Stability Of Coal Wall And Interaction Mechanism With Support In Fully Mechanized Working Face With Great Mining Height

In the fully mechanized working face with great mining height(FGH), the stability of coal wall is significantly affected by the joint and fracture of the coal seam, the stability of the support is also affected. Furthermore the inter-action of support and surrounding rock in the FGH can be influenced. In order to solve these problems, a combination of field research, theoretical analysis, similar simulation, numerical simulation, industrial test and other research methods is carrier out to deeply and systematically analyse the instability characteristics of coal wall affected by the damage of joint and fracture, the interaction mechanism of coal wall and support as well as the corresponding control technology. The research results have important theoretical value and practical significance to ensure the safe and efficiency mining in the FGH.By studying the effect of joint damage to the coal wall and the mining stress distribution in the FGH, the results shows that along with the increase of joint inclination the damage to the coal wall presents the trend of increase-decrease-increase, the damage to the coal wall presents the trend of firstly decreases then increases along with the azimuth angle increasing and the damage will decrease along with the increase of joint spacing. According to the influence analysis of mining height to coal wall support ability, the concept of weakening coefficient was proposed to characterize the weakening effect of mining height to coal wall support ability in hard and medium hard coal seam. The abutment pressure in the limit equilibrium zone is inversely proportional with the mining height and the damage extent of coal wall and proportional with the mechanical parameters(E、C) of soft coal seam.Based on the effect of joint damage to the coal wall and the distribution of mining stress in the FGH, the extended evolution of the joint and fracture, the temporal and spatial variation law of the distribution feature of the deformation destabilization area and coal wall displacements of the FGH are analyzed in this dissertation. The size, density and the propagation and coalescence of joint and fracture in coal seam are found to be influenced by primary joint occurrence. The deformation and failure feature of coal wall is the macro performance of the extended evolution of the joint and fracture. Under the condition of hard or medium hard coal seam, the stability of coal wall is mainly influenced by working face pressure when the joint inclination angle is 90°. The easily rib-spalling area on working face is close to the intersecting lines and the relative position of these area is mainly influenced by the joint inclination angle and azimuth when there are intersecting lines existing between joint and working face. The shorter the distance between joint is, the smaller the crushing unit of coal wall will be, the wider the easily rib-spalling area will be, and the lower the stability of coal wall will be. Under the condition of soft coal seam, the easy rib-palling area of working face is located in the middle of the coal wall, the smaller the physical and mechanical parameters of coal mass are, the easier the destabilization of coal wall will be.The designed and developed the simulation support and hydraulic control system can be used to research the interaction between the supports and surrounding rocks in FGH. This research obtained results of the law of support setting load influenced on destabilization of coal wall in FGH, the law of destabilization of coal wall and roof activity influenced on the position and state and loading feature of support by experiments. This dissertation also obtained results including the “P0—ΔB” functions of support setting load and the stability of coal wall like some kind of hyperbolic by experiments. Under the condition of FGH, the degree of interaction among rib-palling of coal wall, end-face fall and the bad position and state of support are more obvious.The mechanical model of the interaction between support, roof and coal wall in the FGH was built to reveal the interaction mechanism of the three based on the “given deformation” and the “given load”, the way how the main roof impact to the support and coal wall. The supporting strength in the FGH and the subsidence of direct roof are approximately linearly increasing with the depth of coal wall rib-spalling and the rotating angle of the main roof increasing. There is a similar hyperbolic relationship between the subsidence of direct roof and the depth of coal wall rib-spalling with the supporting strength of the support in the FGH. Because of the rotating angle of the main roof increasing, the coal wall rib-spalling become deeper and the maximum depth tends to the distance between the fracture line of the main roof and the coal wall in the FGH.The control methods of the coal wall and support stability were developed based on the interaction mechanism and carried out successfully in the industrial experimental test. Significant technical results have been achieved. In the extremely-soft coal seam, the stability of coal wall was effectively improved by using the advanced deep hole static pressure water injection technology. The frequency, the average depth and length of coal wall rib-spalling was reduced respectively by 80%, 35% and 50%. In order to ensure the support stability in the FGH with hard roof, the advanced loosen blasting technology was used and the degree and frequency of coal wall rib-spalling reduced significantly.