Anisotropic Permeability of Coal Subjected to Cyclic Loading and Unloading

An experimental investigation on the anisotropic permeability of coal under cyclic loading and unloading conditions is presented in this article. The results show that coal permeability decreases with increasing hydrostatic stress. The relationship between coal permeability and applied stress was quantified using an improved power model. The cyclic loading and unloading were found to induce an irreversible permeability reduction, which tended to be diminished with increasing loading/unloading cycles. The anisotropic permeability of the studied coal is notable, and it was found to nonlinearly decrease with an increase of the angle between the direction of flow and the direction of bedding planes (θ). The relationship between permeability and θ can be quantified using an exponential model with an anisotropic parameter (λ). Several factors (e.g., loading cycles, stress) influencing the anisotropic permeability are discussed in this article.