Microstructure consideration with plastic spin and multiple back-stresses for large strain problems in soils

The effect of sub-structure changes in geo-materials is investigated here by incorporating the plastic spin in the anisotropic modified Cam Clay Model. The plastic spin is formulated as a function of internal variables in the constitutive equation. Dual back-stresses are incorporated as internal variables. The short range back-stress is used for the intragrain back-stress while the long range back-stress is used for the inter-grain back-stress. A linear evolution equation is used for the short range back-stress, and a non linear evolution equation is used for the long range back-stress. Individual evolution equations are used for the plastic spins for the short range back-stresses and for the long range back-stresses, respectively. To simulate the behavior of saturated soils at large strains, the coupled theory of mixtures with elasto-plasticity in an updated Lagrangian reference frame is adopted. The results showed that the effects of the long range back-stress are more significant for the large strain region while that of short range back-stress are more affective for the small strain region.