Research On Movement Law Of Overlying Rock And Mine Pressure Control Technology In Lower Thin Coal Seam Mining Of Shallow Coal Seam Group

The coal seam in the northern Shaanxi mining area is shallowly buried,and there are coal seam groups composed of multi-layer coals.Some coal mines have entered the lower coal seam mining in the coal seam group.stage.This thesis takes Liangshuijing Coal Mine in the northern Shaanxi mining area as the research object.Through the combination of laboratory test,numerical simulation and theoretical analysis,the research on the overlying rock activity law and the mining pressure control technology of the lower thin coal seam of the shallow coal seam group is carried out.The main research conclusions are as follows:（1）Research on the o structure of the lower coal seam and the stress environment before mining.According to the key layer theory,the rock structure of the coal seam group in Liangshuijing Coal Mine was determined,and the stress,deformation and failure characteristics of the overlying rock before the mining of the4^-3 coal were analyzed,and the stress release effect of the upper coal on the interval rock layer was revealed.The influence of rock formation damage,determine the significant disturbance range（20m）and deformation disturbance range（10m）of upper coal mining on interval rock formations.（2）Overburden rock activity and mining pressure in lower coal seams.The influence of coal mining on the structural state of key layers under different ratio between mining and spacing.（1）When the coal seam group is mined with a low ratio between mining and spacing:The top interface of the fracture zone of the lower coal exceeds the height of the key layer,and the key layer of the lower coal is in a state of"passive equilibrium structure"that is easily unstable after the fracture,resulting in the activation and instability of the key layer of the upper coal.Repeated compaction areas appear from bottom to top,and large and small periods of high dynamic load and low static load will be formed in the lower coal stope to show the phenomenon of compaction;（2）When the coal seam group is mined with an intermediate ratio between mining and spacing:The top interface of the lower coal fissure zone is located in the key layer,the lower coal key layer is in a state of"balanced structure"that can maintain its own stability after the fracture,and the upper coal overlying rock is activated but not unstable.After the activation of the upper coal key layer,it affects the appearance of the mine pressure in the lower coal stope in the form of static load.（3）When the coal seam group is mined with high ratio between mining and spacing:The top interface of the lower coal fracture zone is located below the sub-key layer.After the lower coal is mined,the lower coal key layer is in a state of"bending and sinking",which not only affects the mining pressure of the lower coal stope but also controls the overburden.Rock movement,the mineral pressure appearance is similar to that of single coal seam mining,and the pressure step is stable.（4）When the lower coal seam is mined under different mining ratios,the different activation states of the upper coal key seam lead to different characteristics of the lower coal stope.The influence of dynamic load of coal stope increases,which increases the difficulty of roof control.（3）Mining pressure control technology for lower coal seam mining.（1）Mechanical analysis of broken structure:Based on the masonry beam three-hinge arch structure,establish the mechanical model and mechanical criterion of broken hinged structure activation instability,analyze the controllable mining factors affecting the activation and instability of the structure,（2）Roof control technology:According to the results of mechanical analysis,the technical means of controlling the activation and instability of the lower coal mining roof by using the support strength and the mining speed are proposed.It is determined that when the pushing speed of the lower coal working face is greater than 7.2m/d,the dynamic load of the stope increases significantly;when the support resistance of the support is 9000k N,and the initial support force is 6300k N（70%）,the stope roof can be controlled safely and efficiently,and the stope roof can be controlled safely and efficiently.In the industrial test,a good mine pressure control effect was obtained.The thesis has 53 figures,14 tables,and 83 references.