摘要
自升式平台船為離岸風機設置普遍使用的大型船機具，透過支撐基腳站立於海床，平台船身將抬升超過海平面，避免波浪侵襲，增加施工穩定性與作業時間。由於自升式平台船站立於極疏鬆砂土時可能發生基腳貫穿剪力破壞，造成貫入深度較大致使海事施工作業時間拉長甚至自升式平台船毀損，亦或是站立於緊密砂土時可能產生一般剪力破壞隆起影響周遭結構物穩定性，為避免上述問題需在自升式平台船施工前進行承載力與影響範圍評估。但現有規範如SNAME(2008)僅以淺基礎承載力公式評估支撐基腳貫入海床土壤承載力與深度，因此本研究以有限元素模型分析支撐基腳貫入與提腿期間周遭海床土壤行為，並搭配Coupled Eulerian-Lagrangian method解決支撐基腳貫入時土壤大變形(Large deformation)問題。
本研究首先將數值模型貫入深度與承載力計算成果與模型試驗成果比較進行模型驗證，顯示貫入緊密程度較高砂土成果與模型試驗較為吻合，且SNAME(2008)建議之計算方式明顯低估緊密程度疏鬆以上之砂土承載力。接著針對不同支撐基腳尺寸部分進行參數分析，本研究模型成果顯示支撐基腳承載力、地形影響範圍、土體性質影響範圍皆與支撐基腳直徑呈現正相關。本研究另參考先導型離岸風場場址鑽孔資料選定模型土壤參數，分析貫入不同緊密程度砂土及提腿造成之地形、水平應力、土體性質影響範圍，緊密程度較高之砂土明顯有較大之地形、土體性質影響範圍。
最後本研究以彰濱風場土壤條件以及台灣現有自升式平台船進行案例分析，說明較大尺寸之支撐基腳達預壓載重時貫入深度較淺，足以提供自升式平台船更多施工彈性，而較小尺寸支撐基腳與無基腳支撐腿則會造成較小地形變化影響區域，但無基腳支撐腿可能產生較大之土壤性質改變區域。

SUMMARY
Spudcan for offshore mobile drilling rigs are large saucer-shaped foundations that can penetrate into the seabed to stabilize the rig in position. However, the current guideline such as SNAME (2008) only assess bearing capacity and penetration depth by shallow foundation bearing capacity formula, so this study establish the finite element model to analyze the seabed soil behavior during spudcan penetration and extraction ,also solve the problem of large deformation when the spudcan penetration by using Coupled Eulerian-Lagrangian method.
In this study, spudcan bearing capacity calculated by numerical model is compared with the results of the model test for the numerical model verification, it shows that numerical model and model test match more well when sand is more dense, besides model verification illustrate that the shallow foundation bearing capacity formula suggested by SNAME(2008) underestimate the bearing capacity. After model verification, parameter study of different size spudcan shows that the bearing capacity of the spudcan, the influence range of the terrain, and the influence of the soil properties are positively correlated with the diameter of the spudcan. In this study, the soil parameters of model are obtained by referring to the drilling data of the Taiwan pilot offshore wind farm, and input these soil parameters from different relative density sand to numerical model then access the bearing capacity of the spudcan, the influence range of the terrain, and the influence of the soil properties. From the parameter study of relative density sand, it shows that sandy soil with a higher degree of relative density has a greater range of terrain effects.

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