DEM Analysis of Mechanical Behavior of Unsaturated Silt under Strain-Controlled Constant Stress Ratio Compression Tests
Publication: International Journal of Geomechanics
Volume 21, Issue 10
Abstract
The three-dimensional discrete element method (DEM) is employed to investigate the macro- and microscopic mechanical behaviors of unsaturated silt subjected to one-dimensional (K0) and constant stress ratio loadings. A DEM sample was prepared by installing a contact model considering rolling and twisting resistances and the van der Waals force. Capillary forces were installed at contacts to represent the unfilled water effect. Strain-controlled one-dimensional and constant stress ratio compression tests were then simulated on the specimens with different constant matric suctions and stress ratios (η = q/p). The discrete element simulation results reproduce the primary macroscopic mechanical behavior observed in laboratory tests. Shear failure occurs in specimens compressed under stress ratios exceeding the strength slope M, while volumetric yielding occurs in specimens compressed under very small stress ratios η ≪ M. The compression test under a constant stress ratio larger than M reaches the critical state characterized by not only a constant stress state and void ratio, but also a constant effective particle number, (mechanical) an average coordination number, and fabric anisotropies of contact normals and contact forces. The contribution of normal contact forces to the deviator stress predominates over tangential contact forces throughout the simulation. The capillary stress (capillary force-induced stress tensor) anisotropy decreases under isotropic compression but increases under anisotropic compression (η = 1.25). The mechanical average coordination number versus mean stress is independent of the stress ratio and the matric suction. Fabric evolutions indicate that the rearrangement of contact forces is much quicker than that of contact normals at the beginning of compression.
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Acknowledgments
The authors gratefully acknowledge financial support from the China National Natural Science Foundation (Grant Nos. 51809193 and 51890911) and the China Postdoctoral Science Foundation (Grant No. 2018M631741). The authors express great thanks to the anonymous reviewers for their careful work and thoughtful suggestions that have helped improve this paper substantially.
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Published In
International Journal of Geomechanics
Volume 21 • Issue 10 • October 2021
Copyright
© 2021 American Society of Civil Engineers.
History
Received: Aug 13, 2020
Accepted: Jun 25, 2021
Published online: Aug 9, 2021
Published in print: Oct 1, 2021
Discussion open until: Jan 9, 2022
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