Simulation Experiment On The Mechanical Characteristics During Outbursting Coal Seam Uncovered By Crosscut

Coal and gas outburst of coal seam uncovered by crosscut is an extremely complex dynamic disaster in the coal mining, its intensity is often biggest in all kinds of outbursts and its hazardness is extremely high. Statistics indicates that 80% of the serious coal and gas outbursts occur in coal uncovering by crosscut. Therefore, study of outburst mechanism of the gaseous coal (rock) uncovered by crosscut has vital practical significances for guaranteeing the safe and highly effective production in coal mine. It is known to all, coal and gas outburst is a complex mechanical problem that occurs under special conditions, for example, crustal stress, gas pressure, coal structure and strength, and so on. According to the statistical data, as other kinds of outbursts, the outburst occur in coal seam uncovered by crosscut has some relation with the tectonic zone. But up to present, very few people have studied the mechanical characteristics of the surrounding rock during coal seam unvovering and the outburst characteristics systematically.Bases on the theories of the rock mechanics, the geognosy, the gas storage and flowing, and coal and gas outburst mechanism, and so on, the author defines the concept of "tectonic mass" after summarizing the characters of the rupture zones due to some kinds of geological structures. Taking the rupture zone in coal seam created by the reversed fault structure as the model, the author proposes the outburst model for "tectonic mass" containing coal seam uncovered by crosscut, and carries on preliminary analysis of mechanical and energy binding characteristics of the model, then, analyzes the coal and the gas outburst mechanism of the model.According to the distribution of layers and the coal (rock) mechanical characteristic around of C13-1 coal seam in Huainan, the author sets up experiment apparatus system for coal and gas outburst in the laboratory and carries on the similar material experiment of coal seam uncovered by crosscut in the apparatus. It studies the mechanical characteristics of the surrounding rock and the outburst characteristics of the "tectonic mass" containing coal seam, including:crustal stress evolution, the distortion and displacement, the change of gas pressure and temperature in the "tectonic mass" and coal seam when gasification and outburst starting. The findings are as follows:Firstly, because of the friction force between the model material and the wall of the apparatus, the menstruated stress around the apparatus wall is evidently lower. Secondly, as the workface of crosscut advancing to the "tectonic mass", obvious stress concentration exits in the front surrounding rock. Thirdly, in the process of advancing distortion and displacement exit in the upper surrounding rock, the biggest displacement, for good support laneway is 3mm (12cm if in the mine field), but when outburst takes place, the displacement of the "tectonic mass" surrounding rock surpasses 50mm (2.0m if in the field). Fourthly, when inflating gas, the increasing range and velocity of the temperature of the "tectonic mass" are larger and faster than that of the coal seam. Fifthly, after the outburst, the volume of the outburst cavity becomes 20% smaller than before.Combined with the laboratory similar material simulation, the author founds corresponding numerical model with the rock breaking solid-gas coupling software RFPA2D-Flow. It analyzes the evolution process of the crustal stress field, the AE, the gas flow field and the gas pressure field of the surrounding rock during the coal seam uncovered by the crosscut, and reappears the outburst of the "tectonic mass" containing coal seam uncovered by crosscut from a microscopic view.The simulating results are in substance coincident with that of the similar material experiment. Bsides, through changing stress and coal strength, it founds some other rules as follows:fitstly, besides increasing deformation of the surrounding rock, the high crustal stress may break the tectonic material further, and is helpful in forming large-scale outburst; secondly, for low stress situation, outburst coal is often limited to the scope of the "tectonic mass", the outburst intensity reduces relatively; thirdly, on the condition of high crustal stress and gas pressure, enhancing the mechanical properties of the "tectonic mass", the outburst is not easy to occur, only exits some rupture.Finally, the author gives some field cases of coal and gas outburst in coalseams which contain "tectonic mass" to approve the objective existence of the influence from the "tectonic mass".The author also explains the reason of these gas disasters with the discussion of the experiment studies.Through the theoretical analysis, similar experimental and the numerical simulation analysis, it obtains the reason for the outburst in uncovered coal seam containing "tectonic mass":because of the structure stress field, the virgin stress is high in "tectonic mass" zone; With tunnel advancing, the stress of the surrouding rock furtherly increases, the formation distortion is small, the gas pressure is high. Even when the workface is near to the "tectonic mass" zone, they are still very high; When the caving workface opens the "tectonic mss" suddenly, the outburst occurs instantaneously, then, the crustal stress and the gas pressure rapidly reduce. Obviously, in the process of the tunnel advancing, the outbursting coal seam which contians the "tectonic mass" has been maintaining high crustal stress and bearing pressure are the reason for the outburst. The research has certain theoretical instruction and practical profit significance to furtherly understanding the mechanism of the outburst in coal seam affected by complex geological structure and outburst disaster prevention.