This paper discusses ways to quantify uncertainties in soil shear strengths by using site investigation results. The main challenge lies in the fact that the information obtained in site investigation, CPT value, may not be the design parameters themselves but are only correlated to the design parameters. Above all, there is a challenge in combining information: how to quantify the uncertainties when there are multiple sources of information? In this paper we will address the aforementioned challenges and propose a probabilistic framework to handle these difficulties. The design parameters of interest include undrained shear strength of clays and friction angles of sands. Sets of simplified equations will be obtained through the probabilistic analysis for the purpose of quantifying uncertainties: the inputs to the equations are the results of in-situ or laboratory tests and the outputs are the updated mean values and coefficients of variation (c. o. v.) of the design parameters. The uncertainties in the design parameters will decrease when the number of inputs increase, i.e. more information is available. The results of this research may be beneficial to geotechnical reliability-based design.
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