A New $V_s$-Based Liquefaction-Triggering Procedure for Gravelly Soils

Liquefaction assessment has primarily been performed using in situ penetration testing, but this practice has become problematic for gravelly soils. For example, standard penetration test (SPT)- or cone penetration test (CPT)-based correlations can become unreliable owing to interference with large gravel particles, while the Becker Penetration Test, commonly used for gravelly soil, can be relatively expensive and requires conversion to an equivalent sand blow count. As an alternative, probabilistic liquefaction-triggering curves have been developed based on shear-wave velocity ($V_s$) using gravel sites in the $M_{w}7.9$ Wenchuan earthquake. These curves have significant uncertainty because of the small data set. In this study, new probabilistic triggering curves for gravel liquefaction have been developed based on a $V_s$ data set. The data set consists of 174 data points (96 liquefaction and 78 no liquefaction) obtained from 17 earthquakes in seven countries within different geological environments. The larger data set better constrained the curves and reduced the range between the 15% and 85% probability of liquefaction curves, indicating less uncertainty. These triggering curves for gravel are shifted to the right relative to comparable curves for sand, indicating that higher $V_s$ values are necessary to preclude liquefaction. To account for the influence of the different earthquake magnitudes on liquefaction, a magnitude scaling factor (MSF) was developed specifically for gravel. This curve falls within the range of other MSF curves for sands based on $V_s$.