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1. Influence of Corrections to Recorded Peak Ground Accelerations due to Liquefaction on Predicted Liquefaction Response During the 2010-2011 Canterbury, New Zealand, Earthquake Sequence

   Upadhyaya, S. (April 2019, Proc. 13th Australia New Zealand Conference on Geomechancs (13ANZCG))

   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. 

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2. Insights into the Liquefaction Hazard in Napier and Hastings Based on the Assessment of Data from the 1931 Hawke’s Bay, New Zealand, Earthquake

   El Kortbawi, M. (April 2019, Proceedings - Australia-New Zealand Conference on Geomechanics)

   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. 

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3. Liquefaction Triggering, Consequences, and Mitigation

   https://doi.org/10.1061/9780784481455.002  

   Green, Russell A.; Maurer, Brett W.; van Ballegooy, Sjoerd (June 2018, Proc. Geotechnical Earthquake Engineering and Soil Dynamics V (GEESD V), Liquefaction Triggering, Consequences, and Mitigation (S.J. Brandenberg and M.T. Manzari, eds.), ASCE Geotechnical Special Publication (GSP) 290)

   The influence of the non-liquefied crust that overlies a liquefied deposit on the severity of surficial liquefaction manifestations has been noted for several decades. In 1985, Ishihara proposed a generalize relationship relating the thicknesses of the non-liquefied crust and of the liquefied stratum to the severity of surficial liquefaction manifestations. Although subsequent studies using data from multiple earthquakes give credence to Ishihara’s relationship, the implementation of the procedure is tenuous for all but the simplest of profiles. In an effort to overcome issues with implementing the Ishihara relationship, new procedures have been proposed for predicting the severity of surficial liquefaction manifestations. The efficacies of two of these procedures are currently being assessed in a study using unique case history data from the 2016, Mw5.7 Valentine’s Day earthquake that impacted Christchurch, New Zealand. Preliminary results from this study show that both procedures yield predictions that are in accord with field observations. However, the final results from the ongoing study are expected to more fully assess the efficacies of these procedures. 

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4. Liquefaction Triggering, Consequences, and Mitigation

   https://doi.org/10.1061/9780784481455.018  

   Upadhyaya, Sneha; Maurer, Brett W.; Green, Russell A.; Rodriguez-Marek, Adrian (June 2018, Proc. Geotechnical Earthquake Engineering and Soil Dynamics V (GEESD V), Liquefaction Triggering, Consequences, and Mitigation (S.J. Brandenberg and M.T. Manzari, eds.), ASCE Geotechnical Special Publication (GSP) 290)

   The liquefaction potential index (LPI) was found to significantly overpredict the severity of observed liquefaction for a large subset of case histories compiled from Canterbury, New Zealand, earthquakes. One potential cause for these overpredictions is the presence of nonliquefiable capping and interbedded strata with high fines-content and/or plasticity that suppress surficial liquefaction manifestations. Herein, receiver-operating-characteristic analyses of compiled Canterbury, New Zealand, liquefaction case histories are used to investigate LPI performance as a function of the soil-behavior-type index averaged over the upper of 20 m (Ic20) of a profile; Ic20 is used to infer the amount of high fines-content, high-plasticity strata in a profile. It is shown that generally: (1) the relationship between computed LPI and the severity of surficial liquefaction manifestations is Ic20-dependent; and (2) the ability of LPI to segregate cases on the basis of observed manifestation severity using LPI decreases with increasing Ic20. In conjunction with previous studies, these findings support the need for an improved index that more adequately accounts for the mechanics of liquefaction triggering and manifestation. 

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5. Surficial liquefaction manifestation severity thresholds for profiles having high fines-content, high-plasticity soils

   https://doi.org/10.1139/cgj-2022-0092  

   Upadhyaya, Sneha; Maurer, Brett W.; Green, Russell A.; Rodriguez-Marek, Adrian; van Ballegooy, Sjoerd (May 2023, Canadian Geotechnical Journal)

   The severity of surficial liquefaction manifestation was significantly over-predicted for a large subset of case histories from relatively recent earthquakes that impacted the Canterbury region of New Zealand. Such over-predicts generally occurred for profiles having predominantly high fines-content (FC), high-plasticity soil strata. Herein, the liquefaction case histories from the Canterbury earthquakes are used to investigate the performances of three different manifestation severity index (MSI) models. The prevalence of high FC, high-plasticity strata in a profile is quantified through the soil behavior type index averaged over the upper 10 m of a profile ( I_c10). It is shown that for each MSI model (1) the threshold MSI value distinguishing cases with and without manifestation increases as I_c10increases and (2) the ability of the MSI to segregate cases with and without manifestation decreases with increasing I_c10. Additionally, probabilistic models are proposed for evaluating the severity of surficial liquefaction manifestation as a function of MSI and I_c10. The approaches presented in this study allow better interpretations of predictions made by existing MSI models, although their efficacy decreases at sites with high I_c10. An improved MSI model is ultimately needed that better accounts for the effects of high-FC, high-plasticity soils more directly. 

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