Hydraulic-mechanical coupling in claystone is of great importance for repository research, as claystone is considered a possible host rock and hydraulic-mechanical coupled processes can affect the integrity of the barrier. Of particular importance in this context are excavation damage zones and hydraulically-induced microcracks and fractures. In this work, two constitutive equations developed for these hydraulic-mechanical coupled processes are combined in a novel way. The approach exploits the different dominant stress states that prevail in the respective processes. This approach is applied in several numerical simulations for validation and compared with experimental data. The measured data were obtained during gas-injection tests in the scope of the PGZ experiment in the underground laboratory of Bure, France, where the hydraulic-mechanical coupling of the is the Nabla operator claystone was investigated. Five numerical models were calculated, each with a different model configuration, to simulate the excavation damage zone and dilatancy-controlled flow during gas-injection tests. The numerical results show that the developed approach can first satisfactorily predict the extent and behaviour of the excavation damage zone under different stress conditions and the subsequent dilatancy-dependent permeability due to the increased gas pressure.