Updating Uncertainties in Friction Angles of Clean Sands

Abstract

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 update the uncertainties in friction angles on the basis of all available information by correlation, given the considerable cost of a typical site investigation. Although it is relatively simple to update uncertainties by correlation when the information is one dimensional (1D) or univariate, it is quite challenging to update uncertainties by using multivariate information through multiple correlations. This study proposes a systematic way of constructing multivariate correlations on friction angles of reconstituted clean sands. A set of simplified equations are obtained through Bayesian analysis for the purpose of updating 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 updated uncertainties, the proposed equations essentially link the value of more and/or better tests directly to final design savings.