# Permeability Enhancement Induced by Fracture Shear Dilation During Close-Range Coal Seam Mining
## 5 Discussion  
### Design Parameter of High-Level Suction Roadway  
Understanding the evolution and distribution of the mining-induced fractures in the overlying strata helps select the position of high drainage roadways. The application of the high suction roadway is to extricate more goat gas of high concentration and reduce gas emission quantity at the upper corner during mining activities.  
Based on a quantitative analysis of the gas source during the mining of coal seam 8#, the gas source in the overlying coal seam accounted for more than 30% of the total gas emission. Therefore, it was necessary to arrange a high-level drainage path to direct the gas flow from the overlying coal seam to the goat. Combined with the above numerical simulation, the design scheme of the high-level suction roadway is described as follows:  
1. From the beginning of the open-off cut, the movement law of the overlying strata in the initial mining stage was considered. Within 65 m of the advancing length along the working face, the high suction roadway should be 25 m in the wrong return air roadway, and the vertical distance from the coal seam increased from 12 to 15 m. After mining was completed, the high-level suction roadway could achieve a good drainage effect in a short time.
2. When the working face length was within the range of 65-110 m, the high-level suction roadway should not be too high and should be arranged in the middle and lower parts of the fracture zone as much as possible. In this case, the vertical distance between the high-level suction roadway and the coal seam increased from 15 to 25 m. The horizontal distance of the inclined working face boundary in the high-level suction roadway was 25 m.
3. When the advancing distance of the working face was within the range of 110-180 m, the high-level suction roadway could be appropriately raised. At this time, the horizontal distance of the inclined working face boundary in the high-level suction roadway was set to 25 m, and the vertical distance between the high-level suction roadway and the coal seam increased from 25 to 35 m.
4. When the advancing distance of the working face was greater than 180 m, the fracture zone was fully developed. At this time, the horizontal distance of the inclined working face boundary in the high-level suction roadway was 25 m, and the vertical distance between the high-level suction roadway and the coal seam was approximately 35 m.
5. The main body of the high-level suction roadway was located in the middle and upper parts of the fracture zone formed by mining in coal seam 8#, and the gas drainage had a wide influence range. The height of the high-level suction roadway was arranged on the basis of different working face mining degrees, in such a way to ensure that the high-level suction roadway was connected to the O-shaped circle formed by working face mining earlier and that the drainage influence range was wide. This measure could effectively cut off the gas influx into the mining space in the entire goat and surrounding coal-rock mass and allow for effective drainage in the goat and surrounding coal-rock mass.