Study On The Evolution Law Of Roof Fissures In Deep 11-2 Coal Mining Of Panxie Mining Area

The gradual depletion of shallow coal resources makes the problem of deep mining increasingly obvious.Sandstone fissure water,commonly found in coal measures,is an important factor affecting the normal production of mines.The fracture development and distribution of water abundance are also inseparable.The changes in the fracture of the roof of the coal seam during the mining process will affect the water filling conditions of the fractured sandstone water to the working face.Therefore,the study of the development and evolution of the crack in the roof of the coal seam under the deep mining conditions has a guiding role for the prevention and treatment of the water damage of the coal system sandstone.Based on the basic geological data collected in the Panxie mining area,the paper analyzes the thickness of the coal seam,the coal burial depth,the combined characteristics of the lithology of the overlying strata,the rock thickness statistics,and the characteristics of the rock present stress in the 11-2 coal in the mining area.Seven indicators from the geostress field characteristics,overburden rock mechanical properties and mine ground temperature distribution were selected.According to the differences between these indicators in the deep and shallow parts,the deep boundary of the mining area was determined by MATLAB cluster analysis.The 730 m burial depth combined with the depth of the 11-2 coal in the mining area results in a deep partial coverage of the Panshee and Guqiao mines.The second mining area in the south of Guqiao Coal Mine was selected as the specific engineering background to analyze the roof hydrogeological and engineering geological conditions of 11-2 coal.A deep mining geological conceptual model and UDEC numerical model were established to simulate cracks during coal mining.The morphological and stress state change process was studied to study the deep roof rock fracture development rules of the 11-2 coal.The results of the research are as follows:(1)The roof occurred first collapse at the time of mining 40 m which height was about 7.90 m,and then periodically occurred at a step distance of 21 m.(2)As the advancing distance increases,according to the changes in the fractal dimension of mining fissures,the lateral closing range of roof cracks,and the maximum development height of stress-reducing areas,the development of the fracture could be divided into three stages which are rapid development of fissures(stress drastic change period),slow development of fissures(stress dynamic equilibrium period)and stable development of fissures(stress variation stability period).Correspondingly,the step distance is 20 m to 60 m,60m to 120 m,and 120 m to 180 m.(3)The closure of cracks and the stress recovery phenomenon in the roof during mining process reveals the overburden rock has a certain self-healing ability.Grasping the development law of deep coal mining roof fissures.and combining with hydrogeological conditions,such as water abundance and water pressure in aquifers,can be predicted during mining water inrush prone areas and prone stage.