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.