Study On The Fracture Evolution Of Coal-Rock Mass Of Coalfield Fire With Thermo-mechanical Coupling Effects

Coal and rock fracture is the main oxygen supply channel to support the coal fire area` s continuous development. The fracture change of coal fire area overburden rock involves thermal coupling problem, it is closely related to the state of the fire area. so studying the change rule of rock fracture and permeability with thermal coupling effect is conducive to understand the development of underground coal fire under the condition of anaerobic process and predict the development trend of coal fire and provide theoretical support to make specific fire control measures. This paper take a coal fire area in Xinjiang as a prototype, introduced the discrete element theory, studied the change rule of rock fracture and permeability with thermal coupling effect by using the PFC2 D particles flow code. The main research contents and results are as follows:Based on the sandstone mechanical parameters tests and mesoscopic parameters calibration standard, numbers of numerical simulation of calibration process were carried out by using PFC2 D program, and the mesoscopic parameters which reflect the fire area rock`s actual mechanics characteristics were obtained. Take these mesoscopic parameters into the PFC model of fire area, and obtained the Coal bed mining strata caused by the crack distribution, and its regional permeability of initial value before the fire.By using the SDT-Q600 synchronous thermal analyzer, the pyrolysis process of coal sample from fire area under the condition of pure nitrogen atmosphere were tested.Based on the mining model obtained, different temperature field were put into the burning layer, and analyszed fracture and permeability change of each region in the overburden rock in different conditions. The laws are as follows: Under the action of temperature, Fire area of overburden rock fracture and permeability decreases as temperature increases the change trend of rising; But the decrease in the strength of strata caused by the temperature changes in the main; Regardless of the traces of burning layer coal burning, burning area overall permeability change is relatively small; In the process of temperature changes in the fire area, the common role of the burning of coal and the temperature will result in great changes of overburden rock fracture and permeability, under the influence of temperature and burning of coal seam, master in the coal and rock fracture trend is obvious.In the heritage of coal burning and under the joint action of temperature, Strata fracture number began to accelerate in 380 ℃, after 500 ℃the rising trend began to slow. In addition to the permeability of mined-out area is basically remain unchanged, other areas of overburden rock permeability with the increase of the fracture number and larger.