Research On Strata Movement And Pressure-relief Gas Drainage Of Short-distance And Under-protective Steep Seam Mining

Due to the particularity of the steep seam occurrence, coal is crushed failure seriously. Most steep seam is high gas or outburst seam. Many research findings revealed that protective seam mining binding pressure-relief gas drainage are the safest and most effective local prevention of coal and gas outburst. Based on protective seam mining in Li Gou mine of Yi ma mining group as engineering background, utilizing theoretical analysis, laboratory experiments, numerical analysis and spot experiments;the paper analyses mining strata movement and fracture dynamic evolution, the dynamic variation of stress about the short-distance and under-protective steep seam mining; established pressure-relief gas migration with coal and rock deformation air-solid coupling model adapting to protective seam mining. The paper utilizes COMSOL Multi-physics to carry out numerical simulation of the short-distance and under-protective steep seam mining binding pressure-relief gas drainage, which is applied in the field of engineering. The main research results and conclusions are:With protective seam working face advancing, fractures gradually developed, from bottom to top, from the generation, development to the closure, which was a dynamic process. Bedding fracture development is the major, small scale crossing fracture development is the local. Bedding fractures and crossing fractures go through protective seam and protected seam. The roof does not appear large range collapse,mainly the slowly sinking. Mining influencing range spreads to protected seam, but protective seam mining conditions are not destroyed. Effected by digging gangue filling,maximum deflection of roof is less than that of the first caving period in the normal exploitation stage. Fracture development and strata movement provide effective channel for pressure-relief gas delivery and gas drainage. Stress pressure-relief maximum position and rock movement maximum position basically coincided. With the influence of mining, it presents variation of original stress, stress concentration, stress drop, stress recovery, the inclined upper relief-degree is higher than that of the lower.Evolution models of the porosity and permeability are obtained, according to the effective stress principle of the coal containing gas, matrix adsorption swelling /desorption shrinkage deformation and the effects of mining stress change,. Utilizing the models of coupling variables, pressure-relief gas migration with coal and rock deformation air-solid coupling model adapting to protective seam mining is established.This paper utilizes COMSOL Multi-physics to carry out numerical simulation of the close-distance lower steep seam protective seam mining binding pressure-relief gas drainage and determine the different mining pressure-relief range, drainage influential radius of different drainage time. The trend drainage radius is larger than the tendency in the same geological conditions and mining conditions.Engineering practices show that gas content of protected seam within the scope of effective protection reduces from the original 6.15 ~ 9.50 m3/t to 2.18 ~ 4.83 m3/t, gas pressure reduces from 0.88 ~ 1.35 MPa to 0.20 ~ 0.35 MPa, and the gas permeability coefficient improves from 0.3541~0.3849m2/(MPa2.d) to 66.0~80.25m2/(MPa2.d),which increase 198 times averagely. Drainage rate of gas reaches 50.93% in the judging region. The inclined upper pressure-relief angle delimits as 86°, the inclined lower pressure-relief angle delimits as 70°, pressure-relief angle of the trend open-off cut delimits as 58°. For the type of protective seam mining, it doesn’t need to construct special bottom rock roadway additionally. The use of inclined gate construction crossing drilling of protective seam working face along gob-side entry retaining can be effective to drainage pressure-relief gas of protected seam and eliminate outburst hazard of protected seam. Protective seam mining is more fully and uniform than hydraulic flushing under the same geological conditions, which proves the importance of protective seam mining in the coal and gas outburst prevention and control once again.Preliminary formed a integral system for guiding the prevention and control of coal and gas outburst, that is, firstly, pre-evaluation of the outburst hazard which based on the gas geology, next is the regional forecast of the outburst hazard, afterward is the feasibility analysis of protective seam mining, and then, for the protective seam mining and pressure relief gas drainage,finally, for the evaluation of drainage standards.Choosing No.1 coal group as protective seam for the mine and Western Henan area,overlying No.2 coal group provides technical parameters and also provides a certain basis for the future regional gas control in Ligou mine and Western Henan area.