Method for developing hardening parameter independent of stress path for geomaterials

Based on the test results of sand, mechanics of internal parameters (plastic volumetric strain and plastic deviator strain) depending on stress path is explained. General equation expressing hardening parameter independent of stress path is proposed. The plastic work and the unified hardening parameters for clay and sand proposed by authors are all special examples as general equation. The combination of the unified hardening parameters and Cam-clay model, and the comparison with the test results, show that this parameter can be used to constitutive model simply and effectively.