軟弱黏土模型基樁側向疲勞載重試驗

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题名:	軟弱黏土模型基樁側向疲勞載重試驗
作者:	吳羿慶;Wu, Yi-Ching
贡献者:	土木工程學系
关键词:	黏土;模型基樁
日期:	2019-11-11
上传时间:	2020-01-07 14:21:34 (UTC+8)
出版者:	國立中央大學
摘要:	離岸風機之單樁基礎在海上受風力、波浪力及地震力等反覆水平側向力之作用。黏土與砂土層受到波浪力作用時，因為環境的不同導致單樁基礎的長期受力行為出現較大的差異。本研究利用模型樁模擬單樁基礎於海上受波浪力作用下基樁之行為。本研究以曾文水庫之黏土進行大型壓密來製作重模試體，利用模型樁進行靜態極限側向加載試驗，將試驗實測之結果加以迴歸分析求取樁身反應。再以不同應力準位之單向反覆加載試驗，觀察樁頭受力之累積殘餘位移、累積殘餘旋轉角或割線勁度等之趨勢，並透過求取樁身彎矩、土壤反力或樁身位移等，研究其樁-土互制行為。由試驗結果可知，在靜態極限側向加載試驗中最大彎矩隨側向載重增加而增加，且樁身發生最大彎矩之深度也隨載重增加而逐漸下移。在側向反覆加載試驗中，等效勁度隨著應力準位增加而變小，應力準位越大等效勁度越快趨於平緩。最大彎矩隨著作用週數增加而增加，樁身最大彎矩之深度也隨著作用周數增加而逐漸下移。單向反覆側向加載試驗之最大彎矩比靜態極限加載試驗之成果大20-30%，最大彎矩深度則增加25-30%。側向加載使得間隙產生時，因為土壤軟化之影響，會造成樁身旋轉角超過DNV之安全之範圍，等效勁度也會下降至初始等效勁度之27%，使其安全性受到影響。 ;In general, the monopole of offshore wind turbine is subjected to wind load, wave load, earthquake and other repetitive lateral forces. Comparing with sand, clay typically has different geological and environmental conditions due to the existing of soft clay in the upper layer and the daily tide movement, which may lead to the considerable difference in long-term behavior of monopile. The test specimens are prepared by remolding the silty soils from Zengwun Reservoir. The loading tests are carried out with the model pile. The test results are further analyzed to obtain pile responses by using regression analysis. The cyclic lateral loading test was applied with different stress levels to observe the trend of permanent displacement, permanent rotation angle and pile secant stiffness. Using the calculation of pile bending moment, soil reaction force or pile displacement to understanding the behavior of pile-soil interaction. The results of the test indicated that the value of maximum moment increased when the lateral loading increased, and the depth which the maximum moment occurred is also deeper in ultimate lateral loading test. The equivalent stiffness becomes smaller as the stress level increases. The greater the stress level, the faster the equivalent stiffness tends to be gentle. The value of maximum moment increased when the lateral loading increased, and the depth which the maximum moment occurred is also deeper in cyclic lateral loading test. The greater the increase in the bending moment as the stress level becomes larger. When lateral loading causes the gap to be generated, it will cause partial cohesion and soil softening between the pile and the soil. This effect will cause the permanent rotation angle to exceed the safe range defined by DNV, which will affect the safety of offshore wind turbine.
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