- 學位論文
極限狀態的土壤抗剪強度的特徵值
Characteristic Values of Soil Shear Strength for Ultimate Limit States
摘要
歐洲規範7 (Eurocode 7) 將土壤參數的特徵值定義為“對影響極限狀態發生的值的謹慎估計”。當前的研究著眼於在存在空間變異性的情況下、決定剪力強度的特徵值。驅動的剪力強度（即影響極限極限發生的剪力強度）不僅受到沿潛在滑動面的空間平均的影響，而且還受到尋找弱帶的影響。前者（空間平均）減小了驅動剪力強度的變異性，後者（弱帶搜索）減小了驅動剪力強度的期望值。前人文獻中提出了幾個簡單的公式、以決定剪力強度的特徵值，但他們大多只考慮空間平均，而忽略了弱帶搜索，這可能是不保守的。當前的研究採用最弱路徑模型（WPM），WPM雖是一個簡單的模型，卻同時考慮空間平均和弱帶搜索二個因素、以模擬驅動的剪力強度。由於WPM需要校準，因此當前的研究使用隨機有限元方法（RFEM）來針對一些土壤力學與基礎工程問題對WPM進行校準，校準的WPM的行為與RFEM的行為相似。基於校準的WPM，當前的研究提出了一個簡化公式來決定剪力強度的特徵值，並在實際案例中、驗證該公式的有效性。驗證結果發現，對於不確定性受空間變異性支配、且破壞面受中、低度約束的問題，所提出的公式與文獻中現有的簡化公式相比、具有顯著改進。
並列摘要
Eurocode 7 defines the characteristic value of a soil parameter as “a cautious estimate of the value affecting the occurrence of the limit state”. The current study addresses the determination of the characteristic value of shear strength in the presence of spatial variability in the context of the ultimate limit state. The mobilized shear strength, the shear strength affecting the occurrence of the ultimate limit state, is influenced not only by the spatial averaging along the potential slip curve but also by seeking out mechanically admissible weak zones. The former factor (spatial averaging) reduces the variance of the mobilized shear strength, whereas the latter factor (weak-zone seeking) reduces the mean of the mobilized shear strength among others. Several simple formulas have been proposed in the literature for the determination of the characteristic value of shear strength. However, they mostly consider spatial averaging only and ignore the weak-zone seeking, which is potentially unconservative. The current study adopts the weakest-path model (WPM). The WPM is a simple model that can simulate the mobilized shear strength considering both factors of spatial averaging and weak-zone seeking. Since the WPM requires calibration, the current study calibrates the WPM for several geotechnical problems using the random finite element method (RFEM). The behaviors for the calibrated WPM are found to be similar to those for the RFEM. Based on the calibrated WPM, a simplified formula is proposed to determine a mobilization-based characteristic value. The effectiveness of this formula is showcased by real case studies. It is found that for problems whose uncertainty is dominated by spatial variability and whose slip curve is not highly constrained by mechanical admissibility, the proposed formula provides significant improvements over existing simplified formulas in the literature.