A novel permeability model incorporating damage evolution under thermo-hydro-mechanical condition: development and verification

Under the coupling effect of effective stress and temperature, the permeability characteristics of rock under thermo-hydro-mechanical (THM) conditions are complicated. The complexity of permeability under THM conditions is mainly characterized by the non-monotonic variation with effective stress and temperature. The permeability variation under THM condition is mainly controlled by four different mechanisms, including compaction effect of mean effective stress, expansion effect of temperature, damage effect of effective shear stress, and damage effect of temperature. The former two mechanisms cause permeability to decrease, the latter two mechanisms cause permeability to increase. Therefore, based on the cubic model, a novel permeability model considering the four mechanisms described above is proposed in this study. The proposed permeability model is the function of effective stress and temperature. Besides, the permeability impact factor is defined based on the proposed model, which can directly reflect the contribution of effective stress and temperature to permeability. Four sets of permeability data under THM conditions were selected from existing literature to validate the proposed model. The fitted surface accurately describes the variation in the permeability data, which validates the accuracy and applicability of proposed model. Subsequently, the variation of permeability impact factor with effective stress and temperature is discussed.