Study On Fracture Characteristics Of Overlying Strata And Stability Of Surrounding Rock In Narrow Coal Pillar Gob-side Entry Driving

Strong mining has an obvious adverse effect on the stability of roadway surrounding rock,and the cooperative relationship between different coal pillar widths and caving strata on mining site and the stress transfer law are the fundamental basis for the control of roadway surrounding rock under strong dynamic pressure and narrow coal pillar conditions.Based on the idea of coupling effect of stress transfer under the influence of caving and mining of gob-side entry driving with narrow coal pillar,this thesis closely focuses on two key scientific issues,namely,the size of section coal pillar and the support of roadway surrounding rock under bias pressure,through the research methods of mine pressure theory,finite difference method,numerical simulation and similar simulation test,the comprehensive research on the macro and meso levels is carried out to determine the influence law of the size change of section coal pillar on the breaking and stress distribution of the overlying strata of roadway surrounding rock during roadway driving,the relationship between the change of the width of the narrow coal pillar and the stress environment of the stope is established,and the stability of the roadway under the condition of dynamic pressure is revealed,the non-uniform roadway surrounding rock support method is further realized,which provides a theoretical basis for the future layout of mining face and roadway surrounding rock support design.The main conclusions are as follows:（1）Through the key stratum theory and UDEC numerical simulation,the causes of instability of roadway surrounding rock in the process of basic roof breaking are studied,the interaction mechanism between the movement of overlying rock structure and the stability of roadway surrounding rock is revealed,and the influence of different width of narrow coal pillar and different section shape of roadway on the fracture of roadway surrounding rock is discussed.According to the simulation analysis of the fracture characteristics of the overlying rock,the fracture form of the basic roof has a significant influence on the stability of the narrow coal pillar and the surrounding rock of the roadway.The farther the fracture position is from the roadway,the smaller the influence on the stability of the surrounding rock of the roadway.After the fracture structure is formed,the influence of the basic roof on the surrounding rock of the roadway becomes smaller and smaller with the increase of the width of the coal pillar.（2）Through the similar simulation test bench and FLAC^3D numerical simulation software,the physical model and numerical model of narrow coal pillar are constructed respectively.The influence of narrow coal pillar size on the stress of roadway surrounding rock under dynamic and static changes is simulated,and the stress transfer mechanism between narrow coal pillar and roadway solid coal is revealed.The similar simulation test shows that the 6m coal pillar bears well in the process of roadway excavation.In the process of coal pillar shrinking from 30m to 3m,the vertical stress growth rate in the narrow coal pillar is larger than that of the solid coal side,which proves that the coal pillar is the main bearing structure in the excavation process.The numerical simulation test shows that with the increase of the size of the coal pillar,the stress concentration formed by the stress transfer of the goaf in the coal pillar is getting larger and larger,and the stress concentration gradually approaches the center of the coal pillar from the side near the goaf,while the stress peak on the solid coal side shows a decreasing trend,and the decreasing rate shows a first increase and then decrease.（3）By analyzing the stress distribution characteristics of roadway surrounding rock under different height conditions and without roof cutting,the variation trend of stress distribution and displacement of roadway surrounding rock after roof cutting is obtained,and the transfer law of stress in narrow coal pillar between roof cutting and solid coal side of roadway is revealed.It is found that the stress distribution and displacement show the opposite trend under the condition of roof cutting and non-roof cutting.The roof cutting not only reduces the peak stress but also avoids the occurrence of natural disasters caused by air leakage to the goaf.（4）Aiming at the problem of asymmetric failure of roadway surrounding rock in narrow coal pillar protection,based on the original uniform strength support scheme,the asymmetric support method is adopted to reinforce the roadway surrounding rock according to the support emphasis.When the narrow coal pillar side adds an anchor cable on the basis of the original support scheme,the overall compressive stress value of the compressive stress zone is increased,which effectively makes up for the defect of the limited length of the anchor rod and increases the range of the active support stress field.The improved asymmetric support scheme can effectively realize the asymmetric control of coal pillar and roadway roof,and ensure the overall stability of roadway use.