Study On Surface Air Leakage Law Of Gob Area In Shallow Buried Coal Seam Under Press-in Ventilation

In the northwest of China,the characteristic of the coalfields are shallow depth,thin bedrock and small coal seams group spacing,the air leakage channels between the working face,the goaf and the ground surface were easily formed when minning,which could cause spontaneous combustion of residual coal.Therefore,it is of great significance to study the law of air leakage in the shallow coal seam gob.This thesis synthetically used theoretical analysis,field experiment and numerical simulation,for the study of the surface gob leakage law at12 Lower 206 stope.Firstly,the formation mechanism of surface cracks and the factors affecting surface air leakage were analyzed.A comprehensive set of measurement methods were adopted to field observation of surface cracks,such as upper and lower coordinate control,determination of ground coordinate,UAV aerial and parameter measurement of surface cracks.Then the range of surface air leakage was measured by double tracer gas method,a series of parameters required for the simulation and the air leakage volume from working face to the gob were obtained.A three-dimensional distribution model of the permeability of the gob which based on the “O” type caving compaction in the gob and the nonlinear seepage theory proposed by Bachmat was established.Using the professional fluid mechanics software-fluent to simulate the flow field in the gob of the 12 Lower 206 stope.Research indicates: In the press-in ventilation mode,the air volume at the working surface leaks to the surface through the gob and the air leakage flow field in the gob is approximately "O"-shaped in the horizontal direction and approximately "bathtub" in the vertical direction since the energy level of the working face is larger than the ground.The three-dimensional permeability distribution model was derived based on the simulation of the airflow field.It is concluded that the permeability is approximately “O” type distribued on the horizontal plane.The closer to the gob boundary,the greater the permeability is.The permeability is first decreased and then increased,and the trend is symmetric.On the vertical plane,the permeability at the same horizontal position gradually decreases as the height increases.The flow field distribution map of the gob at the working face was simulated by means of the modification of the stope model.After the surface cracks sealed,the air leakage velocity in the gob and the air leakage influence range decreased.The influence of different potential energy between the surface and the working face on the air leakage in the gob was analyzed from the perspective of the air potential energy.The result showed that the greater the difference the more air leakage,the relationship,and fitting to get a quadratic function relationship between them.The results of this study have a certain guiding role in the analysis and control of air leakage in shallow coal seam gob.Figure[27] table[19] reference[84].