In this research, the thermomechanical formulation proposed by Ziegler and formalized by Houslby and Puzrin to build up hyperplastic constitutive models is applied to the case of unsaturated materials. The mechanical model is based on two main equations: the free energy and the dissipation functions. The former represents the elastic behavior while the latter accounts for the plastic behavior of the material. The dissipation function can be split into two parts: one represents the flow rule and the other the yield surface. The shape of the yield surface can be modified by a single parameter while the plastic flow is of the non-associated type and can also be modified with a single parameter. The yield surface rotates at the origin depending on the anisotropy of the material. The volumetric behavior of the soil is related to the distance between its current state and the normally consolidated, the critical state, and the unloading-reloading lines. The model considers the phenomenon of suction hardening and employs Bishops equation to determine the effective stress on unsaturated materials. The mechanical model is coupled to a porous-solid model that can simulate the soil-water retention curves during wetting-drying cycles and accounts for the hydro-mechanical coupling phenomenon. In that sense, this procedure does not require pre-establishing the shape of the yield surface or the flow rule. The resulting model is a three-dimensional hyperplastic coupled model that requires few parameters. Comparisons between experimental and numerical results show that the proposed model can simulate the behavior of soils with fair precision.