Abstract
Because gas boreholes are easy to damage by integrated coal mining and gas exploration, based on the practice of relieving pressure in deep thin coal seams in the Huainan mining area, a multidimensional coupling numerical simulation method was used to reveal the space‐time evolution characteristics and influence factors of fracture deformation of gob‐side gas boreholes. Results indicate that the danger zone for borehole fractures is primarily between 5 and 12 m above the roof of the roadway. The final‐hole position has little effect on the stability of boreholes, and migrating the open‐hole position to the entity coal side and roadway roof side can improve the stability of the borehole. The initial failure of the borehole occurs at a distance of 10 m behind the coal face. The failure of the borehole is largely stable at a distance of 100 to 120 m behind the coal face. With the increase in mining height, which leads to an increase in the movement of strata and an increase in pressure relief range, the shear stability of the borehole is reduced, and the extrusion stability of the borehole is improved. A hard roof condition promotes borehole shear stability, while a weak roof condition promotes borehole extrusion stability. This change can decrease the maintenance difficulty associated with “minor supports” in boreholes to a certain extent by reinforcing the support strength of “primary supports” in roadway retaining walls. The simulation results are consistent with observed results for the 11 test boreholes, and the accuracy of the numerical simulation is verified.
Highlights
Gas as a resource associated with coal is a type of clean energy but is a dangerous source of energy that threatens safe mining practices in coal mines
How to extract gas safely and efficiently has always been a pertinent issue in coal mine safety in China [1]. e key technology of integrated pillarless coal production and methane extraction is a new gas extraction technology that was developed in recent years on the basis of pressure relief mining technology
According to the occurrence conditions of coal seams, the key layer is first exploited to carry out pressure relief, and the gas extraction roadways arranged in the top/bottom rock stratum of the key layer were replaced by the gob-side retaining roadway [2]. e traditional U-shaped ventilation system was changed to a Y-type ventilation system, in which the pressure-relieved gas that was induced by the mining disturbance was continuously extracted by the drainage boreholes that were drilled behind the face in the gob-side retaining roadway
Summary
Gas as a resource associated with coal is a type of clean energy but is a dangerous source of energy that threatens safe mining practices in coal mines. E above studies used a variety of methods to analyze the stability of the surface ventholes from different angles, but due to significant differences in the layouts of inclined cross-measure boreholes that are drilled in the retaining roadway and surface ventholes, it is necessary to study the space-time evolution characteristics and main influence factors of fracture deformation of the gob-side borehole according to its layout characteristics in order to provide references for the design and protection of underground drainage boreholes. During the mining of panel 1111(1), in order to prevent pressure-relieved gas of overlying coal seam 13-1 from entering into the working face and to eliminate the outburst danger of coal seam 13-1, a group of two inclined crossmeasure boreholes were constructed at intervals of 25 m in the tailgate to extract the overburden pressure-relief gas. The safe and efficient coal and gas simultaneous extraction can be realized
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