Determining the optimal extrication location of the high extraction roadway can improve the gas extrication effect of highly gassy mine and solve the problem of gas concentration overrun at the upper corner, which is of great significance to safety and efficient mine production. According to the actual situation of mine, the gas gushing amount in the goaf, pressure difference at both ends of the working face, the 3D porosity, and permeability distribution of the caving zone and fissure zone were obtained by field measurement and numerical calculation. Through theoretical calculation, the proper extraction site of a high-position alley was determined. On this basis, the optimal extraction site of a high-position alley was determined by numerical analysis of the gas extraction effect at different sites. The results show that as the perpendicular distance between high-position alley and goaf floor increases, the gas extraction amount increases first and then decreases. The concentration of extraction gas gradually increases, and the increasing trend is gradually diminished. With the increase of the horizontal distance between the air return way and the high-position alley, the gas extraction amount and gas extraction concentration increase first and then decrease. The optimal extraction site of a high-position alley should be 39 m vertically away from the goaf floor and 30 m horizontally away from the air return way.
Gas disaster has long been a key factor threatening safety mine production of China; in particular, the gas in goaf severely affects the safety condition of coal face [
To determine the optimal extrication location of the high suction roadway, researches have conducted large amounts of researches [
9101 working face is located at the north of the Xiandu agricultural ecological garden of the Xinming village. In the mine, the east of 9101 workface is 81/2# pulley roadway, the west of 9101 workface is 3D seismic prospecting fault, the south of 9101 workface is 9102 design working face, and the north of 9101 workface connects Jiang river coal pillar. The ground elevation at the site where 9101 workface is located is 903 m∼917 m, and the workface elevation is 285 m∼525 m. The workface is arranged along the coal seam, with a slope length of 335 m, transport roadway length of 1404 m, wind roadway length of 1657 m, and U-shaped ventilation. The thickness of the coal seam is 5.85 m, and mean obliquity of the coal seam is 10°C, which indicates it is a gently inclined coal seam, with medium-hard overburden rocks. The all-roof caving method is adopted as the roof control method.
Assume that the stope fluid is the incompressible fluid, goaf is the isotropous porous medium, and goaf gas flow is in line with the linear permeation law, i.e., Darcy’s law [
Mass conservation equation:
Navier–Stokes equation:
Composition transfer equation:
The standard
According to the empirical equation, the model can calculate the height range of the caving zone as 17.55∼23.4 m and the height range of the fissure zone as 49.48∼60.68 m. For the convenience of model establishment and mesh generation, the height of the goaf physical model was determined as 60 m. The dimensions of the workface, goaf, and high suction roadway (arranged along the goaf, located within the fissure zone of roof damage, interiorly dislocated with the air return roadway by certain distance, and supported by the bolting net) were determined according to the actual situation, as shown in Table
Dimension of the 9101 workface physical model.
Dimension | Name | ||
---|---|---|---|
Length (m) | Width (m) | Height (m) | |
Workface | 335 | 5 | 5 |
Goaf | 300 | 335 | 60 |
High suction roadway | 290 | 4.5 | 3 |
Inlet and return air roadway | 30 | 5 | 4.5 |
Given that the maximum height of the caving zone of 9101 workface is 23.4 m and the maximum height of the fissure zone is 60.68 m, the high suction roadway will be easily deformed and losing extrication ability if the arrangement height of the high suction roadway is less than 23.4 m; if the distance between the high suction roadway and the goaf floor is too large, the gas permeability of the overlying rock will be poor, and the extrication amount of gas will be less. Therefore, the 5 high suction roadways are set 30 m horizontally away from the return air roadway, and vertically high above the goaf floor by 25 m, 32 m, 39 m, 46 m, and 53 m, respectively.
Given that the goaf boundary abscission rate of the high suction roadway side close to the return air roadway was low, no large amounts of channels are formed for gas transport; when the horizontal distance between the high suction roadway and the return air roadway is too large, the goaf caving rocks will be gradually compacted, the abscission rate will be reduced, and goaf gas concentration will be decreased also. Therefore, the 5 high suction roadways are set 39 m vertically high above the goaf floor, and horizontally away from the return air roadway by 20 m, 30 m, 40 m, 50 m, and 60 m, respectively.
Based on the physical model dimension of the workface and the location arrangement parameters of the high suction roadway, it can determine the workface physical model under the high suction roadway extrication condition, as shown in Figure
Goaf physical model of fully mechanized face.
According to the gas emission quantity of Wangzhuang mine 9101 workface during the period of stoping, as well as the goaf permeability distribution law and field test data, the model boundary conditions can be set as follows: The inlet of the inlet air roadway is the velocity-inlet, with a mean air speed of 2.59 m/s. The outlet of the return air roadway is the pressure-outlet, with a differential pressure of −130 Pa; the outlet of the high suction roadway is the pressure-outlet, with a negative extrication pressure set as −13 kPa. Goaf gas is emitted from the floor, lower neighboring coal seam, and surrounding rock, wherein the gas emission quantity is predicted as 28.33 m3/min using a different-source forecast method. Goaf permeability: analyze the overlying rock property, mining method, and support form of Wangzhuang mine 9101 workface. Simulate the deformation condition of the goaf overlying rock using UDEC numerical simulation software. Conduct comparative analysis of deflections of rock stratums. The 3D porosity distribution laws of the caving zone and the fissure zone of Wangzhuang mine 9101 workface can be obtained according to the porosity calculation equation (as shown by Formulas (
The vertical distance between the high suction roadway and the goaf floor is related to the mining method, overlying rock property, and coal bed pitch. According to Table
Moderate arrangement height of the high suction roadway.
Coal bed pitch | Overlying rock hardness | Roof management method | Ratio of moderate arrangement height and mining height ( |
---|---|---|---|
Gentle dip | Hard | All roof caving | 6∼18 |
Gentle dip | Medium hard | All roof caving | 5∼12 |
Gentle dip | Soft | All roof caving | 3∼9 |
Gentle dip | Weathering soft | All roof caving | 2∼7 |
Moderate dip | Medium hard | All roof caving | 5∼12 |
Steep dip | Hard | All roof caving | 7∼16 |
Steep dip | Medium hard | All roof caving | 5∼6 |
Steep dip | Medium hard | Filling | — |
As shown in Table
Based on the reasonable physical model and boundary conditions, the gas extrication effect was simulated using Fluent software under constant horizontal distance between the high suction roadway and the return air roadway, and the vertical distance between the high suction roadway and the goaf floor is 25 m, 32 m, 39 m, 46 m, and 53 m, respectively. The concentration and scalar of the extricated gas are shown in Figure
Extrication effect under different vertical distances between the high extraction roadway and the goaf floor.
Through analyzing Figure
In setting the distance between the high suction roadway and the return air roadway, i.e., horizontal projection distance, the high suction roadway should be located within the fissure zone after sufficient pressure relief, and also the high suction roadway should not be damaged. In addition, the horizontal projection distance should not exceed 1/3 of the stope face length, as shown in Figure
Profile perspective drawing of high suction roadway arrangement.
Using the above equations, it can be calculated that the vertical distance between the high suction roadway and the goaf floor is 39 m, the horizontal projection length
Based on the reasonable physical model and boundary conditions, the gas extrication effect was simulated using Fluent software under constant vertical distance between the high suction roadway and the goaf floor, and the horizontal distance between the high suction roadway and the goaf floor is 20 m, 30 m, 40 m, 50 m, and 60m, respectively. The concentration and scalar of the extricated gas are shown in Figure
Extrication effect of the high extraction roadway under different horizontal distances between the high extraction roadway and the return air roadway.
Through analyzing Figure
The high extraction roadway of Wangzhuang mine 9101 workface was laid out according to the data. Gas drainage data of the high extraction roadway were monitored in June 2013. The gas extraction concentration is 11.4%∼13%, and the average value is 12.28%; the average gas concentration in the upper corner is 0.69%. Therefore, the field test results are in good agreement with the numerical simulation results. It also verifies the correctness of the numerical simulation method and results.
The scalar of gas extricated by the high suction roadway first increases and then decreases with the increase of the vertical distance between the high suction roadway and the goaf floor and reaches its maximum value of 16.74 m3/min when the vertical distance is 39 m; the concentration of the extricated gas is gradually increasing; however, the increasing trend will be significantly decreased after the vertical distance between the high suction roadway and the goaf floor is larger than 39 m. Both scalar and concentration of the gas extricated by the high suction roadway first increase and then decrease with the increase of the horizontal distance between the high suction roadway and the goaf floor and reach their maximum values of 16.74 m3/min and 13.20% when the horizontal distance is 30 m. Combining the theoretical calculation results and numerical simulation results, it can be concluded that the optimal extrication location for the high suction roadway of Wangzhuang mine 9101 workface is vertically 39 m above from the goaf floor and horizontally 30 m away from the return air roadway.
The data used to support the findings of this study are available from the corresponding author upon request.
The authors declare that they have no conflicts of interest.
This work was supported by the National Natural Science Foundation of China (Grant nos. 51734007, 51704099, and 51604101), the Henan Province Basic and Frontier Technology Research Projects of China (Grant No. 142300413233), Key Scientific Research Projects in Colleges and Universities in Henan (Grant No. 19A440003), and the Opening Foundation of State Key Laboratory Cultivation Base for Gas Geology and Gas Control (Grant No. WS2017B14).