Abstract
Mining is associated with poor safety due to pressure relief gas emission from the goaf during the production period. The aim of this study was to explore a case study of the Wangjialing coal mine 12322 working face in Shanxi, China, through physical simulation and field observation. The mine is characterized by overlying strata fracture in goaf during the process of working face mining. A mathematical model of gas source emission from the working face and gas migration and the finite element COMSOL software were used to simulate the law of gas migration in the region with overlying strata fissures under the influence of mining. The simulation results were used to explore the law of distribution of pressure relief gas in goaf. Rational parameters of the high-level directional long borehole for the pressure relief gas extraction in goaf were designed based on experimental results. The results showed that the development of the region with overlying strata fissures is affected by mining. In addition, the “trapezoid platform structure” is formed after fracture areas are connected. The maximum height of the stope caving zone was between 26.8 m and 28.1 m, and the maximum height of the fracture zone was approximately 110 m. The gas concentration exhibited a saddle-shaped distribution on the cut surface of the direction of the strike. Furthermore, the gas concentration showed an overall upward trend from the intake airflow roadway to the return airflow roadway and gradually decreased after reaching the maximum. In the vertical direction, gas concentration increased with the increase in the layer, and the position of the highest point of gas concentration gradually shifted to the direction of the intake airflow roadway. Construction parameters of the high directional long borehole were designed through simulation results. After steady extraction and stable extraction, the maximum gas concentration in the upper corner of the working face was 0.49%, and the maximum gas concentration in return airflow was 0.34%. The findings of this study provide information on the law of fracture evolution of overlying strata and gas migration in goaf under the influence of mining. These findings provide a basis for reducing gas overlimit in the working face or return airway corner, thus improving the safety production capacity of the coal mine.
Highlights
Many coal seams in China coal mines are thick continuous coal seams
The problem of high gas accumulation in the return airway corner caused by high gas emission from goaf during coal seam mining has not been fully solved [10, 11]
The buried pipe in goaf and the pressure relief gas Geofluids drainage technology of the high borehole in coal mining are limited by the uncertainty of the gas emission law of the working face and the unclear law of the gas flow field in goaf and the unclear area of the failure of the overlying strata
Summary
Many coal seams in China coal mines are thick continuous coal seams. The coal mines account for about 44% of the total coal reserves in China [1]. The rapid development of mining technology in the coal industry results in an increase in the depth and intensity of mine mining These features result in an increase in mine gas emission quantity. The buried pipe in goaf and the pressure relief gas Geofluids drainage technology of the high borehole in coal mining are limited by the uncertainty of the gas emission law of the working face and the unclear law of the gas flow field in goaf and the unclear area of the failure of the overlying strata. High-efficiency control of gas in goaf is restricted, significantly affecting the safety production of coal mining. The fracture transfixion area of overburden rock under the influence of mining which leads the gas in goaf into the working face under the influence of airflow significantly affects the safety of coal mining. There is a need to explore the distribution characteristics of the overlying strata fracture in the process of working face mining, the law of gas migration in goaf, and gas outbursts from the working face to improve the gas control capacity of mine goaf
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