Updating Uncertainties in Undrained Shear Strengths by Multivariate Correlations

Undrained shear strengths (su) play important roles in geotechnical designs. In the context of geotechnical reliability-based design, reducing uncertainties in su can be an important research topic. There are at least two ways of reducing uncertainties in su: conduct (1) laboratory or (2) in-situ tests to obtain indices or parameters to correlate su indirectly. The way of reducing uncertainties in su can be challenging. The challenge lies in the fact that the so-obtained indices and parameters, e.g. CPT tip resistance, cannot be directly used to estimate su but can estimate su only through correlations. Above all, there is a challenge in combining information: how to reduce uncertainties in su 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. Sets of simplified equations will be obtained through the probabilistic analysis for the purpose of reducing 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 desirable undrained shear strengths. The uncertainties in su 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.