自升式平台船基礎於砂土 (上層)-黏土 (下層) 土層之崩潰荷重評估

Abstract

摘要 台灣預計於2025年前完成5.5 GW的離岸風力發電裝置容量。離岸工程中自升式平台船被廣泛使用，而離岸工程所採用的基礎尺寸通常大於陸域工程所使用的基礎。隨著基礎尺寸的增加，基礎受外力作用時所影響的土壤範圍亦將擴大，故進行大型基礎的承載力分析過程中考量互層土壤效應是必須的。本文考量條型基礎於砂土 (上層) – 黏土 (下層) 互層土壤時的極限承載力分析並利用 Meyerhof (1974) 的分析模型與SNAME (2008) 所建議的土壤參數近似式進行分析與討論。結果顯示，對於基礎尺寸較大或上土層的內摩擦角較大的情況，基礎整體承載力將受下土層強度與砂土層厚度影響。此外，若僅考量上土層發生全面剪力破壞所得之承載力可能是被高估的，故進行基礎承載力評估時考量互層土壤效應是必須的。

Abstract The target, offshore wind farm constructions in Taiwan, 5.5 GW capacity is expected to be completed by 2025. In the field of offshore engineering, jack-up barges are widely applied and the dimensions of offshore foundations are usually larger than those of onshore footings. As the dimensions of foundations increase, the affected depth range of the footing with plastic collapse load subjected may extend to the subsequent soil deposit, and hence it is necessary to consider the effect of layered soils in the bearing capacity evaluation of foundations. This study applies the analysis model purposed by Meyerhof (1974) and the approximate coefficient formula suggested by SNAME (2008) to assess the bearing capacity of the strip foundation on sand overlying clay soils. Furthermore, the result indicates that the bearing capacity of footings would be affected by the strength of the bottom clay layer and the thickness of the upper sand layer, especially for the magnitude of the friction angle of the sand layer becoming large or the foundation embedded in a stronger soil with short distance from the footing base to a following weaker soil layer. In summary, the bearing capacity determined by general shear failure in the top layer might be overestimated, so it is of particular necessary to consider the soil strata effect on bearing capacity assessment.