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The stress-based simplified liquefaction triggering procedure is the most widely used approach to assess liquefaction potential worldwide. However, empirical aspects of the procedure were primarily developed for tectonic earthquakes in active shallow-crustal tectonic regimes. Accordingly, the suitability of the simplified procedure for evaluating liquefaction triggering in other tectonic regimes and for induced earthquakes is questionable. Specifically, the suitability of the depth-stress reduction factor (rd) and magnitude scaling factor (MSF) relationships inherent to existing simplified models is uncertain for use in evaluating liquefaction triggering in stable continental regimes, subduction zone regimes, or for liquefaction triggering due to induced seismicity. This is because both rd,which accounts for the non-rigid soil profile response, andMSF,which accounts for shaking duration, are affected by the characteristics of the ground motions, which can differ among tectonic regimes, and soil profiles, which can vary regionally. Presented in this paper is a summary of ongoing efforts to regionalize liquefaction triggering models for evaluating liquefaction hazard. Central to this regionalization is the consistent development of tectonic-regime-specific rd and MSF relationships. The consistency in the approaches used to develop these relationships allows them to be interchanged within the same overall liquefaction triggering evaluation framework. 

The severity of surface manifestation of liquefaction is commonly used as a proxy for liquefaction damage potential. As a result, manifestation severity index (MSI) models are more commonly being used in conjunction with simplified stress-based triggering models to predict liquefaction damage potential. This paper assesses the limitations of four MSI models. The different models have differing attributes that account for factors influencing the severity of surficial liquefactionmanifestations, with the newest of the proposed models accounting more factors than the others. The efficacies of these MSI models are evaluated using well-documented liquefaction case histories from Canterbury, New Zealand, with the deposits primarily comprising clean to non-plastic silty sands. It is found that the MSI models that explicitly account for the contractive/dilative tendencies of soil did not perform as well as the models that do not account for this tendency, opposite of what would be expected based on the mechanics of liquefaction manifestation. The likely reason for this is the double-counting of the dilative tendencies ofmedium-dense to dense soils by theseMSI models, since the liquefaction triggering model, to some extent, inherently accounts for such effects. This implies that development of mechanistically more rigorous MSI models that are used in conjunction with simplified triggering models will not necessarily result in improved liquefaction damage potential predictions and may result in less accurate predictions. 

The operator of the Groningen gas field is leading an effort to quantify the seismic hazard and risk of the region due to induced earthquakes, including overseeing one of the most comprehensive liquefaction hazard studies performed globally to date. Due to the unique characteristics of the seismic hazard and the geologic deposits in Groningen, efforts first focused on developing relationships for a Groningen-specific liquefaction triggering model. The liquefaction hazard was then assessed using a Monte Carlo method, wherein a range of credible event scenarios were considered in computing liquefaction damage-potential hazard curves. This effort entailed the use of a regional stochastic seismic source model, ground motion prediction equation, site response model, and geologic model that were developed as part of the broader regional seismic hazard assessment. No to minor surficial liquefaction manifestations are predicted for most sites across the study area for a 2475-year return period. The only sites where moderate surficial liquefaction manifestations are predicted are in the town of Zandeweer, with only some of the sites in the town being predicted to experience this severity of liquefaction for this return period. 

Seismic compression is the accrual of contractive volumetric strain in unsaturated or partially saturated sandy soils during earthquake shaking and has caused significant distress to overlying and nearby structures, to include the 2007, Mw6.6 Niigata-ken Chuetsu-oki, Japan earthquake. Of specific interest to this study is the seismic compression that occurred during this event at the Kashiwazaki-Kariwa Nuclear Power Plant (KKNPP) site. What makes this case history of particular value is that the motions at the site were recorded by a free-field downhole array (Service Hall Array, SHA) and the magnitude of the seismic compression was accurately determined from the settlement of soil around a vertical pipe housing one of the array seismographs. The seismic compression at the site was ~10-20 cm. The profile at the site was well characterized by in-situ tests and laboratory tests performed on samples from the site, which allows seismic compression models to be calibrated. The study presented herein compares the predictions of the simplified and non-simplified forms of the expanded Byrne model. The predictions are in good accord with field observations, but the slight under-prediction by the non-simplified model may relate to estimated soil properties, assumed orientation of the ground motions and accounting for multidirectional shaking, and/or the numerical site response analyses used to compute the variation of the shear strains during shaking at depth in the soil profile. 

Seismic compression is the accrual of contractive volumetric strain in unsaturated or partially saturated sandy soils during earthquake shaking and has caused significant distress to overlying and nearby structures. The phenomenon can be well-characterized by load-dependent, interaction macro-level fatigue theories, which means that the nature of the accumulation of volumetric strain is a function of the absolute amplitude and sequencing of pulses in the loading function. One model that captures this behavior and that can be used to predict seismic compression is the expanded Byrne cyclic shear-volumetric strain coupling model. However, one potential implication of the load-dependent, interaction macro-level fatigue behaviour is that ground motion orientation will influence predicted settlements. To examine the significance of this, the seismic compression that occurred at the Kashiwazaki-Kariwa Nuclear Power Plant (KKNPP) site during the 2007, Mw6.6 Niigata-ken Chuetsu-oki, Japan, earthquake is analyzed using the expanded Byrne model. The horizontal motions recorded at the site by a down-hole array during this event are rotated in 5° increments and the predicted settlements due to seismic compression are computed. The predicted settlements range from 12.3 to 16.1 cm, with a geometric mean of the values for various orientations being 13.8 cm. These results are in general accord with the post-earthquake field observations and highlight the sensitivity of predicted magnitude of the seismic compression to ground motion orientation. 

ASCE 7-16 details how the peak ground acceleration (PGA) should be determined for evaluating liquefaction triggering, with this PGA reflecting the influence of a range of earthquake magnitudes on a site’s seismic hazard. Similarly, the Finn and Wightman magnitude-weighting scheme can be used to account for the full range of magnitudes influencing the seismic hazard at a site, where the weights are derived from a site’s seismic hazard deaggregation data. However, the deaggregation data for the seismic hazard maps for the Central/Eastern U.S. are only available for rock motions and not motions at the surface of the soil profile. The authors explore this issue by comparing the weighted average magnitude scaling factors (MSF) and depth-stress weighting factor (rd) values for multiple sites in the Western U.S. developed using deaggregation data for rock motions and for motions at the surface of the soil profiles. Based on these comparisons, the authors found that using the PGA deaggregation data for rock conditions yield similar weighted averages for MSF and rd as those computed using deaggregation data for the PGA at the surface of the soil profile. 

Despite its fundamental basis and many positive attributes, the cyclic strain approach has not been embraced by practice for evaluating liquefaction triggering. One reason for this may be the need to perform cyclic laboratory tests to develop a relationship among excess pore water pressure, cyclic strain amplitude, and number of applied strain cycles. Herein an alternative implementation of the strain-based procedure is proposed that circumvents this requirement. To assess the efficacy of this alternative implementation, Standard Penetration Test field liquefaction case histories are evaluated. The results are compared with both field observations and with predictions from a stress-based procedure. It was found that the strain-based approach yields overly conservative predictions. Also, a potentially fatal limitation of the strain-based procedure is that it ignores the decrease in soil stiffness due to excess pore pressure when representing the earthquake loading in terms of shear strain amplitude and number of equivalent cycles.