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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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Selecting Factor of Safety against Liquefaction for Design Based on Cost Considerations
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.
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- PAR ID:
- 10134690
- Date Published:
- Journal Name:
- Proc. 7th International Conference on Earthquake Geotechnical Engineering (7ICEGE)
- Page Range / eLocation ID:
- 5419-5426
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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