Applicability of soil-type index for shear wave velocity-based liquefaction assessment

The current simplified liquefaction assessment method based on the shear-wave velocity, V_s has uncertainties about how the fine contents change the V_s-based liquefaction resistance. According to the simplified method, for a given V_s, the cyclic resistance ratio (CRR) increases with an increase in fine contents. However, field investigations recently revealed that for various silty sands, the correlation between CRR and V_s is soil-type index dependent and not specific for all sand-silt mixtures with the same fine contents. Therefore, a detailed experimental research program is performed in this study to clarify the effect of the soil-type index on the shear wave velocity and CRR correlation. In the first part of the present study, the cyclic resistance of sand mixed with non-plastic (NP) fines (dry weight of 0%, 5%, 15%, and 35%) was investigated using cyclic direct simple shear (CDSS) tests. Seismic cone penetration (SCPT) tests were performed inside the large-scale box to facilitate normalized cone penetration resistance (q_c1N) and shear wave velocity measurements on the soils used in the CDSS tests. A new correlation was proposed between the q_c1N and normalized shear wave velocity (V_s1) using the soil-type index I_c representing the behavior of soil. Then, CRR-V_s1 correlation was obtained experimentally for four distinct ranges of soil-type index. Finally, the results of this study and the proposed CRR-V_s1 trends in other investigations were used to discuss the soil-type dependent V_s-based liquefaction susceptibility zones.