Development of design factors for seismic liquefaction hazard-consistent design and evaluation

Seismic-induced liquefaction can cause damage to structures and infrastructure systems. The design checking equation for assessing the liquefaction potential is based on the results from the cone penetration test or the standard penetration test (SPT). Chinese design codes for assessing the liquefaction potential are based on SPT results, and the critical SPT blow count is evaluated based on the specified return period value of the peak ground acceleration (PGA), a_T. However, using a_T alone to assess the liquefaction potential may not achieve a consistent annual probability of liquefaction triggering, P_AL, because seismic events with different combinations of PGA and earthquake magnitude contribute to P_AL. To overcome this drawback, the present study conducted probabilistic liquefaction hazard analysis (PLHA) to calibrate the adjustment or design factors for designing or checking the liquefaction potential. The calibration considered the tolerable annual failure probabilities and detailed seismicity information applicable to the Chinese mainland. It focused on 31 major Chinese cities and different combinations of the groundwater depth, saturated sandy/silty layer embedment depth, and soil properties. Using the calibrated design factors for the considered combinations, empirical equations for evaluating the design factors were developed for practical use. It was shown that without considering such calibrated design factors in evaluating liquefaction potential, the P_AL obtained can vary substantially, and the use of the calibrated design factors reduces such variability. The effects of using the safety factor for designing or checking the liquefaction potential on the implied P_AL were also evaluated and presented.