Experimental investigation of the effects of density and soil fabric to SPT and Vs measurements in sandy soils for liquefaction assessment

This is the authors' abstract. We don't add key points for this paper.

Experimental studies on Standard Penetration Test (SPT) and shear wave velocity V s measurements were performed using a pressurized calibration chamber. The present study investigated the effects of soil fabric, which have been identified as the primary factor determining soil liquefaction resistance under comparable stress states and yet difficult to be assessed by conventional simplified methods, along with the effect of density. Silica sand model grounds were prepared at loose and dense conditions (relative density D r about 40 % and 80 %) with adjustment in the pluviation process to induce differences in the soil fabric, then consolidated to a mean effective stress of approximately 30 kPa at the middle of chamber specimen. Based on the V s values measured, the difference in the small-strain stiffness G 0 for a given D r was about 18 % to 22 %. Under constant stress conditions, almost equal blow counts N SPT were recorded in two specimens of similar D r regardless of the difference in V s . The findings indicated that N SPT was incapable of reflecting the discrepancy in soil fabric, as evidenced by the varying V s ( G 0 ) values at a given relative density. Further laboratory results from cyclic undrained triaxial tests on loose sand samples prepared under equivalent conditions to those of the chamber specimens revealed notable discrepancies in liquefaction resistance. Samples of higher V s , stronger fabric were more resistant to cyclic undrained loading; and this is in agreement with previous research. Comparisons were also made in estimating cyclic resistance ratio CRR by several SPT and V s based simplified methods, as well as a recently developed empirical relationship of V s - CRR in which the relative density were normalized. The different roles of N SPT and V s should be judged correctly in order to carry out more accurate assessment of liquefaction resistance. New approaches that could collectively evaluate relative density and soil fabric effects, for instances from N SPT and V s , are thought to be beneficial in liquefaction risk assessment.