Study On The Mechanism Of Harmful Gas Discharge In Goaf Of Double System Coal Seam Mining In Datong Mining Area

There are Jurassic and Carboniferous coal seams in Datong mining area.The No.3-5 coal seam in the main mining of Carboniferous belongs to the extra-thick coal seam.Due to the large thickness of the mining coal seam and the wide range of mining influence,the mining-induced cracks in the stope may be connected with the upper Jurassic goaf,resulting in the potential safety hazard of the harmful gas released from the upper Jurassic goaf to the Carboniferous stope,thereby causing the harmful gas overrun in the Carboniferous working face.This disaster-causing phenomenon has occurred repeatedly in the Carboniferous working face with the mining characteristics of the bi-system coal seam in Datong mining area.Therefore,in this paper,the mechanism of harmful gas discharge in goaf of extra thick coal seam mining is studied.Based on the key stratum theory and material mechanics theory,the failure development process and development height of rock are analyzed.Combined with the FLAC^3D numerical simulation method,the connectivity characteristics of double goaf in the mining process of 8207working face were determined.Based on the analysis of harmful gas discharge conditions,the quantitative criteria for disaster characteristics of different types of connected channels are established.Four equivalent parameters are selected as control factors,and the multi-parameter control equation of harmful gas emission in Jurassic goaf is constructed.The rationality of the control equation is verified by field measurement and analysis.The COMSOL multi-field coupling simulation software was used to analyze the disaster-causing mechanism of the dual-system goaf,and the monitoring data of the mine gas monitoring system were used to verify the effectiveness of the high-level drainage roadway harmful gas interception system for the prevention and control of harmful gases.The results show that the rock failure height of 8207 working face is 170.9 m,which belongs to the type III connectivity characteristic:the flow field between the two goafs is connected and can cause disasters;It is calculated that the harmful gas of 9403-10112m³ is released from the Jurassic goaf to the 8207 working face and its goaf within 2h when the main key rock layer of 8207 working face is broken,causing the volume of harmful gas in the stope to increase by 30-33%within 2h.It is preliminarily determined that when the pressure difference between the flow fields is greater than 200 Pa and the air conduction crack channel between the two systems is greater than 0.14 m,the discharge can occur.When the pressure difference between the flow fields is greater than 400 Pa and the air conduction crack channel between the two systems is greater than 0.4 m,it may cause disaster.It is verified that the interception system of high pumping roadway can effectively intercept and discharge the harmful gases discharged from the upper goaf.By studying the connection characteristics between 8207 working face and upper goaf,the quantitative relationship of harmful gas discharge was established,and the discharge conditions and disaster law of harmful gas in upper goaf were revealed.The application and promotion of research results can provide support for the development of harmful gas prevention technology in similar multi-seam mining faces.The paper has 40 figures,10 tables,and 62 references.