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Undrained or constant volume direct simple shear (CDSS) tests are commonly used to evaluate the liquefaction triggering characteristics of cohesionless soils. However, while the American Society for Testing of Materials (ASTM) has developed standards for monotonic direct simple shear testing, they have not developed a standard for CDSS. As a result, herein the authors review their test database and assign “grades” A-D to different aspects of the tests, e.g.: accumulated shear strain and imposed shear stress on the specimen during the consoli-dation phase, and maximum axial strain that occurs during the cyclic phase of constant volume CDSS testing. Additional grades are also assigned to the tests based on unusual behaviors in the stress paths. Acceptance criteria based on the cumulative test scores are then proposed for “high” quality tests. The slope of the relationship between cyclic stress ratio (CSR) and number of cycles to liquefaction (NL) is influenced by the exclusion of tests using the acceptance criteria, even though the excluded tests were of sufficient quality to have been included in most published studies. 

Probabilistic assessments of the potential impact of earthquakes on infrastructure entails the consideration of smaller magnitude events than those generally considered in deterministic hazard and risk assessments. In this context, it is useful to establish if there is a magnitude threshold below which the possibility of triggering liquefaction can be discounted because such a lower bound is required for probabilistic liquefaction hazard analyses. Based on field observations and a simple parametric study, we conclude that earthquakes as small as moment magnitude 4.5 can trigger liquefaction in extremely susceptible soil deposits. However, for soil profiles that are suitable for building structures, the minimum earthquake magnitude for the triggering of liquefaction is about 5. We therefore propose that in liquefaction hazard assessments of building sites, magnitude 5.0 be adopted as the minimum earthquake size considered, while magnitudes as low as 4.5 may be appropriate for some other types of infrastructure. 

Paleoliquefaction studies provide valuable information for seismic hazard analyses in areas where the return period of moderate to large events is longer than the duration of the historical earthquake catalog (e.g., Central-Eastern and Pacific Northwest United States). Toward this end, paleoliquefaction studies require accurate and detailed assessments of individual features and of the extent of the paleoliquefaction field for the event, with the difficulty of accurately interpreting field observations increasing in areas where recurrent liquefaction was triggered by spatiotemporally clustered paleo events. Accordingly, undisturbed features formed by recurrent liquefaction during the 2010–2011 Canterbury, New Zealand, earthquake sequence were studied to facilitate interpretation of paleoliquefaction analogs. Silt drapes demarcated multiple episodes of liquefaction in the sand blows, with the thickness of the silt drapes correlating to the fines content of the liquefied source stratum. However, no ubiquitous trends in the spatial sorting of grain sizes in the coarser fraction of the ejecta underlying silt drapes were observed. This study provides a modern analog to recurrent paleoliquefaction evidence and has important implications for interpretation of seismic hazards. 

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. 

The stress-based simplified procedure is the most widely used approach for evaluating liquefaction triggering-potential of sandy soils. In deterministic liquefaction evaluations, “rules of thumb” are typically used to select the minimum acceptable factor of safety (FS) against liquefaction triggering, sometimes guided by the strain potential of the soil once liquefied. This approach does not fully consider the value of the infrastructure that will potentially be impacted by the liquefaction response of the soil. Accordingly, in lieu of selecting FS based solely on precedent, Receiver Operator Characteristic (ROC) analyses are used herein to analyze the Standard Penetration Test (SPT) liquefaction case-history database of Boulanger & Idriss (2014) to relate FS to the relative consequences of misprediction. These consequences can be expressed as a ratio of the cost of a false-positive prediction to the cost of a false-negative prediction, such that decreasing cost-ratios indicate greater consequences of liquefaction, all else being equal. It is shown that FS = 1 determined using the Boulanger & Idriss (2014) procedure inherently corresponds to a cost ratio of ~0.1 for loose soils and ~0.7 for denser soils. Moreover, the relationship between FS and cost ratio provides a simple and rational approach by which the project-specific consequences of misprediction can be used to select an appropriate FS for decision making. 

Evaluations of Liquefaction Potential Index (LPI) in the 2010-2011 Canterbury earthquake sequence (CES) in New Zealand have shown that the severity of surficial liquefaction manifestations is significantly over-predicted for a large subset of sites. While the potential cause for such over-predictions has been generally identified as the presence of thick, non-liquefiable crusts and/or interbedded non-liquefiable layers in a soil profile, the severity of surficial liquefaction manifestations at sites that do not have such characteristics are also often significantly over-predicted, particularly for the Mw 6.2, February 2011 Christchurch earthquake. The over-predictions at this latter group of sites may be related to the peak ground accelerations (PGAs) used in the liquefaction triggering evaluations. In past studies, the PGAs at the case history sites were estimated using a procedure that is conditioned on the recorded PGAs at nearby strong motion stations (SMSs). Some of the soil profiles on which these SMSs were installed experienced severe liquefaction, often with an absence of surface manifestation, and the recorded PGAs are inferred to be associated with high-frequency dilation spikes after liquefaction was triggered. Herein the influence of using revised PGAs at these SMSs that are in accord with pre-liquefaction motions on the predicted severity of surficial liquefaction at nearby sites is investigated. It is shown that revising the PGAs improved these predictions, particularly at case history sites where the severity of the surface manifestations was previously over-predicted and could not be explained by other mechanisms. 

Evaluations of Liquefaction Potential Index (LPI) in the 2010-2011 Canterbury earthquake sequence (CES) in New Zealand have shown that the severity of surficial liquefaction manifestations is significantly over-predicted for a large subset of sites. While the potential cause for such over-predictions has been generally identified as the presence of thick, non-liquefiable crusts and/or interbedded non-liquefiable layers in a soil profile, the severity of surficial liquefaction manifestations at sites that do not have such characteristics are also often significantly over-predicted, particularly for the Mw 6.2, February 2011 Christchurch earthquake. The over-predictions at this latter group of sites may be related to the peak ground accelerations (PGAs) used in the liquefaction triggering evaluations. In past studies, the PGAs at the case history sites were estimated using a procedure that is conditioned on the recorded PGAs at nearby strong motion stations (SMSs). Some of the soil profiles on which these SMSs were installed experienced severe liquefaction, often with an absence of surface manifestation, and the recorded PGAs are inferred to be associated with high-frequency dilation spikes after liquefaction was triggered. Herein the influence of using revised PGAs at these SMSs that are in accord with pre-liquefaction motions on the predicted severity of surficial liquefaction at nearby sites is investigated. It is shown that revising the PGAs improved these predictions, particularly at case history sites where the severity of the surface manifestations was previously over-predicted and could not be explained by other mechanisms. 

Hawke’s Bay is situated on the east coast of the North Island of New Zealand and has experienced several earthquakes in the past during which triggered liquefaction. The 1931 Hawke’s Bay earthquake is particularly interesting because it was one of the most damaging earthquakes and the deadliest earthquake in New Zealand’s history. This study provides insights into the actual versus predicted liquefaction hazard in Napier and Hastings. Towards this end, the simplified Cone Penetration Test (CPT)-based liquefaction triggering evaluation procedure proposed by Boulanger & Idriss (2014) (BI14) is used in conjunction with Liquefaction Severity Number (LSN) framework to predict severity of surficial liquefaction manifestations across the region for the 1931 MS7.8 Hawke’s Bay event. A comparison of the results with post-event observations suggests that the liquefaction hazard is being over-predicted. One possible cause for this over-prediction includes the shortcomings liquefaction damage potential frameworks to predict the severity of surficial liquefaction manifestations in silty soil deposits. This study demonstrates how historical earthquake accounts in a region can be used to assess the risk of the region from future earthquakes.