Correcting Liquefaction Resistance of Unsaturated Soil Using Wave Velocity

Explicit empirical relationships for correcting liquefaction resistance of unsaturated soil below the groundwater table using compression wave velocity (V-P) and shear wave velocity (V-S) are derived and evaluated in this paper. The relationships are derived using published laboratory test data for four different sands and one silt material. The laboratory test data based on V-P exhibit less scatter than the test data based on the ratio V-P/V-S. For this reason, the V-P-based relationship is recommended for correcting the liquefaction resistance of unsaturated soil. The influence of loading cycles and relative density on the recommended relationship is investigated. From a review of 40 field case history sites, it is found that in the critical layers at 20% of the sites, average V-P is less than 1,400 m/s, indicating unsaturated conditions. Liquefaction resistances computed for eight field case histories with V-P < 1,200 m/s in the critical layers are corrected and plotted on penetration-and V-S-based liquefaction evaluation charts. The results support the use of the correction for unsaturated conditions below the groundwater table. DOI: 10.1061/(ASCE)GT.1943-5606.0000770. (C) 2013 American Society of Civil Engineers.