離岸風機單樁基礎(Mono-pile) 因其上部結構會受到多循環側向載重，例如風力、洋流、大浪等週期性水平力，並傳遞至風機基礎，可能會因土壤之水平承載力不足，造成過大的永久位移，或者是在樁身之勁度不足情況下，上部水平荷重產生之彎曲應力造成樁身的破壞，進而影響風機系統運轉之穩定性。因此，如何評估離岸風機基礎的水平極限承載力，以及在多循環的上部水平力作用下，預估單樁基礎的傾斜與水平位移，是本研究的主要目標。 本研究將現地樁基礎進行離心縮尺，於80 g離心重力場下，進行單樁基礎受反覆側向水平力之離心模型試驗共8組，其側推的高程皆位於地表上34 m處。A系列試驗條件為5組不同水位高度下，於上部結構施以相同反覆水平力；B系列試驗於乾砂試體施加不同大小之單向反覆水平力共3組，藉以觀察受反覆水平力下的單樁之位移、旋轉角、樁身彎矩沿深度的分布狀態，並討論不同循環數與水平力大小對單樁基礎的影響。試驗結果顯示：(1) 在不同水位高程情況下，砂試體及單樁的自然頻率皆大致相同；(2) 以最大水平承載力試驗中，樁身最大彎矩發生位置隨力量增加而往淺層發展，在1383 kN側推力作用下，最大彎矩位於地表下深度1.6 m (d/Dp =0.76)處；(3) 在230 kN之多循環水平力側推情況下，海床面11.2 m (d/Dp =5) 以下的樁基礎幾乎沒有彎矩；(4) 在相同的多循環水平力下，隨著循環數的增加，殘餘變位、旋轉角、樁身彎矩而增加，但其增量越發趨緩，且樁頭割線模數提高。 ;The mono-pile supported offshore wind turbine usually subjected to cyclic lateral loadings induced by wind, ocean current, sea wave etc. It would cause the shear failure of surrounding soil for rigid pile foundation or the plastic yield of pile by bending moment, leading to the instability of wind turbine system. Therefore, it is very important to estimate the ultimate lateral bearing capacity of monopole foundation, and to predict the inclination and permanent horizontal displacement of pile under cyclic lateral loadings. In this study, 8 models were conducted in 80 g acceleration field by using the NCU geotechnical centrifuge and rigid container. The lateral load for each test was applied at the elevation of 34 m above the ground surface. A-series tests were designed to have different water level and subjected to the same cyclic loadings. B-series tests were dry sand models and the different amplitude of cyclic lateral loadings were applied to the mono-pile. From the test results, the following conclusions can be drawn. (1) The natural frequencies of mono-pile and sand bed did not change with different water level. (2) The maximum bending moment occurred at the depth of 1.6 m under the ground surface while the lateral load was 1383 kN. The place of maximum bending moment would move upward along the pile with increasing lateral loads. (3) When the maximum cyclic lateral loading is 230 kN, the bending moment of pile is almost zero under the ground surface of 11.2 m, which is about 5 times of pile diameter. (4) Under the same amplitude of cyclic lateral loadings, the increase of cycles leads to the increasing of permanent lateral displacement, rotation angle and bending moment of pile, but the increments decrease with more number of cycles.
