Study On Hydraulic Gas Control Technology Of Roadway Tunneling

It is important to concentrate on gas control during tunneling coal roadway,especially in complicated geographical conditions which contain lots of potential gas accidents and safety factors.Due to frequently gas concentration overrun and times of coal and gas outburst accidents led by blasting,the tunneling speed of coal roadway was as low as 40 meters per month.So it is of significance to research on seam permeability enhancements and effective gas-draining technology which suits this region.It also provide reference and guidance for gas control in similar geographical conditions.This paper firstly get know well about the gas occurrence law about the minable coal seam by field testing.Then analyze the limitation of normal gas pre-draining boreholes and proposes to improve seam permeability by hydraulic methods.Then theoretically analyses the mechanism of seam water injection and high pressure water jet slotting.And puts them into field application,review their outburst control results.At last,verifies the fracture evolution based on hydraulic slotting and the optimal parameters were simulated.The main achievements and results of this paper are as followed.(1)The basic gas parameters of testing area shows that the original gas pressure and gas content is very high and the seam permeability is poor.So it's hard to extract gas from coal seam.No.7 coal seam shows significant coal and gas outburst risk.(2)According to the coal seam features and stress distribution,the normal long holes along seam and penetration hole can't ensure enough coal hole's length.The drilling work is also discordant with roadway tunneling.Due to the extremely low seam permeability and the bottleneck effect,gas drainage meets significant resistance and badly exceeded allowable limit.(3)It reveals the micro-mechanism of eliminating outburst by seam water injection,which is that wet coal has less elasticity but better plasticity than dry coal.It manifests as stress redistribution in macroscopic.According to the effect of seam water injection,the key to prevent coal and gas outburst is to make water wet coal seam uniformly.(4)Research its mechanism from increase of gas emission free surface,the production and development of fractures field,and the formation of distressed zone by means of high pressure water jet slotting.Based on its field application and various indicators during gas draining,point out its superiority to normal gas pre-draining boreholes and seam water injection,and is identified as the most effective means to prevent gas disasters.(5)Simulating the space-time evolution of fractures field and the formation of distressed zone by PFC2 D.It confirms the effective cutting radius as 0.6 meters and the optimal interval between boreholes as 4.8~5.4 meters.The roadway tunneling speed up 50%.It turns out that high pressure water jet slotting could improve permeability of coal seam and prevent gas accidents effectively.