Calculation procedure for three dimensional state of stress and strain in axial-torsional testing for constitutive behavior of geo-materials

Laboratory experiments on long and thin hollow cylinder soil specimens subjected to a combination of normal and shear stresses under confined conditions is valuable for evaluating their three dimensional constitutive behavior The present paper discusses a new approach for interpreting the complete state of stress and strain during isotropic consolidation and subsequent phase of applying shear stress. A clear rationale for assumptions involved in updating the specimen geometry, correcting for latex membrane effects while undergoing axial and/or torsional deformations, appropriate expressions for evaluating the current state of stress and strain are presented. The approach presented for the interpretation of measured data (initial specimen geometry, axial load, axial deformation, torque, rotation, pore pressure, volume change, and cell pressure) is based on minimum number of assumptions, and are justified by the theory of elasticity. The new formulation and where appropriate, comparisons with those used by previous researchers are presented in this paper The proposed method was applied to interpret the results of a combined axial-torsional test data on Kaolin clay performed at a constant inclination of major principal stress of 60 degrees with the axis of rotational symmetry.