An anisotropic coal permeability model that considers mining-induced stress evolution, microfracture propagation and gas sorption-desorption effects

Anisotropic coal permeability plays an important role in the simultaneous extraction of coal and gas from deep underground. In this study, first, the representative elementary volume of a coal mass is determined based on the natural microfracture distribution in coal. Then, an anisotropic coal permeability model that considers the complex stress evolution process, microfracture propagation and gas sorption-desorption effects was established to comprehensively study the coupled process of the actual mining-induced anisotropic mechanical behaviors and the gas seepage phenomena in the coal. The main characteristic of this model is coupled the stress-fracture-seepage analyses on the mechanical behavior of coal in terms of complex stress evolution. The presented model is verified using two different experimental observations, and a precise mathematical expression of the stress evolution processes induced by different mining layouts is presented to perform the coupled analyses using the presented model. The simulation results exhibit good agreement with the experimental data and reflect the overall trends of the test results fairly well, and the simulation results can appropriately represent the actual mining-influenced coal mechanical behavior. Thus, the model is highly adaptable for simulating various stress boundary conditions and engineering disturbance processes and is applicable for conducting numerical studies on coal fracture propagation, gas sorption-desorption effects and complex mining-induced mechanical behavior. Therefore, this model provides a theoretical basis for further analyses.