A state-dependent constitutive model for unsaturated clays is proposed based on the double plastic mechanisms (i.e.

shear sliding and loading collapse mechanisms)

and the coupling between hydraulic hysteresis and stress-strain behavior. In the proposed model

the stress integration at the intersection of two solid phase yield surfaces is addressed using an implicit integration algorithm. The consistent tangent matrix of constitutive model is explicitly derived by considering the relationship between stress and suction. Finally

the numerical simulations of triaxial tests on unsaturated clay are carried out to demonstrate the abilities of the constitutive model. The calculated results of strain-controlled tests on unsaturated soils with different step sizes are compared to demonstrate the convergence and accuracy of the implicit algorithm. The two-dimensional ground consolidation of unsaturated soils is analyzed using the U_DYSAC2 program to demonstrate the validity of the consistent tangent matrix.