Coal

as a typical sedimentary rock

has a naturally anisotropic feature. For simplicity

coal is considered as an isotropic material in the study of coal permeability

and the corresponding isotropic permeability models have been proposed. However

the actual situation of gas-solid coupling in the field and laboratory tests cannot be well reflected by these models. In this paper

coal is treated as transversely isotropic

and an anisotropic permeability model is developed by using different directional modulus reduction ratios as the key parameters. The developed model is further implemented in COMSOL multiphysics software to comprehensively investigate the effect of coal anisotropy on gas diffusion and penetration. Theoretical and numerical results show that different directional modulus reduction ratios ( ) reflect the degree of anisotropy of the coal structure. When is different

the coal permeability is also not the same. Coal permeability is mainly governed by mechanical effects and desorption effects

and meanwhile

these two effects on each direction of the permeability of coal are controlled by boundary conditions. is a reflection of these two effects. Under the uniaxial strain or displacement control boundary condition

the horizontal modulus reduction ratio ( ) has more significant effect on the amount of permeability change in the vertical direction ( ) than on that in the horizontal direction ( ). However

the vertical modulus reduction ratio ( ) has less effect on than on .