ROTATION OF PRINCIPAL STRESSES IN GRANULAR MATERIAL DURING SIMPLE SHEAR

Abstract

On the basis of the experimental evidences for the simple shear test of two-dimensional granular model and for the direct shear test of sand, some fundamental problems such as (1) the orientation of the principal stress axes and (2) the relation between the principal axes of stress and those of strain increment are discussed to make the deformation and strength behaviours of granular material clear from a theoretical point of view. The distribution law of contact force, which makes the determination of mean contact force at each contact possible, is successfully applied to calculate the theoretical value with respect to the mobilized stress ratio and the inclination angle of the maximum principal stress axis in the simple shear test. The rotation of the principal stress axes during simple shear occurs in the process of increasing stress ratio, and the principal axes of stress and of strain increment do not generally coincide with each other, at least up to the peak stress ratio. The equations obtained theoretically accord well with the experimental results performed by the present authors and Roscoe, et al. The same principle in regard to the mechanism of strain hardening is also applicable to the direct shear test of sand.