Instrumented 74-mm Dynamic Cone Penetration and Shear Wave Velocity Tests for Assessing Liquefaction in Gravelly Soils Subjected to the 2020 Petrinja, Croatia, Earthquake

The liquefaction of gravelly soils during earthquakes remains a challenging hazard to evaluate because larger soil particles can interfere with traditional in situ tests such as the standard penetration test (SPT) and cone penetration test (CPT). This study investigates six sites affected by the 2020 Mw 6.4 Petrinja, Croatia earthquake, where gravelly liquefaction ejecta was observed. Subsurface investigations included boreholes to define the soil profile, shear wave velocity (Vs) profiling using the multichannel analysis of surface waves (MASW) and horizontal to vertical spectral ratio (HVSR), and large-diameter (74-mm) dynamic cone penetration tests (DPT). At several sites, DPT blow counts increased through silty clay surface layers, whereas CPT tip resistance from companion testing remained constant. The increase in DPT resistance was thus attributed to side friction along the drill rods, and two subsequent DPT soundings were conducted to isolate this effect: (1) a cased DPT (cDPT), where the overlying material was removed and the hole was cased to the target gravelly layer; and (2) an instrumented DPT (iDPT), used to measure the hammer energy transferred to the cone. Corrected DPT blow counts (N120′) and normalized shear wave velocities (Vs1) from critical gravelly layers were evaluated using recent probabilistic DPT- and Vs-based liquefaction triggering models. These methods correctly predicted liquefaction manifestation at each of the sites. Results support the continued development of energy-corrected DPT and Vs-based approaches for liquefaction assessment in gravelly soils and provide valuable case history data to continue refining probabilistic triggering relationships.