本研究利用1-g縮尺物理模型振動台試驗，藉此探討群樁基礎於地盤發生液化時之受震反應特性，其為成功大學土木系與國家地震工程研究中心合作之套筒式基礎離岸風機縮尺模型試驗計畫之先導試驗。試驗使用新型雙軸向層狀剪力盒製作飽和砂土地盤試體，群樁模型之縮尺比例為1/25，採2x2矩形排列方式，基樁採用外徑81 mm及長度2m的鋁合金管模型設計之相似律主要基於樁-土互制行為來決定。採用頻率2Hz之正弦波形來做為輸入運動，進行單向簡諧激振試驗；分別使用由小到大為30gal、50gal、75gal之加速度振幅，以達到不同程度之受震反應與液化情況。根據超額孔隙水壓激發情況，顯示振幅為50gal時，土體一半深度已達到部分液化；在振幅為75gal時，土體幾乎完全液化。液化發生後，代表地盤受震反應之土體與剪力盒框架加速度明顯下降，且框架產生高頻反應，並與土體出現明顯的相角差。進一步以一維剪力梁模式計算地盤受震時之剪應力與剪應變，由土壤應力-應變遲滯圈變化情況，顯示液化後之土壤弱化現象，據以討論剪力模數-剪應變-超額孔隙水壓之間關係，並利用群樁與風機模型前後兩次50 gal振幅試驗探討重複液化現象。群樁受震反應在液化前與地盤大致同步，液化後其加速度出現高頻振動，且與地盤間出現明顯相角差；樁身撓曲應變與彎矩在液化前逐漸上升，液化後則大幅降低。從以上試驗結果，可呈現出液化過程中土壤力學性質與樁-土互制行為之變化，能夠有助於掌握液化地盤中樁基礎之耐震性能。

To investigate the seismic response of a pile group during soil liquefaction, shaking table tests on a 1/25 scale model of a 2×2 pile group were conducted, which were pilot tests of a test project of a scale-model offshore wind turbine with jacket foundation. The pile group model comprising four slender aluminum piles with their pile heads connected by a rigid frame was designed with similitude considerations focusing on soil-pile interaction. The input motions were 2 Hz sinusoids with various acceleration amplitude. The excess pore water pressure generation indicated that the upper half of the ground specimen reached initial liquefaction under the 50-gal amplitude excitation, while in the 75-gal amplitude test almost entire ground was liquefied. After liquefaction, the soil and the movable-frame accelerations that represented the ground response considerably reduced, while both the movable frames and the piles exhibited high frequency jitters other than 2-Hz sinusoid, and meantime remarkable phase difference between the responses of the pile group and the ground was observed. Axial strains along the pile implied its double-curvature bending behavior, and the accordingly calculated moment declined significantly after liquefaction. These observations demonstrated the interaction between soil and piles during liquefaction. In addition, 1-D shear beam idealization was further introduced to deduce the stress-strain relationship of soil based on seismic ground response. Thus, the variation of mechanical properties of saturated sand with respect to the development of shear strain and excess pore water pressure were examined. The repeated liquefaction was also investigated using two of the excitation tests using the same input motion.

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