The Theory And Its Application On Coal Mining And Gas Extraction In Outburst Coal Seams Of Steeply

Due to the large inclination, there are problems called as "three small five big" in the steeply inclining outburst coal seam group mining, such as small coal mine, low mine pressure, low recovery rate, gas control difficulty, high drivage rate of roadway, large influenced range, high consumption for every tons of coal and high labor intensity. How to carry out extracting coal and gas in this kind of coal seam is a difficult technical problem. According to the requirements of "coal and gas outburst prevention regulations", in the exploitation of such coal, what should be solved is the problem of gas before and after the coal seam is mined, and after that the coal can be mined. This is requirement for single outburst coal seam mining. As for the mining of coal seam, the gas in adjacent seams should be treated additionally. As a clean energy, gas can not be simply extracted and it should be actively utilized. Therefore, in the project of " Study on the Common Mining Theory of Steeply Coal Seams and Gas", through experiments, theoretical analysis, numerical simulation and field tests, systematic studies have been done on the mining pressure of steep coal seam group and its influence to gas, the theory on gas pressure relief and outburst elimination, collaborative mining method of coal and gas, the selection of protection lay, the migration law of gas in the mining process and its control technology, and a series of achievements have been made, which ensure high yield, efficiency and safety in the mining process of steep coal and gas outburst coal seams.1) Study on the theory about gas pressure relief and outburst elimination. Although the permeability coefficient of outburst coal is low, once the coal seam is loose, the permeability coefficient will be increased hundreds times, as a result, the gas pressure will be reduced while its emergence rate is increased, and the danger of coal and gas outburst will also be reduces and even eliminated. According to the law of gas migration and surrounding rock broken, the theory " Cutting-Pumping-Digging-Mining" for gas pressure relief and outburst elimination has been put forward:making the coal cracking and loose by cutting the coal seam to promote the transformation of gas from adsorption state to flow state, and then to extract gas to meet the requirement of relieving gas pressure and eliminating the danger of gas outburst before the roadway is constructed. In the process of tunneling and mining, the law of mine pressure redistribution is used to release the gas pressure of protected seam in the area of protective layer mining so that the gas in high place is drained and the gas pressure relief and coal outburst elimination in the process of mining and after mining has been achieved.2) Study on the theory of gas migration. Careful analysis on the role of coal rock pore, fissure in gas transportation process has been made., and a fluid-solid coupling model of considering the effect of coal rock and its constitutive relation has been put forward, and the solid-liquid coupling tests of coal mass have been conducted. The results show that in the coal and rock mass through cracks, gas migration is fast; gas migration in pore of coal and rock lags behind that in fissure coal and rock. The time evolution law that the pore unit effective volume stress and fracture unit effective normal stress develop with the seepage has been revealed.3) Study on the theory of roof caving zone and fractured zone in steeply inclining outburst coal seam group mining. Based on the pressure relief theory, the "three vertical mining face" has been tested and simulated. Through water injection test, the height of caving zone and fractured zone in working face has been measured. It is showed that the height of caving zone is4?8times of the height of working face, the height of fracture zone is6-10times of that. The caving zone and fractured zone have a tendency of shifting to the return airflow roadway above. The vertical three-zone in inclined coal seams is different from that of gently inclined seam, which provides a theoretical basis for the mining of outburst coal seam group.4) Study on the new forecasting techniques of the gas emission quantity from working face. Based on the uncertainty measurement theory, the mean attribute measure clustering model for coal face gas emission prediction is established. In this model, the sample mean is set as the cluster center, the weight index of evaluation parameters are determine by the mean of entropy. Through calculating the sum of the product of sample entropy weight comprehensive measure and target mean of classification that the sample belonged, the gas emission prediction value is obtained. The analysis of examples indicates that the error between predicted values and the measured values is small. As the modeling process is simple, the model is practical in engineering.5) Study on the protective coal seam mining technology in the steeply inclining outburst coal seam group. The first step on mining inclined outburst coal seam group is the mining of protective coal seam. Taking Shexingshan Coal Mine as an example, through technical and economic comparison, the down protective layer is chosen to be exploited. The results of field tests and numerical analysis show that after the down protective layer has been mined the moving angle of upper stope decrease, while the moving angle of lower stope increase, the moving angle along the left and right boundary also decrease, which provides the theoretical basis for protection layer mining in the future.6) Study on the theory of together mining of coal and gas. Based on the study of gas extraction in elevated lane, the coal and gas exploitation theory and technology have been proposed firstly, and a field experiment has been conducted. The results show that the construction technology is simple, quick and easy to master for workers and the concentration and the scalar of gas has been improved significantly, which solve the overrun problem of gas in the mining process of protective layer, but also provide a new way for the gas extraction of protected layer.7) Study on the mechanism of gas in protective layer while the protective layer is being mined. The mining of protected layer is closely related to gas pressure. Through the FLAC3D, the numerical analysis is carried out on protected layer mining while the protected layer with different gas pressure. It is shown that the increase of gas pressure can accelerate the fracture of protection layer roof, especially when the gas pressure of protected layer is higher than2MPa, the fracture of protective layer roof is exacerbated, and even serious outburst is caused. So it is required that in the process of protective layer mining, the gas drainage of protective layer should be strengthened to reduce the harm of high gas pressure to the mining of protection layer.