Study On Overburden Failure Law Of Mining On Thin Bedrock Sandstone Roof Face

During the safe production of coal mines,roof failure of coal mine will cause huge loss to coal mine.Mastering the development law of overburden failure is of great significance for the development of thin bedrock working faces under thick loose layers.Aiming at the overburden failure of Group A coal in ZhangJi Coal Mine of Huainan Mining Group,through the geological analysis,rock mechanical property testing,numerical simulation and electrical detection technique,the overburden failure development characteristics of the research face were obtained.The main conclusions are as follows:The working face is coal mining under thick unconsolidated layers,and the bedrock section of the roof is about 45m.The main lithology is medium-fine sandstone,medium-coarse sandstone and sandy mudstone.The medium-fine sandstone layer has muddy and more muscovite fragments,siliceous calcareous cement,and muddy inclusions.The core rock was tested through the roof rock layer,and the rock mechanical properties were tested,which indicated that the roof sandstone layer in this working face is a hard rock layer.Build models and simulate with FLAC3D software.The results show that during the coal mining process,a plastic failure zone appears in the upper part of the overburden rock,and the roof and floor rock layers of the working face are subject to stress during the coal mining process.Tensile and shear failures occur,with tensile failures in the early stages and shear failures in the later stages.The deformation pattern of the plastic zone of the overlying strata on the working face is in the form of"saddle",and the height of the water conducting fracture zone is 45m.CoMParing with empirical formulas,it is determined that the sandstone roof of this working face belongs to the medium hard roof type.The geoelectric field observation system was deployed on the site to monitor the damage of the roof rock layer during the mining process.The results show that the development height of the caving zone in this working face is 18m,which is located at the interface between medium coarse sandstone and medium fine sandstone;the development height of the diversion fissure zone is more than 40m,close to the bedrock surface.Advance stress effect will arrive 100m earlier.In the monitoring section,the mining height is 4.3m,the ratio of the caving zone to the mining height is 4.19,and the ratio of the diversion fissure zone to the mining height is greater than 9.3.The development of the overburden failure zone of the roof slab in this working face shows that collapse of the overburden is small block,the result reflects that there is no key stratum exist in the roof.Based on numerical simulation results and field measurements,comprehensive analysis determined that the height of the caving zone in the working face was 18m,and the height of the diversion fissure zone was more than 40m,close to the bedrock surface.According to the lithological characteristics and mechanical property tests,the strength types of rock roofs are analyzed,and combined with numerical simulation results and field measurements,it can better analyze and study the dynamic changes in the deformation and deformation of overburden on the working face,reflecting the development law of overburden failure.Figure[20]table[11]reference[108].