| The paper conducted in-depth research on gas pressure field characteristics and implication in deep coal seam mining systematically by using combining research methods of theoretical analysis, numerical simulation, field test. Research on correlation of gas pressure and flow characteristics with stress under different stress states was carried out. Large-scale computational model which can be reflected the deposit characteristics of gas pressure was established based on the occurrence of coal seam gas and the mining sequence of each working face, and the distribution of gas pressure in coal seam and the macro evolution of gas pressure field was be reappeared in the mining process of each working face through the numerical simulation. The binary high-order polynomial inversion mathematical model of gas pressure field was set up based on the measured data of gas pressure and geophysical inversion theory, and the inversion study on gas pressure field was done, and the three dimensional distribution characteristics of gas pressure field and its control equation were obtained. The risk and the type of dynamic disasters were analyzed based on the main influence factors such as stress state of coal and rock, gas pressure and physical and mechanical properties, etc. For the problem that rock cross-cut coal uncovering was easy to induce dynamic disasters, the dynamic disasters prevention and control technique of hydraulic punching stress-relief was put forward under the background of the lower yard in track uphill and the field test was conducted, and an apparent effect of outburst elimination was obtained. The main contents and conclusions are as follows:1. Study on stress correlation of gas pressure and flow characteristics in coal seamDirectional permeability calculation model is set up based on the principle of equivalent displacement; Flow characteristics under different stress state and stress correlation of gas pressure distribution are analyzed through theoretical analysis and numerical simulation. The main conclusions are as follows:(1) Flow abilities of porous medium in different directions are quite different. The flow of porous medium has obvious direction, by the limited of directional permeability flow-direction is the direction of big permeability under the action of stress and pore pressure gradient in priority. Quantitative calculation model of directional permeability is established based on the principle of equivalent displacement. The model can reflect permeability vector of the space in any directions.(2) There is an advantage flow effects in coal seam. Gas flows first along the strike direction of crack; the advantage flow effect gradually strengthens when the fracture stress changes in a direction advantageous to crack open. The influence of stress to fissure flow and gas pressure distributions is greater than the influence of pore. Stress controls flow field of the coal seam and population distribution pattern of gas pressure.(3) The gas pressure in coal seam follows the order at the same time under same stress state: the gas pressure in penetrated fracture was bigger than that of part penetrated fracture, the gas pressure in porous media was the least; Flow field and gas pressure distribution of penetrated fracture is most affected by stress. Second is the part penetrated fracture. Minimum is pore medium.(4) Seepage flow velocity in the fissure is bigger than that of part penetrated fracture and pore under the same stress state. There is a velocity advantage effect. Stress controls seepage velocity field distributions characteristics of coal seam.2. The mathematical model of gas pressure field inversion is established based on the geophysical inversion theory. Control equation and spatial distribution pattern of coal seam gas pressure curved surface are obtained.Based on the measured data of gas pressure and geophysical inversion principle, the invert and predicted research on the coal seam gas pressure field are carried out by using damping least-square method. According to the result of the in-situ stress measurement, the simulation study on the regularities of distribution of the initial ground stress field in mine is conducted by using multiple linear regression method. On the basis of simulation results of the coal seam gas pressure field and ground stress field, the influence law of ground stress field to the gas pressure field distribution characteristics is analyzed. The main conclusions are as follows:(1) The dual higher order polynomial inversion mathematical model of coal seam gas pressure field is established based on the geophysical inversion theory for the discomfort of coal seam gas pressure field inversion problems. A kind of dual higher order polynomial gas pressure field inversion method based on the damping least square method is formed.(2) Dual higher order polynomial gas pressure field inversion method is applied to the inversion research of coal seam static gas pressure field law according to gas pressure measured data. The overall distribution characteristics of gas pressure field are obtained. Control equation of the three-dimensional distribution of coal seam gas pressure field is got. Coal seam gas pressure of other sites in plate areas can be effectively predicted.(3) The stress state of coal seam has obvious effects on the gas pressure gradient. Gas pressure gradient of a certain direction is formed. The rule of approximate vertical between the largest coal seam gas pressure gradient and maximum horizontal principal stress is revealed.3. Regularity of mining stress response of coal seam gas pressure is revealed.Taking the technical conditions of coal mining and the gas storing condition as the background, the distributing feature and evolutionary regularity of the mining pressure field, the response characteristics of gas pressure are researched by the method of numerical simulation; based on some main influence factors such as stress status of coal and rock mass, gas pressure, physical and mechanical properties of coal and etc, the degree of contribution of each factor and its relevant types of dynamic disaster which are likely to cause are analyzed. The main conclusions are as follows:(1) In the process of mining, stress and gas pressure appeared local increase and decrease, and experienced the dynamic evolution process that increased first and then decreased and moving forward regularly along with the coal mining. In the process of stress state evolution, gas pressure changes with the evolution of stress state, the evolution of gas pressure is controlled by the change of stress state, and the gas pressure is controlled by the evolution of stress.(2) Under the influence of mining disturbance, in the coal and rock body there are reciprocal cross fracture network, gas flow in the fracture network obeys the advance flow route principle of minimum flow resistance and maximum gas pressure gradient, and it flows toward the direction of minimum flow resistance and maximum gas pressure gradient. Gas pressure and flowing gas fields evolved dynamicly along with the change of the stress state of the coal and rock body, the evolution of gas pressure and the flowing gas fields are controlled by the change of stress state, the gas pressure and the flowing gas fields are controlled by the evolution of stress. Regularity of mining stress response of coal seam gas pressure is revealed.(3) Coal and gas outburst is influenced by many factors, based on the stress state of the coal and rock mass, the gas pressure, the physical and mechanical properties of coal, geological structure and other major effect, the dynamic disasters of coal and gas outburst hazard is analyzed. According to the magnitude of the effect of each factor, it can be divided into the dynamic disasters oriented by stress and dynamic disaster oriented by stress and gas.4. The macro evolution regularity of coal seam gas pressure field is revealed.With the background of mining conditions and gas pressure occurrence characteristics in different working faces of the 11-2 coal seam, overall distribution characteristics of gas pressure in coal seam and the evolution of gas pressure field in the ordinal mining process of working faces were researched through the method of numerical simulation. The main conclusions are as follows:(1) In the process of mining, the equilibrium state of the gas occurrence that is close to the working face goaf is broken. Gas continuously flows to the mining space through the fracture network channel that formed by excavation disturbance, the macro direction flow that centered on the goaf is generated, and then the remit that centered on the goaf is formed. Near the working face mining, the coal seam gas that is close to working face received multiple releases, the gas pressure has experienced decreased in multiple different degrees. Gas pressure presented three-dimensional distribution pattern of valley shape.(2) After coal seam mining, coal seam gas pressure that is close to the goaf decreased obviously, gas pressure unloading zone with different unloading width is formed by taking the goaf as the center. With the extension of time, the scope of the gas pressure unloading zone expanding gradually and finally tends to be stable., the gas pressure unloading zones are formed connected and overlapping when the adjacent working face are mined, and the phenomenon increases the range of the gas pressure unloading zone and forms a wide range low gas pressure area, to a certain extent, the effect of gas pressure unloading is enhanced.5. The dynamic disasters prevention and control technique of hydraulic punching stress-relief in rock cross-cut coal uncovering is put forward. The industrial test was implied. An apparent effect of outburst elimination is obtained.For the problem that rock cross-cut coal uncovering is easy to induce dynamic disasters, taking the cross-cut coal uncovering in track up hill lower yard for research object, the dynamic disasters prevention and control technique of hydraulic punching stress-relief in rock cross-cut coal uncovering is put forward and the field test is conducted, and an apparent effect of outburst elimination is obtained. The main conclusions are as follows:(1) The advantage of gas flow and dynamic disaster risk matrix is built. The advantages of the gas flow and risk of dynamic disaster is analyzed comprehensively.(2) Coal has gone through a process of multiple fracturing – crushing – extruding in the hydraulic punching stress-relief test. The integrity of coal body was undermined. The overall mechanical properties of coal and rock mass were weakened, the original stress was reduced and the stress state of coal and rock was improved. The stress field of coal seam has experienced several evolutions, and finally it was in the stable state of low stress.(3) The dynamic disasters prevention and control technique of hydraulic punching stress-relief reduced the gas pressure and gas content of the coal seam, and improved the occurrence state of gas and the distribution of the gas pressure field. The gas pressure field of coal seam has experienced several evolutions, and finally it was in the stable state of low gas content and low gas pressure, the obvious outburst elimination was achieved.(4) Transform from extracting gas for reducing the gas pressure to hydraulic punching stress-relief test for reducing the gas pressure is realized. Time and cost for extracting gas in rock cross-cut coal uncovering process are saved and the efficiency of rock cross-cut coal uncovering is improved. |
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