THE INITIAL STRESS LINE AND MODIFIED MOHR-COULOMB CRITERIONS FOR UNDISTURBED SOIL

The particular structure, which was constructed by the initial stress in consolidation, is the key role to answer the remarkably mechanical difference between remolded soil and undisturbed soil. The yield surface for remolded soil in a three principle stress space, always takes the isoclinic line as its axis due to isotropy. It is rational that the initial stress line, but not the isoclinic line, should be set as the axis of the yield surface for undisturbed soil because the stress state in original position is not spherical. As a foreword, the generalized yield shear stresses which had been achieved from some true triaxial tests at constant p, were analyzed with respect to a loading angle. Subsequently, the concept of an initial stress line was put forward owing to the initial stress state of undisturbed soil. And the relationship between an isoclinic line and an initial stress line was discussed. Together with the generalized plasticity mechanics, three modified Mohr-Coulomb yield criteria, namely translation model, translation model, and revolution model, were built to simulate the shear yield of undisturbed soil. The yield traces of the first two modified criteria are all located on a traditional π plane. While the yield trace of the revolution model is located on a χ plane, which is vertical to the initial stress line. Therefore, the first two models can be utilized to simulate true triaxial tests at constant p. And the last one can be employed to simulate true triaxial tests at σ₁+K₀σ₂+K₀σ₃=c or data transformed from a π plane to a χ plane. Reference verification has illustrated that the revolution model derivated from Mohr-Coulomb yield criterion could reflect the structure and anisotropy of undisturbed soil in mechanics. Furthermore, every variable parameter in the third model has an explicit physical meaning.