||The development of a coupled elastoplastic damage constitutive model for argillites is presented. Emphasis is put on the description of post-failure and coupled hydromechanical behavior of argillites during the desaturation/resaturation processes. A short summary of experimental investigations is given in the first part, which shows an important plastic deformation coupled with damage and a significant influence of water content on the mechanical behavior of argillites. Based on the framework of poroplasticity and continuum damage mechanics, a general constitutive model is proposed for the poromechanical behavior of argillites in both saturated and unsaturated conditions. Main features observed in experiments are taken into account, in particular the elastic degradation due to microcracks, residual strength, coupling between plastic deformation and induced damage, influence of water content on plastic flow, variation of permeability induced by microcracks as well as the deformation generated in the desaturation/resaturation processes. The performance of the model is examined by comparing numerical simulations with test data in representative load paths. Finally, the model is applied to hydromechanical coupling study of four time-dependent tests subjected to a step change in relative humidity.