Study On Cooperative Control Of Goaf Retaining In Gently Inclined Close Coal Seam Group

In recent years,China’s economy has changed from a stage of high-speed development to a stage of high-quality development,and the growth rate of energy demand has slowed down.Today,China is no longer adapted to the traditional extensive coal mining mode,and is actively promoting the energy revolution.After decades of development,coal resources have gradually moved from "abundant" to "exhausted",and most mining areas have turned to mining in close proximity coal seams.The close coal seam group is a main form of coal occurrence in China,but its mining technology is limited to some extent.Although a large number of scholars have achieved some beneficial results in the mining of gently inclined and close distance coal seams,there is still insufficient research on the collaborative bolting control technology without coal pillars based on this.Based on the basic principles and methods of gob-side entry retaining and collaborative bolting,this thesis comprehensively utilizes research methods such as theoretical analysis,numerical simulation,and field practice to analyze and study the surrounding rock control issues of gob-side entry retaining in gently inclined and shortdistance coal seams,and draws the following conclusions:(1)Theoretical analysis of the mining methods and influencing factors of gently inclined and close distance coal seam groups,the migration law of overlying rock along goaf retaining tunnels,and the deformation and failure law of tunnel surrounding rock.According to the basic roof breaking position of the gob-side entry,a calculation model for the short cantilever beam in the downward mining of the section is established,and the calculation formula for the support resistance of the gently inclined coal seam is deduced.(2)Based on the cooperative anchoring mechanism,numerical simulation and orthogonal analysis were conducted for the influence of multiple factors on anchoring variables,and it was found that the sensitivity of the five influencing factors to the anchoring effect was in the order of spacing>preload>bolt length>anchor length>bolt diameter.The pre tightening force and spacing have the greatest sensitivity to the influence of vertical stress;the anchorage length,bolt length,and bolt diameter have little effect on vertical stress,and the sensitivity of anchorage length and bolt length is similar.Further,the numerical simulation of the anchor bolt anchoring coordination law shows that the vertical stress of the anchor body is positively correlated with the magnitude of the preload at the same spacing.Under the same preload,the vertical stress of the anchor body is negatively correlated with the spacing.According to comprehensive analysis,when the preload is 100 k N and the spacing is 0.8m,the synergy index is the largest,which is the optimal value for anchoring synergy.(3)Research on the collaborative anchoring mechanism of anchor rods,anchor cables,and surrounding rocks through theoretical analysis and numerical simulation.When constructing anchor rods and cables,it is necessary to fully consider the synergy between construction time and deformation,that is,the anchor rod undergoes deformation first,the surrounding rock is depressurized,and then the anchor cable is constructed to achieve the synergy between the anchor rod,anchor cable,and surrounding rock deformation,fully utilizing the best effect brought by its deformation amount.The rationality of this mechanism has been verified through numerical simulation.(4)Based on the theoretical research on the cooperative control of gob-side entry retention in gently inclined and short-distance coal seam groups,a "five high and one low" cooperative anchor technology system for gob-side entry retention is established,including the bolt cable cooperative anchor technology,the bolt(cable)shed cooperative anchor technology,the advanced directional presplitting blasting roof cutting and support technology,and various cooperative anchor technology.The key technologies for controlling some surrounding rocks,on-site problems,and solutions are introduced.(5)Ground penetrating radar(GPR)was used to detect the surrounding rock looseness zone of 11804 transportation roadway.Based on the results and on-site conditions,a support scheme for retaining roadways along the goaf in gently inclined and close range coal seams was designed,and numerical simulation software was used to simulate the retaining roadway scheme,obtaining the stress and deformation laws of the overlying rock in the stope of gently inclined and close range coal seams.The analysis of the stress and deformation of the surrounding rock of the roadway shows that the roof cutting and support scheme designed using collaborative anchor control technology has a good effect on controlling the deformation of the surrounding rock of the goaf retaining roadway.This effectively demonstrates the feasibility of collaborative anchor control technology for the goaf retaining roadway of gently inclined and close distance coal seam groups.(6)The collaborative anchor control technology was applied to the engineering practice of goaf retaining in the gently inclined and close distance coal seam group of Jinhe Coal Mine.During the retaining period,the convergence values of both sides were less than 140 mm,and the convergence values of the roof and floor were less than210 mm.The overall stability control effect of the tunnel was good.The results show that the roadway reservation designed based on collaborative bolting technology in gently inclined and short distance coal seams has small deformation and stable rock pressure,which can meet the requirements of safe production.There are 66 figures,9 tables and 91 references in this thesis.