Coal Structure System And Law Of Gas Seepage During Adjacent Coal Seam Mining

It will result in a series of chain reactions, such as the depressurization of thesurrounding rock, the redistribution of the stress, the partition of the stress formed in therock when the adjacent coal seam is mining. Then the rock is damaged, fractured furtherand broken at last. The permeability of the rock also increases, then the methane desorbs,diffuses, seeps, etc. Because of the gas outburst is a disaster in the coal mining, theclarification of the gas migration characteristics will be a prerequisite to guarantee safety inproduction of the coal seam contained gas. In light of this, this paper take the adjacentlayers of coal seam mining as the subject, comprehensive use of the theory such asstructural mechanics, rock mechanics, fluid mechanics, mining engineering, and numericalcalculation to propose the simplified structure model of the adjacent coal and surroundingrock, and give the internal forces analytical solution of the structure system. In this paper,the movement, deformation and stress evolution of the surrounding rock during theadjacent seam mining is studied, and the leaky gas controlling fluid-solid couplingequations of the adjacent seam are also established. To validate the problem, the numericalmethod is applied to analysis the migration law of the gas in the nearby coal seam. Theresearch provides theoretical basis for the gas outburst prevention, and also providestheoretical guidance for the reasonable arrangement bore when the gas is draining. Themain contents about this paper are as follows:(1) The fracture damage mechanism of the coal and rock mass structure is described,and the stress state in different parts of the rock is analyzed. Then the structure simplifiedmodel of the adjacent coal and surrounding rock is proposed. The loads distribution and theinternal force expressions are also given.(2) A numerical analysis method, FLAC3Dis applied to simulating the law of stressevolution in the surrounding rock. According to the stress and the volumetric strain, theforces and the fracture development in different regions are analyzed. The results show thatthe coal-rock-arch structure is reasonable.(3) With the deformation constitutive equation of the rock, the continuity equation ofthe gas, the dynamic evolution equation of the porosity and permeability coefficient, thegas fluid-solid coupling equations in a single seam and surrounding rock are built, and theleaky gas controlling fluid-solid coupled equations of the adjacent seam are also set up.(4) Using solid mechanics module, hydrodynamic module and PDE mode of the finiteelement software which called COMSOL Muliphisics, the leaky gas controlling fluid-solidcoupling equations of the adjacent seam are calculated. The law of gas pressure, porosityand permeability coefficient in the coal-rock at different moments are analyzed. The influence on the porosity and permeability coefficient with the mined length and depth isalso analyzed. At last the gas velocity field is analyzed.