砂土中模型基樁之單向反覆軸向載重試驗;Cyclic Axial Loading Tests on Model Pile in Sand

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Title:	砂土中模型基樁之單向反覆軸向載重試驗;Cyclic Axial Loading Tests on Model Pile in Sand
Authors:	陳思凱;Chen, Ssu-Kai
Contributors:	土木工程學系
Keywords:	離岸風力發電;模型樁試驗;反覆軸向作用;乾砂;offshore wind power;model pile;cyclic axial load;dry sand
Date:	2017-01-24
Issue Date:	2017-05-05 17:06:41 (UTC+8)
Publisher:	國立中央大學
Abstract:	多樁形式的離岸風機基礎需長期承受上部結構重量及週期性作用力。當上部結構受到風力、洋流及波浪等週期性側向作用力傳遞至下部結構，對樁基礎產生週期性的軸向壓力及拉力，造成樁基礎產生差異沉陷使風機傾斜，進而影響風機系統運轉之穩定性。因此，本研究主要目的為探討基樁受長期反覆軸向作用力下之受力行為。本研究利用空氣霣降法製作Dr=60%乾砂試體，進行1-g模型樁載重試驗。模擬風機基礎於自重條件安全係數為3的情況下，再施加反覆軸向載重振幅進行試驗。本研究進行靜態試驗時，發現靠近樁底砂土相對密度明顯影響樁底承載力的發揮，故極限靜壓載重試驗總共進行10組，並記錄砂土各層相對密度，以便觀察對樁底承載力之影響，確保日後試驗砂土條件之一致性。單向反覆載重試驗總共進行6組，3組受反覆軸向壓力、3組受反覆軸向拉力，反覆荷載分別為1/3Pu、1/6Pu及1/12Pu，反覆作用週數分別為10000、10000及20000次。　　試驗結果顯示，較大的反覆軸向振幅下，樁頭勁度隨著反覆作用次數衰減越明顯，樁頭位移遞增率亦越大。相同反覆軸向振幅下，樁基礎受反覆軸向壓力的殘餘位移較大。當反覆作用週數增加時，樁身摩擦力逐漸減小，但樁底承載力則逐漸增大。 ;Because the offshore wind turbine pile foundations such as that jacket and tripod are subjected to the WTG loading and long-term wind and wave loading transmitted from upper structure to lower substructure, the generated cyclic axial compression and tension, result in pile groups of difference settlement, affecting the stability of operation of the wind turbine. Therefore to investigate different pile behavior under cyclic axial load, is the destination of this study. 　　In this study, air pluviation method of sample was adopted to prepare a dense homogeneous dry sand specimen with a relative density of 60%, and 1-g model pile load test was conducted. When conducting axial cyclic load test, the loading which approach 1/3 of ultimate static in the axial load capacity was applied to simulate the normal conditions under safety factor of 3.In the static load tests it was, found that near bottom of the pile the sand relative density significantly affects the pile bearing capacity, the ultimate static load test total was totally 10 groups, with recording the relative density of sand layers in order to observe the variation of pile bearing capacity, and to ensure the consistent in preparation of sand samples in the future. Six unidirectional cyclic axial load test were conducted, in which three tests were under cyclic axial compression, and three tests under cyclic axial tension. The magnitude of loading were 1/3Pu, 1/6Pu and 1/12Pu, and the number of cycles were 10000, 10000 and 20000 respectively. 　　The results represent that the larger number of axial load cycles apply, the smaller equivalent stiffness of pile head was obtained as well as pile head displacement increases with an increasing number of cycles. Under the same condition of axial load cycles, the accumulated residual displacement of pile foundation under cyclic axial compression was larger than cyclic axial tension case. When increasing number of cycles, the pile shaft friction decreases. But the bearing capacity of pile tip increases.
Appears in Collections:	[Graduate Institute of Civil Engineering] Electronic Thesis & Dissertation

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