由於日本福島311核能災害的事件發生，我國政府於100年宣布國家新能源政策，「確保核安、穩建減核；打造綠能低碳環境；逐步邁向非核家園」，其中以離岸風力發電作為綠能的重點開發項目。我國離岸風場開發勢在必行，然而目前我國尚未完成本土化之離岸風機設計規範建立，進行離岸風機基礎設計時，各風場開商主要依循國際離岸風電先進國家之設計規範。以德國規範為例，為滿足BSH (2008)建議離岸風機基礎設計時需結合動態土壤力學試驗成果之要求，Kuo (2008)提出土壤勁度衰減模型，以無凝聚性土壤受反覆作用力下之應變量及割線模數結合樁土互制有限元素模型，計算基樁受長期反覆側向作用力下之樁身變形。
土壤勁度衰減模型中包含兩個勁度衰減參數，主要透過動態三軸剪力試驗求得，然而勁度衰減模型的土壤應變計算式為計算永久變形量，故忽略反覆作用時土壤回彈應變的影響。然而本研究以標準砂進行五組不同應力條件之動態三軸剪力排水試驗，加載條件皆以週期10秒反覆作用10000次之反覆應力(模擬環境載重)，分析無凝聚性土壤於排水條件下受反覆載重時的軸向變形反應，其中土壤軸向變形包含塑性應變及回彈應變，且分析無凝聚性土壤受反覆作用力之軸向塑性應變及軸向回彈應變，並提出回彈應變與作用次數的預測式，取得動態土壤地工參數(勁度模數、回彈模數)，以期更新BSH (2008) 建議之勁度衰減模型，合理估算無凝聚性土壤受反覆應力作用下之永久應變量。

Stiffness Degradation Model (SDM) is proposed by Kuo (2008), SDM is one of method to calculate the permanent deformation responses of offshore wind turbine foundation and is suggested by the BSH standard “Design of Offshore Wind Turbines”.SDM contains two stiffness degradation parameters, which obtained by cyclic triaxial shear test. However, the soil plastic axial strain calculation formula of the stiffness degradation model is to calculate the permanent deformation, so the soil resilient strain has ignored under one-way cyclic loading. In this study, five sets of cyclic triaxial shear drainage tests under different stress conditions with Ottawa sand. The loading conditions were repeated with 10,000 times of cyclic load (simulated environmental load) in 10 seconds per cyclic.To analyze the axial strain of cohesionless soil under drainage conditions and axial strain of the soil under cyclic load included plastic strain and resilient strain. This study proposes a formula for the resilient strain to obtain dynamic soil parameters (stiffness modulus and resilient modulus), and expects to update the stiffness degradation model recommended by the BSH (2008). It is reasonable to estimate the permanent strain under the one-way cyclic stress of cohesionless soil.

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