Liquefaction Assessment at Gravel Sites in Croatia Based on Vs and DPT Blow count
Please login to view abstract download link
Liquefaction of loose saturated soil results in significant damage to civil infrastructure in nearly every major earthquake event. The loss of shear strength from liquefaction can lead to bearing capacity failure and settlement of buildings as well as lateral spreading on relatively flat slopes. Although liquefaction is most common in loose saturated sands, a significant number of liquefaction case histories have been reported in gravelly soil profiles. Assessing liquefaction resistance in gravelly soils is challenging because the large particle size can interfere with the relatively small diameter of the standard penetration test (SPT) and the cone penetration test (CPT) to artificially increase resistance. To deal with this problem, liquefaction triggering curves have recently been developed based on a large diameter (74 mm) dynamic cone penetrometer (DPT) blow count and on normalized shear wave velocity, Vs1, which are less affected by gravel size particles. While these triggering curves are based on field case histories, the curves are poorly constrained in some areas. Therefore, additional field case histories continue to be highly desirable. This paper describes an investigation of six gravel sites in Croatia that liquefied in the 2020 Mw6.4, Petrinja, Croatia earthquake. At each site, a borehole was completed to define the soil profile and material properties. In addition, a DPT sounding was performed along with shear wave velocity profiling using the Multi-channel Analysis of Surface Waves (MASW) approach with an active source, or array technique based on ambient vibration measurements using seismic nodes deployed in a 2D configuration. At some sites, the DPT blow count increased as the penetrometer passed 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 and provided appropriate blow counts. The measured blow count and shear wave velocities in the criti at these sites correctly predicted liquefaction using recent probabilistic DPT- and Vs1-based triggering curves.