Study on Air Leakage Law and Coal Spontaneous Combustion Danger Area in Goaf of Ultra-Long Fully Mechanized Mining Faces with Large Mining Height.

Abstract

The mined-out areas of high-seam, ultra-long fully mechanized coal mining faces exhibit a high degree of fracture development and complex airflow fields. Additionally, the slow advancement speed of the working face can easily lead to oxidation and spontaneous combustion of residual coal in the mined-out areas, posing a threat to mine safety production. In this paper, the influence of different mining heights and different working face lengths on the failure of overlying strata in goaf is analyzed by means of numerical simulation and field observation. The influence of the working face length on the air leakage law in the goaf is studied, and the dangerous area of coal spontaneous combustion is divided. The results indicate that as the mining height increases, the delamination rate in the caving and delamination zones of the mined-out areas gradually increases, leading to an increase in porosity and permeability. With the increase in face length, the plastic deformation range of goaf expands, the porosity and permeability of the compacted zones gradually decrease, and the separation area continues to increase. The primary air leakage sources in the mined-out areas of high-seam, ultra-long fully mechanized mining faces are located in the intake corner and at a distance of 160-220 m from the working face along the dip direction. The main air leakage sinks are located in the return corner and at a distance of 20-80 m from the working face along the dip direction. When the working face length increases from 100 to 400 m, the pressure difference between the intake and return airways at both ends increases, and the fracture development in the "delamination zone" of the mined-out areas becomes more pronounced. This results in an expanded air leakage range and causes the hazardous areas of spontaneous combustion to move 51 m deeper into the mined-out areas, and the range increases by 61 m along the trend. Combined with the actual situation of the mining area, comprehensive prevention and control methods such as cyclic nitrogen injection inerting, air leakage plugging, and strengthening monitoring system are proposed, which provides strong support for mine fire prevention and extinguishing work.