Technic Study On Increasing Permeability Of Deep-hole Presplitting Blasting And Its Application In Low Permeability Coal Seam

In the process of coal mining, gas hazard is always one of the main hazards which threat safety mining production in coal mine. Domestic and foreign scholars had done lots of work on controlling gas hazards and accomplished some achievements, but still can not completely avoid gas disasters fundamentally. At present, measures of pumping and extracting gas from coal seams are considered as one of effective methods controlling gas hazard. But as the increasing of mining depth, gas pressure and amount are becoming higher, permeability of coal seams becoming lower. These limited the rate of pumping and extracting gas and its effect severely. Therefore, increasing permeability of low permeable coal seams is a method to increase gas pumping and extracting rate to make mining production safe and improve efficiency. Most of coal field in our country are coal seams of low permeable and high gas occurrence, developing study on pressure relief and increasing permeability of coal seams to pump and extract gas of low permeable and high gas occurrence coal seams has important social value and economic benefit especially on preventing coal and gas outburst.On the basic of forerunner' achievements, this paper researched deep-hole presplitting blast technology and its mechanism of preventing coal and gas outburst by applying theoretical analysis,experimental study,numerical simulation and test on workplaces. Coal body structure and pore characteristics are analyzed at first, and get the result that the huge network caused by pore and fracture is the channel of gas migration, and the amount of gas migration is closely related to permeability and mechanical performance of coal and rock. Studying on gas flow theory of coal seams provided a powerful basis to find effective measures controlling gas of low permeable and high gas occurrence coal seams and avoid occurrence of gas disaster. Secondly this paper researched deep-hole presplitting blast technology and its mechanism on low permeable and high gas occurrence coal seams. By analyzing, author get that explosive stress wave and explosive gas are the main factor to make coal medium's fracture, and make a lot of fracture network by blasting hole. Controlling bores provide lots of auxiliary free surface to blasting holes, enlarged the range of fracture area. The research also showed that gas pressure of coal seams play a active role on enlarging of fracture area; this paper comprehensively analyzed the pressure relief and increasing permeability of coal seams mechanism of deep-hole presplitting and controlling blast, it shows that the technology increased the coal fracture and permeability of coal seams, redistribution of stress, beneficial to gas pumping and extracting of gas in coal seams, lower the gas amount and the gas pressure in coal body, so as to eliminate and prevent gas disaster. This research also selected equal explosive pipe, and test the performance by experiments. The result shows that the explosive pipe is low speed,flame retardant,antistatic and waterproof. Its performance of detonation transmission is reliable. Simulation experiment of explosive pipe explosion loosening effect in mediums was also done. It shows that the loosening effect is obvious in soil,coal and rock, loosening radius of soil and coal is about 4m, and it is more than 2m in rock, its detonation transmission distance is over 50m, so the explosive gave a good effect on increasing permeability of low permealility coal seams. This paper also established different holes arrangement mathematical models of low permeability high gas occurrence deep-hole presplitting blast. A numerical simulation was carried on by the software of Ansys/Ls-Dyna. It shows that when the distance between two blasting holes is 6~7m, coal body between two holes would generate enough throughout fractures, at this time ground stress on coal body is small than the initial ground stress, pressure on coal body are relived, permeability of coal is increased, channel for pumping and extracting gas are provided.Those research results above are applied on fully-mechanized face with the permeable and high gas occurrence,rock cross-cut coal uncovering and heading face. Blasting to relive ground stress and increase permeability in these workplace, and massive high-concentration gas was pumped and extracted. It shows the results providing some effective technical method for efficient and safe mining.