INVESTIGATING CYCLIC BEHAVIOR OF FINE-GRAINED SOILS USING DIRECT SIMPLE SHEAR TESTS: INFLUENCE OF PLASTICITY AND LOADING CONDITIONS

Date

2026-6-25

Author

ZARZOUR, MOUTASEM

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This research presents a performance-based evaluation of the monotonic and cyclic response of fine-grained soils, quantifying the coupled effects of density, plasticity, stress history, confinement, and initial static shear stress. Utilizing a constant volume, cyclic direct simple shear (CV-CDSS) testing program on reconstituted Adapazarı silt and silt-bentonite mixtures, the experimental matrix investigates the combined influences of plasticity index, overconsolidation ratio, vertical effective consolidation stress, post-consolidation void ratio, liquidity index, and initial static shear stress ratio. The results demonstrate that the cyclic softening of fine-grained soils spans a continuum from effective-stress-driven cyclic liquefaction in non-plastic silts to strain-driven cyclic mobility in plastic mixtures. These responses are evaluated probabilistically within a maximum likelihood framework (MLE). A sequence of non-parametric correlation analysis, collinearity diagnostics via variance inflation factor (VIF), and penalized model selection yields statistically robust multivariate models for monotonic undrained shear strength and cyclic shear stress. They systematically decouple overlapping physical influences, quantifying the applicability of and sensitivity to normalization of cyclic demand with initial vertical effective stress or monotonic undrained shear strength. Moreover, semi-empirical adjustment factors are proposed to evaluate normalized cyclic strength when initial confining stress, overconsolidation ratio, plasticity Index and initial monotonic shear stress states deviate from the reference ones. The proposed predictive models enable incorporating different sources of uncertainties in the evaluation of cyclic softening response of fine-grained soils.

Subject Keywords

Transitional Fine-Grained Soils, Cyclic Softening, Constant Volume Direct Simple Shear, Probabilistic Multivariate Regression

URI

https://hdl.handle.net/11511/119773

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Graduate School of Natural and Applied Sciences, Thesis