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1. 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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2. 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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3. 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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4. Assessing the Limitations of Liquefaction Manifestation Severity Index Prediction Models

   Green, R.A. (July 2022, Proc. 4th Intern. Conf. Performance-based Design in Earthquake Geotechnical Engineering (PBD-IV 2022))

   L. Wang, J.-M. Zhang (Ed.)

   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. 

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5. CPT-based liquefaction case histories compiled from three earthquakes in Canterbury, New Zealand

   https://doi.org/10.1177/8755293021996367  

   Geyin, Mertcan; Maurer, Brett W; Bradley, Brendon A; Green, Russell A; van Ballegooy, Sjoerd (January 2021, Earthquake Spectra)

   null (Ed.)

   Earthquakes occurring over the past decade in the Canterbury region of New Zealand have resulted in liquefaction case-history data of unprecedented quantity. This provides the profession with a unique opportunity to advance the prediction of liquefaction occurrence and consequences. Toward that end, this article presents a curated dataset containing ∼15,000 cone-penetration-test-based liquefaction case histories compiled from three earthquakes in Canterbury. The compiled, post-processed data are presented in a dense array structure, allowing researchers to easily access and analyze a wealth of information pertinent to free-field liquefaction response (i.e. triggering and surface manifestation). Research opportunities using these data include, but are not limited to, the training or testing of new and existing liquefaction-prediction models. The many methods used to obtain and process the case-history data are detailed herein, as is the structure of the compiled digital file. Finally, recommendations for analyzing the data are outlined, including nuances and limitations that users should carefully consider. 

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