臺灣大學: 土木工程學研究所卿建業; 陳皆儒葉建儀Yeh, Jian-YiJian-YiYeh2013-04-012018-07-092013-04-012018-07-092010http://ntur.lib.ntu.edu.tw//handle/246246/255887大地工程中存在著許多不確定性(uncertainty)，以往傳統的設計中並沒有考慮到不確定性因子，而量化不確定性在可靠度設計中是一個重要的議題，其中剪力強度估算為土壤承載力的重要指標，而該如何利用現地調查的資料去預測剪力強度與有效的降低剪力強度之不確定性即是本研究的目的。本研究會有系統性的將當有許多資訊的情況下去預測剪力強度，並且利用貝氏分析(Bayesian analysis)的演算法，進而推導出在不同條件下所想要預估的剪力強度之事後機率分布(posterior PDF)，且該分布可求取剪力強度之期望值與標準偏差。其中無凝聚性土壤(cohesionless soil)剪力強度的代表即為尖峰狀態的有效應力摩擦角(effective friction angle,fp)。而本研究將探討影響摩擦角的因素有：相對密度(relative density, Dr)，平均粒徑(mean particle size,D50)、最大與最小孔隙比(maximum and minimum void ratio ,emax emin)、標準貫入試驗中的(N1)60值與圓錐貫入試驗的qc值。這些參數間彼此的關係(correlation)與該如何利用參數間的關係去作演算，以便往後在要求取土壤摩擦角的機率密度函數時，即可利用手邊的已知資料，帶入符合該條件下所推導出來的算式，去估算出欲知的摩擦角，當然已知的資訊愈多，所估出來的摩擦角也就愈準確，其不確定性也就愈小。 關鍵字：乾淨砂、不確定性、摩擦角、關聯性、貝式分析It is essential to characterize the uncertainties of soil shear strengths, including friction angles of sands, for geotechnical reliability-based design. In particular, it is of practical interest to reduce the uncertainties in friction angles based on all available information by correlation, given the considerable cost of a typical site investigation. Although it is relatively simple to reduce uncertainties by correlation when the information is one dimensional (or univariate), it is quite challenging to reduce uncertainties by using multivariate information through multiple correlations. This study proposes a systematic way of constructing multivariate correlations on friction angles of clean sands. A set of simplified equations are obtained through Bayesian analysis for the purpose of reducing uncertainties. The inputs to the equations are the results of field and laboratory tests, and the outputs are the updated mean values and standard deviations of the friction angles. Test databases are used to demonstrate the consistency of the proposed simplified equations. Results show that uncertainties in friction angles can be effectively reduced by incorporating multivariate information. Given that reliability-based design can justify more economical design with reduced uncertainties, the proposed equations essentially link the value of more and/or better tests directly to final design savings.2684761 bytesapplication/pdfen-US純砂不確定性摩擦角關聯性貝式分析clean sandsuncertaintyfriction anglecorrelationBayesian analysisthesishttp://ntur.lib.ntu.edu.tw/bitstream/246246/255887/1/ntu-99-R97521120-1.pdf