Macro-micromechanical approaches for non-coaxiality of coarse grained soils

Abstract

For coarse grained soils, their principal stress directions may change when the water level of embankment dam varies instantaneously. In this loading case, the principal directions of stress and strain rate will become non-coaxial. In an effort to model non-coaxial behavior, a modified three-dimensional non-coaxial model is developed in the context of vertex yield (tangent plasticity) theory. Discrete Element Method (PFC) incorporating user-defined interparticle contact models is also employed to gain an insight into microscopic mechanism of non-coaxiality. The analysis focuses on non-coaxial behaviors under simple shear condition. It has been shown that the proposed non-coaxial model gives good predictions for non-coaxiality with reference to microscopic observations while the classical coaxial model fails to simulate the non-coaxial behaviors. In general, non-coaxiality as a result of the rotation of principal stress, is large at a small shear strain, and inclined to become negligible with increasing shear strain. For coarse grained soils, their non-coaxiality tends to largely depend on the initial normal pressure, where a larger degree of non-coaxiality can be observed at a higher pressure. coarse grained soils, non-coaxiality, particle flow code, simple shear Citation:Qian J G, Huang M S, Sun H Z. Macro-micromechanical approaches for non-coaxiality of coarse grained soils.

Improved Boundary Conditions for a 3D DEM Simple Shear Model

“…In previous DEM studies, the agreement of experimental results and simulated result is widely used to validate DEM models [3][4][5]. Asadzadeh and Soroush [6] studied the shear behavior of glass bead with drained simple shear test.…”

“…During shear, the two walls rotate at a constant angular velocity. Qian et al [4] used left and right walls to model the rings in a 2D model, and the walls rotate during shear. Asadzadeh and Soroush [6] modelled the rings as small rigid walls in a 3D model, and the walls have linearly varied rate of shearing during shear in which the top ring has a zero velocity and the bottom ring has a velocity of 0.1 mm/s.…”

Numerical evaluation of three non‐coaxial kinematic models using the distinct element method for elliptical granular materials

“…It has been demonstrated [1][2][3][4][5][6][7][8][9][10][11][12][13] that non-coaxiality plays a key role in the fundamental mechanical behavior of geo-materials and in many geotechnical engineering problems that involve the rotation of the principal stresses. Hence, non-coaxiality should be considered when developing plasticity models for granular material [14][15][16]. Starting from the kinematic theory, various plasticity models have been proposed to describe 'fully developed' planar plastic flow of granular material.…”