Pressure Relief Gas Drainage in a Fully Mechanised Mining Face Based on the Comprehensive Determination of ‘Three Zones’ Development Height

Abstract

The gas emission from the goaf generates gas in the upper corner of the working face, and the return airflow exceeds safe limits. The identification of the reasonable level of the high-long borehole is the key factor to ensure the effectiveness of its extraction. On-site test at the 2308 working face of Licun Coal Industry of Lu’an Chemical Industry Group, the development of coal overlying strata fracture was studied through derivation of theoretical and empirical formulae, physical similarity experiment, and UDEC numerical simulation: this was then combined with in-situ microseismic monitoring to obtain the distribution characteristics of mining overburden “falling zone” and “overbreak zone” under the actual working conditions, and accurately design the high-level long borehole end hole layer. The results show that the height of the falling zone is 17.5 m to 20.5 m, and the overbreak zone is 43.5 m to 49.5 m. When the hole position is between 25 m and 30 m in the middle and lower part of the overbreak zone, the flow and concentration of gas extracted by drilling are high, and the pure amount of gas extracted by a single hole is increased by 53% (on average). The investigation of pressure relief gas extraction shows that throughout the mining period, the average gas concentration in the return airway is maintained below 0.36%, and the average gas concentration in the upper corner is kept within 0.48% (effective gas control). The research proves the rationality of the arrangement of the high-level long borehole horizon in the working face and provides a reference for the design of the borehole horizon in the future gas drainage and control in the goaf.