| In recent years, major and extraordinarily-big accidents of gas happened continually. They caused enormous economic loss and bad influences at home and abroad. Among all accidents of coal and gas outburst, accidents happened in soft roof-floor seam occupies an important place, especially in west area of Henan Province, China. In order to avoid and control accidents of coal and gas outburst in three-soft coal seam, theoretical analysis, software numerical simulation, experimental determination, and field observation were used to analyze characteristics of gas parameters in soft roof-floor seam and early-warning model. Early-warning analysis on risk of coal and gas outburst at the coal face of GC Coalmine was carried out by research results. Some conclusions were drawn out in following.According to the Darcy’s law, the laws of conservation of mass and hydrodynamic equations of motion, two partial differential equations about gas flow were established with differential forms. These equations were combined together to solve. Equations of gas pressure field about the radial erratic flow and equation of gas pressure field about ball erratic in coal seam were worked out. Gas pressure was in proportion to r and was inversely proportional to t. Equation of gas flow in unit area from a circle which radius was r and equation of coal seam permeability coefficient λ were deduced in line with equation of gas pressure field and Darcy’s law. Gas flow and coal seam permeability coefficient both are functions about time t and distance r from the center of borehole or tunnel.The initial velocity of gas emission, front abutment pressure at coal face, gas mission and permeability coefficient in coal seam, et al, were analyzed by the theoretical analysis and numerical simulation. The results show that there are similar or opposite variation regularity among these parameters, which are the combinations of S-shaped curve and inverted S-shaped curve associated to the distance x or time t. Meanwhile, permeability coefficient curve with distance, as well as gas pressure and abutment pressure with distance, all present not exactly symmetrical characteristics. Thus, the variation regularity of parameters can be determined with specific coal mine conditions. The research results can provide theoretical guidance to the prevention and control of gas disaster in coal mines.Equations of gas flow in 2-dimension and 3–dimension spheroid were derived from theoretical analysis and numerical simulation. Process of coal and gas outburst can be explained by means of equation of gas flow.Risk of coal and gas outburst in three-soft coal seam was analyzed with Fault Tree Analysis. Probability of occurrence of outburst accident was ascertained. Possible ways to cause outburst accident and to avoid outburst accident were worked out. The order preferences of all elementary events to cause outburst accident were determined.Early-warning indices system of coal and gas outburst in soft roof-floor seam was constructed. There were 8 indices in all, such as gas pressure, et al. Weights of all early-warning indices were determined by Analytic Hierarchy Process. On the same time, weights of all early-warning indices were calculated based on critical important degree of elementary events in FTA. Comprehensive weights of early-warning indices could be calculated by the above two kinds of weights.Based on extension theory and comprehensive weights, extensible early-warning model was built. It was used to analyze risk of coal and gas outburst at coal face 12041 in GC Coal Mine. The result of early-warning analysis is general possibility. |
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