| 摘要: | 臺灣位於歐亞板塊交界，地震頻繁發生，且臺灣總面積約有三分之一為平原地區多屬地質軟弱的沖積地層，地下水位面高，土壤液化潛能較高，當大規模地震作用時，即可能發生土壤液化。板樁牆具有優秀的經濟性、便利性及施工性，因此常被作為河床、港灣、碼頭的擋土系統。河床地盤的土壤多為沖積土，又河床地區的地下水位面非常高，因此該區域通常有較高土壤液化潛能。當土壤液化發生時，板樁牆會因土壤大變形而傾倒及損毀。真實地震的頻率含量分佈皆不同，不同頻率含量的振動會使牆-土系統有不同的反應。本研究藉由四組動態離心模型試驗，模擬建於可液化地盤之板樁牆受不同頻率振動時的反應行為。在24 g離心重力場中，四組試驗輸入基盤最大加速度為0.16 g、0.15 g、0.27 g、0.08 g，頻率含量包含1 Hz、1 Hz與3 Hz合成的非等振幅正弦波，四組試驗配置及其他試驗條件均相同，並透過線性可變差動變壓器(Linear Variable Differential Transformer, LVDT)與地表追蹤計記錄板樁牆及土層表面受振的橫向位移行為。
試驗結果顯示在相同基盤加速度情況下：受3 Hz含量較多的基盤振動，土層具有較高超額孔隙水壓激發量、較大板樁牆傾斜位移及較大地表土壤位移量。板樁牆兩翼板的旋轉角分別為4.61°與4.15°，於背填土區距離板樁牆1.38 m處，土壤平均位移量為0.25 m；受3 Hz含量較低的基盤振動，會引致小超額孔隙水壓激發量、板樁牆傾斜位移、地表土壤位移與沉陷，板樁牆兩翼板的旋轉角分別為2.54°與3.26°；於背填土區距離板樁牆中心1.38 m處，土壤平均位移量約為0.18 m。
;The plain of west Taiwan is formed of soft alluvium ground with a high groundwater level. As Taiwan is located on the Circum-Pacific Seismic Belt, earthquakes occur frequently and can lead to soil liquefaction on the alluvium ground. Sheet pile walls are often used as a retaining system at riverbanks, harbors, and piers due to their cost-effectiveness, convenience, and constructability. Near the river, soil deposits are composed of alluvial soils and groundwater levels are very high, therefore soil liquefaction are usually more common around this area. When soil liquefaction occurs, the sheet pile walls would fall or become damaged as a result of soil deformation. The frequency content distribution for each earthquake is varied under real conditions; earthquake shaking at different frequency contents will provoke different behaviours from the wall-soil system. In this study, four dynamic centrifuge tests were conducted to simulate the sheet pile wall constructed at liquefiable ground, subject to the base shaking at different frequency contents. The peak base acceleration of input motion for each test were 0.16 g, 0.15 g, 0.27 g and 0.08 g, with frequency contents of 1 Hz and 1+3Hz, 21 cycles of non-equal amplitude sinusoidal wave. The horizontal displacement of the sheet pile wall and ground surface induced by shaking were measured and tracked by the Linear Variable Differential Transformers (LVDTs) and surface markers.
The results revealed that in the same peak base acceleration, models subjected to an input motion with higher 3 Hz content has higher excess pore water pressure excitation, and larger pile lateral displacement, the rotation angles of the two wing plates of the sheet pile wall were 2.54° and 3.26° respectively, and the average ground surface movement towards the dredge area was 0.25 m. Models subjected to an input motion with lower 3 Hz content has lower excess pore water pressure excitation and excitation rate, and lower pile lateral displacement; the rotation angles of the two wing plates of the sheet pile wall were 2.54° and 3.26° respectively, and the average ground surface movement towards the dredge area was 0.18 m. |
