Abstract: To investigate the permeability evolution of deep coal under the influence of mining disturbance, two forms of permeability model including the damage and fracture effect were established. These two forms were exponential form and cubic form, respectively. These two permeability models were based on the previous coal permeability model in three-dimensional (3D) stress state. The derivation process included two aspects, i.e., the fracture deformation caused by adsorption and the deterioration of elastic modulus from matrix caused by damage. Meanwhile, the internal swelling ratio and the damage constitutive based on Drucker-Prager failure criterion were introduced into the models. According to permeability tests under conventional triaxial compression, loading-unloading under mining disturbance and changing the gas pressure, the permeability of coal in the tests were analyzed in detail. The results show that these two models can reflect the permeability evolution in the conventional triaxial compression and loading-unloading tests. Moreover, these two models can represent the decrease of coal permeability with the increase of gas pressure under the constant effective confining pressure condition. In the loading-unloading and changing the gas pressure tests, the fitted results in exponential form are slightly better than those in cubic form. This study provides a useful reference for developing the technology of deep coal mining and gas extraction.

Key words: deep coal, permeability, mining disturbance, three-dimensional stress, adsorption and desorption, damage and fracture