基樁軸向承載之依時行為; Time-dependent Behavior of Axially Loaded Pile

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题名:	基樁軸向承載之依時行為;Time-dependent Behavior of Axially Loaded Pile
作者:	梁能;Neng Liang
贡献者:	土木工程研究所
关键词:	對應原理;t-z曲線;潛變;樁基礎;模型試驗;直剪試驗;correspondence principle;t-z curve;creep;pile foundation;direct shear test;model test
日期:	2003-06-30
上传时间:	2009-09-18 17:07:32 (UTC+8)
出版者:	國立中央大學圖書館
摘要:	為瞭解軸向承載基樁於長期載重作用下之行為，本研究以室內模型試驗及粘彈理論之數值分析程式，探討土體的潛變行為對基樁於長期承載下之樁身與樁底承載力分配、荷載傳遞行為、以及樁體沉陷反應之影響。室內試驗以直剪儀對台北盆地粉質黏土及石門粉土進行樁–土界面之長期受剪潛變試驗，試驗結果顯示樁–土界面之剪動位移率將隨所受剪應力準位的增加而上升。隨著荷載作用時間的增加，剪動位移率與時間之關係於雙對數座標中呈近似線性遞減的趨勢，此遞減斜率與樁–土界面所受之覆土應力、應力準位大小無關。在相同應力準位情況下，不同性質土體之剪動位移率不同，但其位移率於雙對數座標中之遞減斜率相似。室內模型試驗及現地樁載重試驗結果均發現，在樁頂定荷載持續作用的情況下，樁頂位移有潛變現象，樁體確有將載重自淺層向深層傳遞的現象，使得樁體底部之承載呈現隨時間增加的趨勢。模型基樁試驗結果更顯示上部樁土界面摩擦力會隨時間減小，下部樁土界面之摩擦力會隨時間增加，使得摩擦力沿著樁身的分佈趨於均勻一致。而在數值分析部份，本研究以黏彈理論中之對應原理(correspondence principle)，透過黏彈塑性之t-z曲線，建立一套較簡化之軸向荷載基樁依時反應分析模式，可適用於多層土壤以及土體強度隨深度增加的情況。經與有限元素程式及模型試驗結果比對，此一簡化分析模式確能合理呈現軸向承載基樁於定荷載持續作用下之依時反應。 With a series of model tests and numerical analysis, pile behavior under sustained axial load are investigated to comprehend with the affections of soil creep on pile load distribution, load transfer and settlement. From the interface direct-shear test, it is revealed that the displacement rate is proportional to the stress level of the spacemen. As loading time elapsed, the logarithm of displacement rate decreases linearly with the logarithm of time. The slope of this relationship is essentially independent of the normal stress and stress level. Under identical stress level, different soil presents different displacement rate, but the relationships between the logarithm displacement rate and the logarithm of time are similar. From both in-situ and model pile tests, the incremental head settlement and tip load under sustained axial load are discovered, which shows that loading is transferred gradually from shallow to deeper layers. Furthermore, it is revealed from the model pile tests that skin friction decreases in the upper part and increases in the lower part of pile which forming a more uniform distribution of skin friction. With correspondence principle, a simplified time-dependent pile behavior analysis program is established utilizing viscoelastic–perfect plastic t–z curve. The situations of multiple layers and soil strength increasing with depth are taken into account in this program. Comparing with FEM program and pile test results, this program can rationally simulate the pile behavior under sustained axial load.
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