土壤液化引致側向滑移對樁基礎之影響及其對策;Liquefaction-induced lateral spreading and its effect and mitigation on pile foundations

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Title:	土壤液化引致側向滑移對樁基礎之影響及其對策;Liquefaction-induced lateral spreading and its effect and mitigation on pile foundations
Authors:	翁崇期;Weng, Chung-Chi
Contributors:	土木工程學系
Keywords:	傾斜地盤;液化引致側向滑移;離心模型試驗;樁基礎;inclined ground;lateral spreading;centrifuge tests;pile foundations
Date:	2018-02-09
Issue Date:	2018-04-13 10:47:39 (UTC+8)
Publisher:	國立中央大學
Abstract:	傾斜的緩坡地層若為具液化潛能的疏鬆砂，地震發生時便容易液化造成側向滑移現象，若能更加瞭解側向滑移對緩坡地層中樁基礎所造成之影響，將有助於評估在可能液化地盤之結構物樁基礎的耐震能力，同時也可減少地震引致之土壤液化災害，並提升基礎耐震設計之合理性與經濟性，因此在土壤液化引致側向滑移情況下樁基礎之行為，有進行研究之必要性。在深度為12.5 m 的砂土地盤，透過輸入1Hz、15 次振動(cycles)的非等振幅類正弦波(Hanning-window)作為主要振動事件，樁基礎樁徑為0.48 m，樁心距為1.2 m，並以鉸接之方式固定於箱底這些條件下所得到之研究成果，可以得出以下結論:(1)在樁頭容許變位為15 mm 下，於純砂層地盤中，單樁基礎最大樁頭側向位移量與土壤反力，和群樁基礎相差不大。單樁基礎最大樁身彎矩高於群樁基礎。於上覆非液化土層地盤中，單樁基礎最大樁頭側向位移量與群樁基礎最大位移量相差不大，單樁基礎最大樁身彎矩高於群樁基礎，而土壤反力方面，單樁基礎最大土壤反力高於群樁基礎最大土壤反力。(2)主要振動事件中，群樁基礎之最大彎矩、最大土壤反力皆大於單樁基礎，造成此現象之原因，推測是群樁基礎表層樁土相對位移量高於單樁基礎所導致之結果。(3)比較G-type 試驗中之樁頭位移量、最大彎矩量、最大軸力與土壤反力等試驗結果，最大樁頭位移量、最大樁身彎矩量、最大軸力與土壤反力大小依次均為上覆非液化土壤層傾斜地盤，其次為傾斜純砂層地盤，最後則為水平上覆非液化土壤層地盤。(4)試驗GSP-P-T 孔隙水壓消散時間較試驗G-P-T 長，試驗GSP-P-T 所承受之彎矩量、樁身軸力與土壤反力，皆高於試驗G-P-T。而試驗GSP-P-T 樁頭位移量與土壤側向位移量，低於試驗G-P-T。;The wide extent of liquefaction-induced lateral flow is a major cause of damage to civil structures. When the pile foundations behavior affected by lateral spreading is well understood, the seismic design and improvement treatments could be applied to such structures. It is necessary to know the pile behavior in sandy ground subjected to lateral spreading. In this study, the bottom of model piles were hinge connections and the diameters of the piles is 0.48 m. The distance between each pile is 1.2 m. Under the main event of 0.2 g and 15 cycles base input motion, some conclusions can be shown below: (1) Within the allowable lateral displacement 15 mm, the lateral pile displacement and maximum soil reaction is similar in single pile and group piles in pure sand deposit ground. Maximum pile moment of single pile will be higher than that in group piles. In sand deposit ground with one non-liquefied soil layer, the lateral pile displacement is much similar in single pile and group piles. Maximum pile moment and maximum soil reaction of single pile will be higher than group piles. (2) After the main-shaking event, the maximum moment and soil reaction in group piles are higher than those in single pile. (3) In G-type tests, all the order of maximum lateral pile displacement, maximum pile moment, maximum axis froce and maximum soil reaction are test G-M-T > test G-P-T > test G-M-H. (4) The dissipation time of excess pore water pressure in test GS-P-T is longer than test G-P-T, all the maximum pile moment, maximum axis force and maximum soil reaction in test GS-P-T are higher than those in test G-P-T. However, the maximum lateral pile displacement and soil displacement in test GS-P-T are smaller than those in test G-P-T.
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