Influence of overburden separation grout filling on the evolution characteristics of spontaneous combustion hazard zones in the goaf

Abstract

During coal mining, the application of overburden separation grout filling (OSGF), i.e., grout injection into the separation layer within the overburden through surface boreholes, serves to control the deformation and fracturing of key strata in the overburden and significantly reduce surface subsidence. However, its resultant disturbance to the stress field will change the compaction characteristics of the goaf and thus affect the spontaneous combustion hazard zones there. In view of this fact, with a Y-shaped ventilation working face of Tunlan Coal Mine as the research prototype, the evolutions of the flow field and spontaneous combustion hazard zones in the goaf under OSGF disturbance were comprehensively investigated through coal seam excavation experiments, flow field similarity experiments, on-site coal mine measurements, and CFD simulation of goaf. The following research findings were obtained. First, OSGF avoids the air leakage from the working face to the deep part of the goaf to a certain extent, thereby weakening the oxidation capacity of the compacted area and its rear area. Secondly, as the working face advances, the relative distance between the working face and the adjacent grouting boreholes changes periodically, leading to dynamic changes in the spontaneous combustion risk zone in the goaf, with the oxidation zone fluctuating within a range of 38.4 m. Among OSGF-related borehole parameters, the borehole spacing affects the spontaneous combustion zones the most, followed by the number of borehole rows and the borehole influence radius in sequence. This study reveals the impact and mechanism of OSGF on the flow field and spontaneous combustion hazard zones in the goaf, which provides a theoretical basis for the safe application of OSGF and the prevention and control of spontaneous combustion disasters in goafs.