Coal permeability model and evolution law considering water influence

Coal is usually in a state of coexistence of gas and water during the changing process of the mining environ- ment. In order to explore the reaction mechanism between water and coal permeability,the coal containing gas heat-flu- id-solid coupling device of three axis servo seepage and isothermal adsorption device was used to carry out the experi- mental studies on the permeability of the coal when the increased pore pressure are under different water contents. Based on the interaction between water film and pore surface,and the effect of disjoining pressure between water films, considering the contribution rate of compression deformation and slippage effect to coal seepage,a permeability model that considers the effects of moisture was constructed. Furthermore,the variation of coal adsorption and seepage under different water conditions is analyzed. The results show that ① under different water-bearing conditions,the adsorption amount of coal increases with the increase of pore pressure. With the increase of water content,the adsorption amount decreases gradually,and the sorption-induced deformation also has the same trend. At the same time,the adsorption deformation changes with the adsorption of coal. ② The water in the coal rock is easy to form an adsorption water film on the surface of the pore crack to occupy the channel of gas seepage. And gaseous and liquid water molecules can re- strict gas flow. Therefore,gas flow decreases as the water content increases. Under the condition of constant water con- tent,the permeability of coal decreases first and then decreases with the increase of pore pressure. Under constant pore pressure,the permeability decreases significantly with the increase of water content. ③ Considering the effects of com- pression deformation,sorption-induced deformation,water content and water film thickness on the fracture width,a per- meability model under gas-water environment was constructed. The permeability value of coal is in good agreement with the measured data,which can better characterize the water-bearing law of coal permeability. Meanwhile,relevant re- search results also provide a theoretical guidance for the management of coal mine gas disasters.