Patterns of Nonlinear Shear Stiffness Degradation of Reconstituted Clay with Different Stress Histories

This paper describes patterns of nonlinear shear stiffness degradation with respect to the stress history of clay. An experimental study using undrained triaxial compression tests was conducted on specimens cut from reconstituted clay samples of kaolinite. The nonlinear pattern of stiffness degradation was analyzed within the frameworks of both the conventional overconsolidation ratio (OCR) and the stress path rotation angle. The experimental data were subsequently interpreted based on the concept of the kinematic sub-yield surface. The pattern of stiffness degradation is more relevant to the rotation angle of the current stress path than the OCR value. The sizes of the sub-yield surfaces are variable. Results show that the kinematic movements of sub-yield surfaces within the overall bounding surface may provide an insufficient tool to fully describe the pattern of stiffness degradation.