True triaxial behavior of sandy soils under both drained and undrained conditions: A discrete element perspective

Abstract

An advanced discrete element servomechanism that can simultaneously and independently control the evolution equations of six stress and strain components without introducing severe stress concentration is implemented. Such a comprehensive series of discrete element method simulations of both drained and undrained behavior of transversely isotropic sandy soils are successfully conducted in the true triaxial setting. During the simulation process, the evolution patterns of the load-bearing structure of the granular specimen are tracked using a contact-normal-based fabric tensor. The simulation results show that sandy soils exhibit more significant non-coaxiality between the loading direction and the major principal direction of the fabric tensor under extension than under compression. Therefore, the fabric of the sandy soils under extension has a stronger tendency to evolve toward the loading direction than that under compression, causing a more significant disturbance to the load-bearing structure. Consequently, compared with the extension loading condition, the transversely isotropic specimen under compression exhibits a higher shear strength and stronger dilatancy under drained conditions and a stronger liquefaction resistance under undrained conditions.

Keywords

granular materials / true triaxial test / discrete element method / fabric evolution

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Funding

The National Natural Science of China(52208366); the Department of Science and Technology of Hubei Province(2023AFB578)