The stress-strain behavior of Ottawa F65 sand is investigated through an extensive series of constant volume stress-controlled cyclic direct simple shear (CDSS) tests performed at different densities, overburden pressures, and static shear stresses prior to cyclic shearing to quantify their effects on the cyclic strength of Ottawa F65 sand. Results of the CDSS tests are used in the constitutive model calibration exercise for the Liquefaction Experiments and Analysis Project (LEAP-2022). The collected database of CDSS tests is used to develop an Artificial Neural Network (ANN) model capable of predicting Ottawa F65 liquefaction strength for a specified set of relative density, overburden pressure, static shear stress ratio, and cyclic shear stress ratio. After training, validation and testing, the ANN model is further assessed using blind prediction of the liquefaction strength in new CDSS tests for a relative density and overburden stress that are not available in the training dataset. CDSS tests under similar conditions were then carried out in the laboratory for validation of the ANN model. The comparisons of the predictions with the experimental results have demonstrated the ANN model predictive capability for liquefaction strength and its sensitivity to changes in relative density, overburden stress and cyclic stress ratio.
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Quality Assurance Criteria for Cyclic Direct Simple Shear Tests for Evaluating Liquefaction Triggering Characteristics of Cohesionless Soils
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.
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- NSF-PAR ID:
- 10134681
- Date Published:
- Journal Name:
- Proceedings of the XVII ECSMGE-2019
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Conference Paper:
- https://doi.org/10.32075/17ECSMGE-2019-0470
