Evolution Of The Mining Pressure Mechanism Surrounding Gob-side Entry And Control Method Of Close Coal Seams In Haishiwan Mine

During the Haishiwan deep coal seam mining process,the mining of the upper and lower coal seam faces will induce different effects on the mine rock pressure in the coal seam and adjacent coal seams.At present,the characteristics of these influences and the mechanism behind them are uncertain.Particularly,the evolution of overburden structure caused by close coal seam mining and its influence on the stress distribution of surrounding rock required theoretical perfection.Based on the close-range coal seam mining engineering under deep conditions,similar materials simulation experiments,in-situ pressure and deformation monitoring,theoretical model analysis,and three-dimensional numerical simulation is used to cover the surrounding rock layers in different mining processes.The evolution and movement characteristics are expounded.The form and mechanism of the surrounding rock stress affected by the change are simulated and analyzed,and the mining pressure and deformation law of the deep coal seam roadway in different coal seam working faces are revealed.According to the characteristics of the failure and deformation of the key stratum and its controlled rock strata,the source and distribution characteristics of the mine pressure increment before and after the sub-fault and the main key stratum are proposed.Different from the single coal seam mining conditions,the stress and failure modes of the basic roof between the double-coal mining activities in close proximity and its important influence on the overlying strata structure are pointed out.Aiming at the stress distribution characteristics and stability hazard of surrounding rock in close distance coal seam roadway,the pressure relief technology of roadway surrounding rock with blasting top pressure relief as the main method was proposed.The relevant parameters were designed and the unloading effect was simulated.The main research results of the thesis are as follows:(1)The structural patterns and evolution characteristics of overburden strata under different mining stages in the near-distance coal seam mining process are analyzed.By observing similar material simulation experiments,according to whether the main key layer in the overburden is unstable or broken,the pressure state of the roadway is divided into two periods.Before the main key layer was broken,the near-field structure was the main source of mine pressure increment,and the mine pressure had small fluctuations.After the main key layer was broken,the far-field.structure played a major role in the increase of mine pressure in close coal seams.And make its changes have a typical jump.(2)Summarize the stress characteristics of the coal seam face in the near-distance coal seam mining and its interaction with the overburden structure.The recovery of the lower coal seam is often after part or all of the upper coal seams are recovered.At this time,the main key layer is often broken and a certain stable structure is formed.The failure mode of mining under the coal seam under this structure is analyzed.It is proposed that the "falling with mining" method will accumulate the block stability structure of the key layer of overlying strata and lead to block instability and pressure’ s jumping changes.(3)An evolution model of overburden structure is established based on multiple layers of key layers.Based on the theory of elastic deformation and the theory of "masonry beam",the increment of mine abutment pressure under different coal seams and different working face mining conditions and its influence on the pressure of the lower working face and roadway are solved.For the goaf formed after the upper coal seam is mined,a key block model is established to solve the stress distribution of the lower coal seam roof.(4)It points that the breaking of the main key layer and its block motion are the most prominent factors affecting the mine pressure in close coal seam mining.Aiming at the stress and deformation characteristics of the roadway in multiple working faces in the upper and lower coal seams,through the field measurement,theoretical analysis,simulation verification and other means,the distribution law of mine pressure in each roadway is summarized,and the cause of the mine pressure in relation to the overburden spatial structure at that time is analyzed.The major stress or instability factors of the roadway under different working conditions are manifested.(5)The study found the dynamic amplification effect of the roadway boundary under impact ground pressure.In the range of loose circles around the roadway,the degree of dynamic response is inversely related to its distance from the boundary.,that is,the degree of dynamic response gradually increases from the boundary of the loose ring to the boundary of the roadway and reaches the maximum at the surface of the roadway.In the design of the roadway and its surrounding support,the difference in dynamic response at different locations should be considered.(6)The stress distribution mode and countermeasures of the surrounding rock when the roadway is affected by the near-distance coal seam mining and its own excavation are proposed.According to the structural characteristics and movement forms of the overlying rock layer(block),the pressure relief scheme and the support parameter adjustment method were determined.By analyzing various fields such as displacement,stress,and damage around the roadway in simulation experiments,the effects of pressure relief and support adjustment are verified.