Cyclic behavior of sand under non-uniform shear stress waves. Issue 143 (April 2021)

• Record Type: Journal Article
• Authors: ElGhoraiby, Mohamed A.; Manzari, Majid T.
• Is Part Of: Soil dynamics and earthquake engineering. Issue 143(2021)
• Publication Date: 2021-04
• Subjects: Liquefaction -- Lateral spreading -- Cyclic direct simple shear tests (CDSS) -- Ottawa F65 sand; Soil dynamics -- Periodicals; Earthquake engineering -- Periodicals; Sols -- Dynamique -- Périodiques; Génie parasismique -- Périodiques; 624.176205
• DOI: 10.1016/j.soildyn.2021.106590
• Languages: English
• ISSNs: 0267-7261

Abstract

Abstract: During an earthquake, soil deposits are often subjected to complex stress/strain time histories that are quite different from the simplified ones used in laboratory tests for evaluation of the stress-strain-strength of these soils. To mimic the stress/strain time histories experienced at different depths of a mildly sloping soil deposit, a series of direct simple shear tests were conducted on Ottawa F65 sand specimens. The trends observed in these experiments were then used to estimate the lateral spreading of mildly sloping saturated deposits of the same sand subjected to various base motion time histories measured in the centrifuge tests conducted as part of an international research project (Liquefaction Experiment and Analysis Project, LEAP-2015 and LEAP-2017). In each CDSS test, after imposing the initial stress state, the specimen was subjected to non-uniform stress waves that resembled the shear stress time histories likely to develop in the LEAP-2015 and LEAP-2017 centrifuge specimens. A total of 17 CDSS tests were performed on specimens with relative densities of approximately 66%. Initial vertical and shear stresses were imposed on each soil specimen to correspond to the state of stress in a mildly sloping soil layer at two depths of about 4 m and 3 m. A ramped sinusoidal shear stress wave similar to the ramped sinusoidal base motion used in the LEAP centrifuge experiments was employed. The test results displayed a consistent trend between the peak cyclic stress ratio and the permanent shear strain that developed in the soil. The effects of overburden stress on the magnitude of permanent deformations were observed. Smaller initial vertical stress resulted in a more dilative response and smaller permanent shear strain. The observed permanent shear strain vs. peak cyclic stress ratio curves were then used to predict the lateral spreading of mildly sloping deposits tested in the LEAP-2015 and LEAP-2017 centrifuge experiments. Reasonably close correlation between the predicted and measured displacements were obtained. The developed dataset, made publicly available on DesignSafe-CI, can be used for calibration, evaluation, and further development of constitutive models for liquefiable soils. Highlights: An experimental study was presented on liquefaction-induced permanent strain on sloping grounds. 17 CDSS tests were conducted to model the stress-strain response of liquefiable sloping ground soil at different depths. Non-uniform cyclic shear stress was subject to the soil to mimic the stresses induced by an earthquake. A close agreement was observed between the results and previously conducted centrifuge experiments. The results obtained from the element tests were used to predict the lateral spreading observed by LEAP centrifuge tests.