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This study outlines a probabilistic cyclic shear strain-based procedure for the determination of the minimum shear strain, γcl, required to initiate liquefaction in gravelly soils. The proposed formulation accounts for the influence of void ratio through the shear wave velocity and the grain size distribution through the coefficient of uniformity, Cu. Separate equations for γcl are derived considering four cyclic resistance models that rely on shear wave velocity as a measure of probabilistic liquefaction resistance. Similarities and differences in the resulting γcl for each of these models are identified. The accuracy and uncertainty of cyclic strain-based models in predicting liquefaction in gravelly soils are demonstrated using existing liquefaction case histories where grain size distributions are available. The excess pore pressure response of gravelly soils subjected to earthquake ground motions is evaluated using a subset of the available liquefaction case histories and the cyclic shear strain and energy-based frameworks and is compared to laboratory test specimens. Although the trends in excess pore pressure generation from critical layers in the case histories are comparable to laboratory-based responses, a greater rate of excess pore pressure generation is calculated for the field cases. The models presented in this study can help identify sites that have a high potential for ground failure when used together with other established models. 

Abstract: On April 3, 2024, a magnitude 7.4 earthquake, known as the 2024 Hualien Earthquake, struck offshore Hualien, Taiwan, at a depth of 15.5 km. Overall, the negative societal impacts were limited, despite varying levels of impact to the infrastructure, including power outages affecting over 308,000 households, landslides obstructing roads, bridge collapses, and railway deformations. Taiwan’s fast recovery is credited to its robust earthquake preparedness and disaster mitigation strategies. Given this event’s strong potential to generate new knowledge, StEER considered activating its standard Level 1 response. However, upon consulting with colleagues in the National Center for Research on Earthquake Engineering (NCREE), StEER opted to instead play a supporting role to NCREE efforts already locally documenting the event, and an official response page was instituted at the StEER website to house any products generated by this collaboration. NCREE’s rapid access to the affected area enabled a unique form of Preliminary Virtual Reconnaissance Report (PVRR) that included both data from third-party sources and from the NCREE-field-collected data. 

This study presents the use of controlled blasting as a source of seismic energy to obtain the coupled, dynamic, linear-elastic to nonlinear-inelastic response of a plastic silt deposit. Characterization of blast-induced ground motions indicate that the shear strain and corresponding residual excess pore pressures (EPPs) are associated with low frequency near- and far-field shear waves that are within the range of earthquake frequencies, whereas the effect of high frequency P-waves are negligible. Three blasting programs were used to develop the initial and pre-strained relationships between shear strain, EPP, and nonlinear shear modulus degradation. The initial threshold shear strain to initiate soil nonlinearity and to trigger generation of residual EPP ranging from 0.002 to 0.003% and 0.008 to 0.012%, respectively, where the latter corresponded to ~30% of Gmax. Following pre-straining and dissipation of EPPs within the silt deposit, the shear strain necessary to trigger residual excess pore pressure increased two-fold. Greater excess pore pressures were observed in-situ compared to that of intact direct simple shear (DSS) test specimens at a given shear strain amplitude. The reduction of in-situ undrained shear strength within the blast-induced EPP field measured using vane shear tests compared favorably with that of DSS test specimens.