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This study outlines a probabilistic cyclic shear strain-based procedure for the determination of the minimum shear strain, γcl, required to initiate liquefaction in gravelly soils. The proposed formulation accounts for the influence of void ratio through the shear wave velocity and the grain size distribution through the coefficient of uniformity, Cu. Separate equations for γcl are derived considering four cyclic resistance models that rely on shear wave velocity as a measure of probabilistic liquefaction resistance. Similarities and differences in the resulting γcl for each of these models are identified. The accuracy and uncertainty of cyclic strain-based models in predicting liquefaction in gravelly soils are demonstrated using existing liquefaction case histories where grain size distributions are available. The excess pore pressure response of gravelly soils subjected to earthquake ground motions is evaluated using a subset of the available liquefaction case histories and the cyclic shear strain and energy-based frameworks and is compared to laboratory test specimens. Although the trends in excess pore pressure generation from critical layers in the case histories are comparable to laboratory-based responses, a greater rate of excess pore pressure generation is calculated for the field cases. The models presented in this study can help identify sites that have a high potential for ground failure when used together with other established models.
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Assessment of an Alternative Implementation of the Dobry et al. Cyclic Strain Procedure for Evaluating Liquefaction Triggering
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.
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- PAR ID:
- 10134688
- Date Published:
- Journal Name:
- Proc. 7th International Conference on Earthquake Geotechnical Engineering (7ICEGE)
- Page Range / eLocation ID:
- 2714-2722
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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