This paper analyzes the control mechanism of coal and gas outbursts and proposes the concept of an effective pressure relief protection range, based on the stress relief of the underlying coal-rock mass and the develo...This paper analyzes the control mechanism of coal and gas outbursts and proposes the concept of an effective pressure relief protection range, based on the stress relief of the underlying coal-rock mass and the development of a plastic zone. Also this study developed a stress change and fracture development model of the underlying coal-rock mass. In addition, the stress and depth of fracture of any point in the floor were deduced with the application of Maple Calculation Software. The specific engineering parameters of the Pingdingshan No. 12 colliery were applied to determine the relationship between the depth of fracture in the floor and the mining height. The pressure-relief principle of the underlying coal-rock mass was analyzed while varying the mining height of the upper protective seam. The findings indicate that as the depth of fracture in the floor increases, the underlying coal-rock mass experiences a limited amount of pressure relief, and the pressure relief protection range becomes narrower.Additionally, the stress distribution evolves from a ‘‘U" shape into a ‘‘V" shape. A 2.0 m mining height of protective seam situates the outburst-prone seam, Ji_(15), within the effective pressure relief protection range. The fracture development and stress-relief ratio rises to 88%, ensuring the pressure-relief effect as well as economic benefits. The measurement data show that: after mining the upper protective seam, the gas pressure of Ji_(15) dropped from 1.78 to 0.35 MPa, demonstrating agreement between the engineering application and the theoretical calculation.展开更多
Fences are one of the most effective measures to prevent and control wind-blown sand disasters,and the blocking effect of fences is largely determined by their porosity and height(H).This study employed wind tunnel ex...Fences are one of the most effective measures to prevent and control wind-blown sand disasters,and the blocking effect of fences is largely determined by their porosity and height(H).This study employed wind tunnel experiments to measure wind velocities on both sides of wire mesh sand fences with porosities of 75%,63%,56%,36%and heights of 10,5 and 2 cm.The effects of porosity and height on the blocking effect of the fences were evaluated on the basis of velocity variability,flow field,and the wind velocity reduction coefficient.Results show that the smaller the porosity,the stronger the blocking effect.The fence with a porosity of 36%had the strongest windproof efficiency of 0.70 and longest protection range of 9 H,and thus showed the best applicability in preventing and controlling wind-blown sand disasters.The fence with a porosity of 56%showed a windproof efficiency of 0.31 and a protection range of 7 H,which could be considered for adoption.However,fences with porosities of 75%and 63%were not recommended to be adopted,because their windproof efficiency and protection range were very small.Overall,the higher the fence,the stronger the blocking effect.The highest fence(10 cm)had the longest protection range of 90 cm,which was the best in application.Nevertheless,the 5 and 2 cm fences were almost consistent with 10 cm fence in windproof efficiency,which was still suitable for wind and sand fixation.展开更多
China is the country most seriously affected by coal and gas outburst accidents, which not only has the largest number of outburst mines, but also has a large number of outburst times and intensity. China's annual...China is the country most seriously affected by coal and gas outburst accidents, which not only has the largest number of outburst mines, but also has a large number of outburst times and intensity. China's annual total number of outburst and average intensity of outburst are far higher than the average level of major coal-producing countries in the world. In order to prevent coal and gas outburst accidents, China actively adopts coal mine outburst prevention measures, but the coal mine outburst prevention cost in China is as high as 50-60 yuan /t, which brings great economic pressure to coal mines. During coal seam mining and roadway excavation, on the one hand, when the mining work destroys or disturbs the original gas balance state in the stratum, the high gas in the coal seam will desorb and drift to the space with lower air pressure, and enter the goaf;On the other hand, mining causes the stress redistribution of surrounding rock in stope and changes the structure of coal and rock mass, and then changes the accumulation mode and migration form of gas in coal and rock mass, forming a certain width of outburst elimination area. In order to reduce the cost of outburst prevention and make rational use of outburst elimination belt, many coal and gas outburst mines in China adopt gob-side entry driving. However, the protection effect and scope of mined-out areas to surrounding solid coal are still unclear, and the Detailed Rules for Prevention and Control of Coal and Gas Outburst requires that mining activities in coal seams must take measures to eliminate outburst danger. Therefore, it is urgent to scientifically investigate and study the scope of pressure relief protection in solid coal along the gob side, so as to provide scientific basis and technical support for driving along the gob side, improve the utilization rate of resources, ensure safety in production, and have good economic and social benefits.展开更多
基金supported by the Foundation for Distinguished professor of Jiangsu Provincethe Foundation for Innovative Research Groups of the National Natural Science Foundation of China (No.51421003)
文摘This paper analyzes the control mechanism of coal and gas outbursts and proposes the concept of an effective pressure relief protection range, based on the stress relief of the underlying coal-rock mass and the development of a plastic zone. Also this study developed a stress change and fracture development model of the underlying coal-rock mass. In addition, the stress and depth of fracture of any point in the floor were deduced with the application of Maple Calculation Software. The specific engineering parameters of the Pingdingshan No. 12 colliery were applied to determine the relationship between the depth of fracture in the floor and the mining height. The pressure-relief principle of the underlying coal-rock mass was analyzed while varying the mining height of the upper protective seam. The findings indicate that as the depth of fracture in the floor increases, the underlying coal-rock mass experiences a limited amount of pressure relief, and the pressure relief protection range becomes narrower.Additionally, the stress distribution evolves from a ‘‘U" shape into a ‘‘V" shape. A 2.0 m mining height of protective seam situates the outburst-prone seam, Ji_(15), within the effective pressure relief protection range. The fracture development and stress-relief ratio rises to 88%, ensuring the pressure-relief effect as well as economic benefits. The measurement data show that: after mining the upper protective seam, the gas pressure of Ji_(15) dropped from 1.78 to 0.35 MPa, demonstrating agreement between the engineering application and the theoretical calculation.
基金supported by the National Natural Sciences Foundation of China(41871016)。
文摘Fences are one of the most effective measures to prevent and control wind-blown sand disasters,and the blocking effect of fences is largely determined by their porosity and height(H).This study employed wind tunnel experiments to measure wind velocities on both sides of wire mesh sand fences with porosities of 75%,63%,56%,36%and heights of 10,5 and 2 cm.The effects of porosity and height on the blocking effect of the fences were evaluated on the basis of velocity variability,flow field,and the wind velocity reduction coefficient.Results show that the smaller the porosity,the stronger the blocking effect.The fence with a porosity of 36%had the strongest windproof efficiency of 0.70 and longest protection range of 9 H,and thus showed the best applicability in preventing and controlling wind-blown sand disasters.The fence with a porosity of 56%showed a windproof efficiency of 0.31 and a protection range of 7 H,which could be considered for adoption.However,fences with porosities of 75%and 63%were not recommended to be adopted,because their windproof efficiency and protection range were very small.Overall,the higher the fence,the stronger the blocking effect.The highest fence(10 cm)had the longest protection range of 90 cm,which was the best in application.Nevertheless,the 5 and 2 cm fences were almost consistent with 10 cm fence in windproof efficiency,which was still suitable for wind and sand fixation.
文摘China is the country most seriously affected by coal and gas outburst accidents, which not only has the largest number of outburst mines, but also has a large number of outburst times and intensity. China's annual total number of outburst and average intensity of outburst are far higher than the average level of major coal-producing countries in the world. In order to prevent coal and gas outburst accidents, China actively adopts coal mine outburst prevention measures, but the coal mine outburst prevention cost in China is as high as 50-60 yuan /t, which brings great economic pressure to coal mines. During coal seam mining and roadway excavation, on the one hand, when the mining work destroys or disturbs the original gas balance state in the stratum, the high gas in the coal seam will desorb and drift to the space with lower air pressure, and enter the goaf;On the other hand, mining causes the stress redistribution of surrounding rock in stope and changes the structure of coal and rock mass, and then changes the accumulation mode and migration form of gas in coal and rock mass, forming a certain width of outburst elimination area. In order to reduce the cost of outburst prevention and make rational use of outburst elimination belt, many coal and gas outburst mines in China adopt gob-side entry driving. However, the protection effect and scope of mined-out areas to surrounding solid coal are still unclear, and the Detailed Rules for Prevention and Control of Coal and Gas Outburst requires that mining activities in coal seams must take measures to eliminate outburst danger. Therefore, it is urgent to scientifically investigate and study the scope of pressure relief protection in solid coal along the gob side, so as to provide scientific basis and technical support for driving along the gob side, improve the utilization rate of resources, ensure safety in production, and have good economic and social benefits.
