Study On Theory And Application Of High Gassy Seam Rockburst

There is some basic knowledge to the mechanism of common rockburst, the conventional method and technique of rockburst forecast and prevention formed already, however, the special exposition is few about the mechanism, forecast and prevention of rockburst occurring in high gassy seam so far. Wulong and some other coal mines in Fuxin Coal Area were selected as experiment mine in this paper. The mechanism, forecast and prevention technique of the rockburst occurring in high gassy seam were studied with the method combining theoretical analysis with spot practice and test in laboratory. The main contents are as follows.1. Spot investigation and test in laboratory.Some specific data of test mines were collected and analyzed through spot investigation, such as geological structure, rockburst, inherent gas and its pumping.The physical and mechanical properties of coal sample were determined through tests in laboratory. Their properties are apparent density, compression strength, elastic modulus, gas permeability, water permeability, contact angle, relation of compression strength and gas content, relation of elastic modulus and gas content, variation of mechanical properties with water ratio in the different soaking water time and so on.2. Theoretical research of rockburst occurring in high gassy coal seam.The mechanism of rockburst occurring in high gassy coal seam and gas gushing after rockburst were revealed. The distinction and connection were discovered between rockburst occurring in gassy seam and burst of coal and gas. The theory and its mathematical model of rockburst occurring in high gassy seam were established. This theory was applied to analyze the rockburst of tunnel and coal face.There is a critical value of gas pressure. When gas pressure is greater than this critical value, the Klinbenberg effect disappears, the gas adsorbing quantity reaches saturation, the effective stress coefficient decreases and the permeability increases if gas pressure increases. This is the behavior of high gassy seam.The action of gas to coal mass is called porous pressure, and the coal mass undertake effective stress. The process of its deformation and rapture is controlled by the effective stress. In this process the cracks appear and expend. When effective stress is greater than compression strength in some areas the coal mass become to strain softening media that is instable. Total system consists with instable media in some areas and stable media in outer areas. In process of the excavation this system understands the coupling action of gas adsorption, desorption, transfusion and coal deformation, its balance state is instable. In situation of external disturbance its balance will be lose and rockburst will occur.When the rockburst occurs a band is formed around the rockburst point. The pressure and density of gas decrease in this band. The gas desorption, diffusion and transfusion happened at the same time, a great quantity of gas will pour out and continue after rockburst.By comparative analysis between rockburst occurring in gassy seam and burst of coal and gas it show that the breeding process is similar completely but occurring process and source of energy is different. When the coal seam deformation system undertake compression stress and lose stability the rockburst will occur. When tensile effective stress is greater than tensile strength of coal the system appear tensile instability and the burst of coal and gas will occur.The occurring conditions relate to gas pressure and mechanical properties of coal. The critical load of tunnel rockburst increases if gas pressure increases. The critical load of coal face increases if gas pressure and effective stress coefficient increase.3. Research of forecast technique of rockburst occurring in high gassy seam.Drilling bits index of gas seam was determined and the inference law of someparameters were discussed. Comparative analysis was made to no gas situation. Some technological parameters of drilling bits method were determined. The correctness and feasibility were verified through actual operation. Drilling bits index of gassy seam is lower, it decreases if gas pressure and effective stress coefficient increase.4. Research of prevention technique of rockburst occurring in high gassy seam.Theories of driving and replacement of water and gas were established throughporous medium model and double-porous medium model respectively. The expression of water injection time was obtained by solving fundamental equation of plane radical flow. The feasibility of water injection into coal seam to prevent rockburst in Fuxin Mining Area was analyzed. The technological parameters and process were improved. It was verified through actual operation. The prevention scheme of rockburst occurring in high gassy seam, dispelling rockburst danger measure and gas gushing prevention method were put forward.The physical and mechanical properties of coal will be transformed after soaking water. The face of full water injection the frequency and intensity of rockburst will decrease greatly. The water injection into coal seam is a process of driving and replacement of water and gas among coal seam. The water injection time increases if porous ratio, gas pressure and water injection radius increase, the time decreases if permeability and water injection pressure increase. The technological parameters consist of radius, quantity, time and pressure of water injection, closing length and so on.