1.Gas Research Branch, China Coal Technology Engineering Group Chongqing Research Institute, Chongqing ,China；2.National Key Laboratory of Gas Disaster Detecting, Preventing and Emergency Controlling, China Coal Technology Engineering Group Chongqing Research Institute, Chongqing , China

In order to effectively solve the problem of low pre-draining efficiency of the gas area of the coal roadway in Dingji Coal Mine with high ground stress and low permeability, the regional verification index still exceeds the standard after the pre-drainage meets the standard. Drilling holes were used to study the application of pressure relief and anti-reflection technology for ultra-high pressure hydraulic slits. The principle of pressure relief and anti-reflection enhancement of hydraulic slotting and the composition of ultra-high pressure hydraulic slotting equipment were summarized. Ultra-high pressure water-cleaning pumps, ultra-high pressure hoses, ultra-high pressure rotary tail, hydraulic slotting drill pipe, high and low pressure switching slotting device, drill bit and ultra-high pressure remote operation table and other ultra-high pressure hydraulic slotting equipment were selected and matched, the natural gas emission from uncut drilling and slotted drilling with the same borehole diameter and gas extraction from slotted drilling were investigated. The initial gas emission and gas emission attenuation coefficient, and the effective extraction radius under different conditions of pre-drainage time and pre-drainage rate conditions were studied theoretically.The effect of gas outburst prevention measures in the pre-drainage of gas unit of the bedding layer and hydraulic slotting by drilling through the seam were tested on site, the implementation of partial supplementary measures and effect of partial measures of pre-extraction unit with different measures were counted. The situation and the effects of local measures were analyzed and evaluated for the effect of pressure relief and permeability enhancement of ultra-high pressure hydraulic slits. The results show that the parameters of ultra-high pressure hydraulic slotting equipment matched the type selection of No.11-2 coal seam engineering conditions in Dingji Coal Mine were reasonable, the effect of pressure relief and permeability enhancement by ultra-high pressure hydraulic slotting in cross-layer boreholes of No.11-2 coal seam in 1351 (1) coal roadway along transport channel was remarkable. Compared with the non-permeability-increasing measures, the permeability coefficient of the coal seam was increased by 25.9 times, the amount of gas emission from a hundred meter coal hole through a 113 mm hole increased by 5.5 times,the gas emission attenuation coefficient was decreased by 73.4%, and the distance between boreholes with 35% pre-drainage rate after 15 and 30 days of pre-drainage were increased by 84.3% and 53.0%. Compared with the hydraulic punching of the through-hole drilling,the local supplementary measures of coal roadway strips after ultra-high pressure hydraulic cutting was reduced by 50.0%, and the average driving speed of coal roadway was doubled.