Liquefaction Assessment at Gravel Sites in Croatia Based on Vs and DPT Blow count

Abstract

Liquefaction of loose saturated soil poses a significant threat to civil infrastructure during major earthquake events. Although liquefaction is most common in loose saturated sands, numerous liquefaction events in gravelly soil profiles have been reported. Assessing liquefaction resistance in gravelly soils is challenging because large particle sizes can interfere with the standard penetration test (SPT) and the cone penetration test (CPT). To address this challenge, recent efforts have focused on developing liquefaction triggering curves based on a large diameter (74 mm) dynamic cone penetrometer (DPT) blow count and normalized shear wave velocity, Vs1, which are less affected by gravel-sized particles. While based on field case histories, the curves are poorly constrained in some areas; additional case histories continue to be highly desirable. This paper describes an investigation of six gravel sites that liquefied in the 2020 Mw6.4, Petrinja, Croatia earthquake. At each site, boreholes were completed to define the soil profile, accompanied by DPT soundings and shear wave velocity profiling using the Multi-channel Analysis of Surface Waves (MASW) approach. At some sites, the DPT blow count increased through a silty clay surface layer even though the CPT cone resistance remained constant in this layer. This increase was thus attributed to side friction on the drill rods during penetration. Subsequent DPT tests performed after casing through the silty clay eliminated the rod friction. The measured blow count and shear wave velocities in the critical layers at these sites correctly predicted liquefaction using recent probabilistic DPT- and Vs1-based triggering curves

Full Paper