Characterization of spatiotemporal distribution of gas in the goaf of W-type ventilated working face

Abstract

In order to solve the problem of gas over limit near the return air trough of W-type ventilated working face, a method combining numerical simulation and on-site measurement was used to study the spatial and temporal distribution characteristics of gas in the goaf under the W-type ventilated mode, and the reliability of the model was verified. Delineate the gas-rich area and suitable pumping area in the goaf, by analyzing the pumping of the top plate high-level directional borehole in the area, optimize the best layout of the top plate high-level directional borehole. The results show: The gas concentration in the goaf gradually increases from shallow to deep in the direction, and increases rapidly in the range of 0–75 m; in the direction of inclination, it is approximately symmetrically distributed along the axis of the return air trough, and gradually decreases toward the air inlets on both sides. The gas concentration in the middle area of the working face is higher than 0.85%; in the vertical direction, the further away from the coal seam roof, the higher the gas concentration, but the growth rate decreases, and the range of high gas concentration gradually expands. The gas concentration of the goaf reflected by the changes in the concentration of the working face has gradually increased in the early stages of mining. and then changes periodically with the cycle of roof pressure in the later stage. There is a strong correlation between the amount of gas emission the goaf and the mining speed of the working face. The regularity of the simulation result is the same as the regularity of the measured results, and the absolute value of the relative error is within 10%, that the concentration of extraction from high-level directional borehole increases with the height of the arrangement, mixed and pure volume decreases with the height of the arrangement. Comparison of the average mixed volume, concentration, pure volume and total extraction volume of each high-level directional borehole, it can be seen that the average pure volume from 3#holes is 3.9 times higher than that from 1#holes, and the total extraction volume accounts for 29% of the total extraction volume from the drill site, it is obtained that the best layout of the high-level directional boreholes of the 3203 working face is between 25 and 35 m above the top board. During the high-level drilling period, the gas concentration in the return air trough was between 0.42% and 0.75%, which effectively prevented the occurrence of gas over limit accidents.