Calibrating design factors to assess liquefaction triggering potential for Canadian sites

Abstract

The cyclic resistance ratio and cyclic stress ratio (CSR) are used as the basis for liquefaction triggering potential assessment in design codes and standards. The National Building Code of Canada (NBCC) adopts the 2475-year return period of the annual maximum peak ground acceleration, a2475, reported by the 6th generation of the Canadian seismic hazard map, to evaluate CSR and assess liquefaction triggering potential. However, the results of probabilistic liquefaction hazard analysis (PLHA) indicate that the annual probability of liquefaction triggering potential for assessed sites by using the code approach is, in general, not equal to 1/2475. To overcome the reliability inconsistency, in this study, the reliability-based calibration of the design factor to be used to scale a2475 is carried out based on PLHA. The empirical relations for design factor as functions of depth of the soil layer with different time-averaged shear wave velocity in the upper 30 meters of the soil profile (VS30) and depth of the groundwater table for sites are developed based on the calibration results. The considered VS30 values correspond to the site Class C, D and E stipulated in NBCC. It is shown that the use of the calibrated site-dependent design factor can lead to the assessed site having a consistent annual probability of liquefaction triggering potential near 1/2475.