Reducing the Transformation Uncertainty for the Mobilized Undrained Shear Strength of Clays

Practical undrained shear strength s(u) test results, such as the su values from field vane (FV) and unconfined compression (UC) tests, cannot be used directly as design values. However, they are correlated with the design value of s(u), referred to as the mobilized undrained shear strength s(u)(mob). This study derives the transformation equations that convert practical s(u) results (e. g., FV and UC test results) into the mean value and the coefficient of variation (COV) of s(u)(mob). The derivations are based on the multivariate probability distribution previously constructed by the authors that models the correlations among s(u) values from various s(u) test modes. An important feature of the transformation equations is that they accept multiple practical s(u) test results, so the transformation uncertainty of s(u)(mob) can be reduced further by incorporating more practical tests. This reduction of transformation uncertainty can be exploited to economize design in a reliability-based design framework. The effectiveness of the resulting transformation equations is demonstrated and verified using real case histories. (C) 2014 American Society of Civil Engineers.