New evaluation formula for sand liquefaction based on survey of Bachu Earthquake in Xinjiang

The in-situ SPT data at 47 sites have been collected in the liquefaction survey of Bachu Ms 6.8 Earthquake, Xinjiang, China. The feasibility of the existing sand liquefaction evaluation methods is analyzed, and a new evaluation formula is proposed. The analysis shows that the current assessment formulae using SPT for sand liquefaction are not applicable in Xinjiang area, which will present obvious risky results. Based on new investigation data, five parameters including seismic intensity, measured SPT values, datum SPT values, water tables and depths of sandy soils are included in the new liquefaction evaluation model. The datum SPT values, the influencing coefficients of water tables and sand depths are gained by a normalized method and by an optimizing method, separately. The characteristic depths of sand are larger than those in the existing Chinese seismic design codes, and the datum SPT values are far larger than those in the code, indicating that the possibility of deep sand liquefaction under low water tables is high in Bachu Earthquake. The successful judging rates by the new formula are 86% and 88% for liquefied sites and for non-liquefied sites, respectively. The proposed new formula can be employed for site liquefaction evaluation and regional code formulation in Xinjiang area.