根據研究指出台北粘土於小應變階段具有高勁度之行為，且其不排水勁度具有劣化行為，即勁度隨著應變增加而減少。因此在程式分析部分需考慮粘土之高初始勁度與劣化行為。由於現今之分析雖有考慮到小應變下之高勁度行為與軸向加壓試驗的劣化行為，但實際工程進行時不同位置之粘土受載方式不同，其分析上更應考慮不同應力路徑下之劣化行為。因此，本研究針對台北重模粘土進行三軸 壓密不排水於不同應力路徑下之解壓再壓試驗，並同時施作彎曲元件試驗。試驗結果顯示對於所選用的土壤，單以應變來看AC與LE其解壓再壓彈性模數與初始彈性模數之比值具有單一的劣化行為，並可迴歸得到單一劣化曲線。但若以應力水平來看，因受破壞應變影響則不同應力路徑之劣化行為會不同。

Behaviors of high initial Young’s modulus and stiffness degradation were observed on Taipei silty clay, and were applied to the numerical analysis in excavations with advanced soil models. The analysis with consideration of high initial Young’s modulus and stiffness degradation under axial compression condition yields in better prediction results. However, stress paths in a real excavation are different for soil elements at different positions. Thus, the degradation behavior of stiffness for soils under different stress paths should be investigated. This study presented a series of CK0U (K0 consolidation and undrained shearing) unloading-reloading triaxial tests under three stress paths, i.e. AC (axial compression), AE (axial extension), and LC (lateral extension), with bender element tests. Test results demonstrated that both secant Young’s moduli and shear moduli degraded with the increase of strain and stress level. From results of AC and LE tests, stiffness degradation ratios for tested soil versus axial strains are unique (or stress path independent). Nevertheless, the degradation ratio versus the stress level is affected by the failure strain and dependent on stress paths.

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