確之樁身彎矩分佈，進而發展出不合理之p-y曲線。此外，本研究進一步以試驗求得之p-y曲線來檢討常見之砂土p-y曲線模式之適用性，並與前人研究比較，觀察相同砂土在緊密與疏鬆情況下，其p-y曲線間的差異。
最後，利用SAP2000程式進行側向載重試驗之數值模擬分析。數值模型採用溫克基礎模式模擬樁-土系統，以梁元素模擬樁並於元素中設置分佈塑鉸模擬樁材非線性行為，以彈簧模擬土壤反力，根據試驗p-y曲線定義彈簧性質，並利用梅新規則模擬土壤之遲滯反應，藉由數值分析方式驗證試驗分析結果。

關鍵字

模型樁 ； 側向載重試驗 ； 回歸分析模式 ； p-y曲線 ； 樁-土互制 ； 彎曲試驗

並列摘要

Two lateral load tests on a model aluminum pile buried in saturated dense sands were conducted and analyzed in this study. The tests were performed at the National Center for Research on Earthquake Engineering (NCREE) of Taiwan. The first test was a displacement-controlled cyclic test with displacement amplitude of 5 mm at the pile head. The second test was a monotonic load test up to a maximum displacement of 70 mm at the pile head. The lateral displacement of the first test was small and the pile response was elastic during the whole loading process; the lateral displacement of the second test was large and the pile response gradually moved from the elastic state to the inelastic state with lateral loading. Besides, a two-point bending test on the model pile itself was conducted to obtain the nonlinear moment-curvature relationship of the model pile.
On the basis of the beam theory, the pile responses, including the deflection, slope, moment, and shear force of the pile shaft, and the corresponding soil reactions are computed using the strain measurements from the strain gauges on the pile. Collecting the pile displacements and soil reactions deduce the p-y curves. In the process of developing the p-y curves, it is found that the actual nonlinear property of the pile section is essential to deduce correct p-y relationships. This study also compares the characteristics of the p-y curves in dense sand with those in loose sand.
Finally, the program SAP2000 is used to simulate the lateral load tests. The numerical model uses the Winkler-beam model to simulate the pile-soil system. The results of simulation are satisfactory.

並列關鍵字

Model Pile test ； Lateral load test ； Regressive analysis ； p-y curve ； Pile-soil interaction ； Bending test

參考文獻

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