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.