A unified elasto-plastic constitutive model for sandy and clayey soils accounting for at-rest condition

Taking advantages of some existing two-surface soil constitutive models in a critical state framework, a unified two-surface constitutive model was developed for rigorous simulation of elasto-plastic deformation of different soils such as loose and dense sands, normally and over-consolidated clayey soils subjected to any type of monotonic loadings. Employing the dilatancy parameter, the strain-softening and stress-dilatancy were described using non-associated flow rule to generalise the application of the model to different soils under various stress states. The applicability of the proposed model was validated comparing the numerical simulations with the existing experimental data for variety of soils subjected to different phases of monotonic loadings. The model was found to be capable of simulating drained and undrained behaviour of clayey and sandy soils under triaxial stress conditions as accurate as the constant stress-ratio loading state. The results also demonstrated the ability of the model to determine the at-rest earth pressure coefficient (K-0) for variety of soilssuitable to be applied to the geotechnical problems affected by this parameter such as piles groups and retaining earth structures. While the formulation of hardening parameter in the integration scheme is based on volumetric and deviatoric plastic strains, the simulation of dilatancy response especially in dense sands showed an excellent agreement with the experimental data.