Numerical simulation of ground air leakage into the gob based on surface cracks observation: a case study in Shendong coalfield of China

Air leakage into mining gob is one of the main causes of spontaneous combustion of coal. This study investigated the 22310 working face of Bulianta mine to establish a 3D permeability model in the gob of shallow coal seam. Meanwhile, distribution law of ground air leakage into gob was studied. First, the surface cracks of 22310 working face were observed. The compaction area in gob was analyzed based on observation results of surface cracks. Secondly, 3D permeability distribution model of 22310 gob was established according to a range of compaction area and distribution of vertical three-zone above gob through using “O”-style caving compaction theory. Finally, numerical simulation of air leakage flow field in gob of 22310 working face was performed through adopting FLUENT software, combining the nonlinear seepage in gob. Results show that the ground cracks distribution is similar to the “O”-style distribution of gob. The width of cracks is small in the middle of gob. The cracks are more obvious when the distance is closer to gob boundary. The caving compaction zone of 22310 gob is the area where strike distance being greater than 110 m from working face and the inclination distance being greater than 33 m from boundary of two roadways. Meanwhile, surface air leakage flows into the return airway through gob because of air gravity. Flow field in gob also presents an approximate “O”-style distribution in the horizontal direction and a “bathtub”-type distribution in the vertical direction. This research has certain guiding benefits to the numerical analysis and control of air leakage in compound gobs of shallow coal seams.