工學院: 土木工程學研究所指導教授: 卿建業宋上平Sung, Shang-PingShang-PingSung2017-03-132018-07-092017-03-132018-07-092016http://ntur.lib.ntu.edu.tw//handle/246246/277959本研究探討黏土不排水剪力強度的空間變異性(spatial variability)對開挖底面隆起穩定(basal-heave stability)安全係數的影響。研究發現傳統穩定性分析中假設固定破壞面的分析方式無法有效表現出臨界關聯性長度(critical SOF)現象。因此隨機有限元素模型(RFEM)被用來分析開挖底面隆起穩定安全係數(FSFEM)，並且與傳統開挖底面隆起分析方法–圓弧滑動模型(slip circle model, SCM)做比較，藉此闡述critical SOF現象與成因。研究結果顯示，在某些「糟糕的」關聯性長度(scale of fluctuation, SOF)下，FSFEM的平均值會明顯低於定值性(deterministic)分析下的標稱(nominal)安全係數(FSn)。由於固定破壞面的SCM無法掌握臨界破壞面尋找最弱滑動面的趨勢，分析結果也顯示出SCM無法完全表現出critical SOF現象。本研究提出一個基於SCM的機率模型–最弱連結模型(weakest link model)，並且在此模型中允許臨界破壞面在數個潛在滑動面中尋找最弱的潛在滑動面。以此方式有效掌握RFEM分析結果與量化critical SOF現象，並且不需要透過額外的RFEM分析即可達成。最後以一張可靠度分析圖表比較在具有相同FSn的情況下，基於最弱連結模型的破壞機率與基於SCM的破壞機率。由於SCM無法表現critical SOF現象，因此SCM破壞機率明顯小於最弱連結模型表現出的破壞機率。SCM在可靠度分析的架構下偏向不保守。This study explores the basal heave stability of excavations in spatially variable clays. It is shown that traditional stability analysis methods based on assumed prescribed slip curves cannot capture the phenomenon of a critical SOF. Therefore, Random finite element method (RFEM) is adopted to simulate the basal heave factor of safety (FSFEM). In order to figure out the phenomenon of a critical SOF, FSFEM will be compared to the factor of safety estimated by slip circle method (SCM). It is evident that the mean value of FSFEM is significantly less than its nominal value at some worst-case SOF. It is also shown that owing to an assumed prescribed slip curve of SCM, SCM is not allowed to seek for the weakest slip curve. In this study, a “weakest link” model which is based on SCM is proposed. However the model is allowed the critical slip curve to seek for the weakest potential slip curve among potential slip curves. The weakest link model is able to capture the phenomenon of a critical SOF, both qualitatively and quantitatively.4576248 bytesapplication/pdf論文公開時間: 2017/8/2論文使用權限: 同意有償授權(權利金給回饋學校)臨界關聯性長度空間變異性可靠度設計深開挖開挖底面隆起critical scale of fluctuationreliability-based designspatial variabilitybasal heavedeep excavationthesis10.6342/NTU201601428http://ntur.lib.ntu.edu.tw/bitstream/246246/277959/1/ntu-105-R03521124-1.pdf