Quantile value method versus design value method for calibration of reliability-based geotechnical codes

This paper compares two methods for geotechnical reliability code calibration, namely the well known design value method (DVM) based on first-order reliability method and a recently developed method based on quantile, called the quantile value method (QVM). The feasibility of calibrating a single partial factor to cover the wide range of coefficients of variation (COVs) commonly encountered in geotechnical designs is studied. For analytical tractability, a simple design example consisting of one resistance random variable and one load random variable is first examined. A resistance factor is first calibrated using a single calibration case associated with a typical COV. The objective is to evaluate the departure from the target reliability index analytically when this calibrated resistance factor is applied to validation cases associated with a range of COVs. The results show that QVM is more robust than DVM in terms of achieving a more uniform reliability level over a range of COVs. Two realistic geotechnical design examples are studied to demonstrate that the theoretical insights garnered in the simple analytical example are applicable. (C) 2013 Elsevier Ltd. All rights reserved.