GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 3.2 ___ GNGTS 2023 Fig. 1 – a) Gradation curves of liquefied gravelly soils (dashed yellow lines) in comparison with the grain size ranges proposed by Tsuchida & Hayashi (1971) and b) Chart of magnitude vs. epicentral distance to gravel liquefaction sites and available reference correlations (Salvatore et al., 2022). Furthermore, Salvatore et al. (2022) compared the liquefaction susceptibility of sands and gravels in terms of magnitude vs. epicentral distance (Fig. 1b), using the gravel liquefaction case histories (black dots in Fig. 1b) and liquefaction curves available for sands (Ambraseys, 1988; Galli, 2000; Castilla & Audemard, 2007; Maurer et al., 2015). As shown in Fig. 1b, the triggering boundary for the gravel liquefaction can be assumed similar to the boundary curves already available for sands, highlighting that gravel liquefaction is not only associated with strong seismic events. Methods The liquefaction assessment of gravelly soils through the geotechnical laboratory characterization has always been a challenge because of the difficulties in taking undisturbed or partly disturbed samples and the high costs. Consequently, classical in situ tests such as Standard Penetration Test (SPT), developed for clean sandy soils, were adapted to gravelly soils. Although the use of the SPT-based approach correctly estimates the liquefaction potential in loose gravel with low penetration resistance, after the application of a correction factor (e.g., Kokusho & Yoshida, 1997), the results may be inaccurate when the penetration resistance increases, therefore new penetration tests with larger diameter tips have been developed to overcome these problems. In particular, the dynamic cone penetration test (DPT), that consists of a 74 mm cone driven continuously by a 120 kg hammer dropped from one meter, using a drilling rig or a simple SPT tripod system (Chinese Design Code, 2001), has been introduced and used firstly by Cao et al. (2013) and later by Rollins et al. (2022) to develop a procedure for the liquefaction assessment in gravelly soils. Furthermore, Cao et al. (2011) also developed a liquefaction triggering curve VS-based for gravelly deposits, using the MW 7.9 Wenchuan dataset, and similarly to the DPT chart, Rollins et al. (2022) realized probabilistic liquefaction triggering curves based on VS data from a worldwide