Research On Surrounding Rock Control Technology Of Roadway In Room And Pillar Goaf With Hard Roof

The reasonable application of roadway support technology is of great significance to give full play to the role of the support structure and to ensure the stability of the roadway surrounding rock.In this paper,taking Zhuangzihe No.15 coal hard-roof room-and-pillar goaf as the research object,by means of on-site investigation,drilling and peeping,laboratory mechanical experiments,theoretical analysis,numerical simulation analysis and field industrial tests,the research of the roadway passing through the hard roof is carried out.The layout and support scheme of the room-and-pillar goaf reveals the stress distribution characteristics of the surrounding rock when the roadway is excavated in the goaf,and clarifies the main points of support for the room-and-pillar goaf in the roadway with a hard roof.Through on-site industrial tests,the roadway support scheme proposed in this paper has achieved good results in engineering applications.The main conclusions of the paper are as follows:(1)On-site investigation,downhole drilling peep and laboratory mechanical parameter test were carried out on the surrounding rock of the goaf.The on-site investigation results show that the roof of the goaf is basically complete,and the bottom plate is all bulged,and the bulging amount varies from 0.3 m to the top.The peeping results of multiple roof peepholes comprehensively show that the roof has broken zones with thicknesses of 400 mm and 300 mm at 1.5 to 1.9 m and 5.2 to 5.5 m,respectively,and broken and longitudinal cracks at 6.5 to7 m.There are separation layers at 3.5 m and 4.4 m,and separation layers and longitudinal fissures at 4.7-5.2 m.The measurement results of the laboratory mechanical parameters of the surrounding rock in the goaf show that the average compressive strength of the roof limestone is 172.35 MPa,the average tensile strength is 3.21 MPa,and the average elastic modulus is54.47 GPa.The compressive strength is 32.93 MPa,the average tensile strength is 1.79 MPa,and the average elastic modulus is 6.69 GPa,which belongs to the unstable bottom plate..(2)Based on the theoretical calculation of the key layer,the roof load of the goaf is351.75 k Pa,and according to the thin plate theory,the initial pressure step distance of the roof of the goaf is 50.65-81.70 m.Theoretical calculation shows that the average load of the coal pillar under the limit empty area is 6.85 MPa,the ultimate strength is 18.82 MPa,the stability safety factor is 2.75,and the coal pillar has good stability.Through numerical simulation analysis of the gob instability law,the results show that when the side length of the positive deformation room-pillar goaf is 5-30 m,the roof is sheared and damaged,the depth increases from 1.5 m to 3.2 m,and the side length of the gob is increased from 1.5 m to 3.2 m.When reaching 40 m,the rock mass at the depth of 7 m of the roof began to be damaged by shearing,and tensile stress appeared on the local surface of the roof.When the side length reaches 50 m,the tensile stress failure area of the roof increases suddenly,extending to the deep rock mass,and the roof may be unstable,which is similar to the theoretical calculation of the initial caving step distance of the roof.The stability of the bearing area of different coal pillars is analyzed by numerical simulation in the limit empty area.The results show that when the side length of the positive deformation coal pillar is reduced to 5 m,the vertical stress in the center of the coal pillar is 16.8 MPa,and the proportion of the elastic zone is 25.5%,the stability is poor.When the side length of the normal deformation coal pillar is reduced to 4 m,the vertical stress in the center of the coal pillar is 24.2 MPa,all of which are plastically damaged,and the coal pillar loses its bearing capacity.The numerical simulation results of the stress distribution and plastic failure form of the surrounding rock in the goaf show that the maximum suspension subsidence of the roof is 6.70 mm,the maximum vertical stress is 5.12 MPa,which is less than twice the original rock stress,and the roof suspension is basically not damaged by tensile stress.,the top plate has good stability,the bottom plate bulges,the vertical stress is smaller than the original rock stress,the minimum is 0.043 MPa,the rock rheological phenomenon occurs,and the bottom plate is seriously weakened.The numerical simulation results of the coal pillar when the roadway passes through the limit span show that due to the redistribution of the surrounding rock stress in the goaf,the surrounding rock of the goaf is in a stable state,and when the roadway passes through the coal pillar,the stress on the roof of the goaf and the remaining coal pillar is affected.The distribution,type of plastic failure and the size of the area have little effect,and the roof of the goaf and the surrounding rock of the roadway have better stability.(3)Based on the good stability of the roof of the goaf and the weakened lithology of the floor bulge,combined with the separation of the roof,the distribution of the broken zone and the deformation characteristics of the surrounding rock of the roadway,the support of the return air roadway through the hard roof and the room-and-pillar goaf is proposed.care technology: Three anchor cables and six anchor rods are arranged in each row of the roof.The dimensions of the anchor cables and anchor rods are φ17.8×7500 mm and φ20×2200 mm respectively,and the row spacings are 1700×2000 mm and 1000×1000 mm respectively.The support scheme in which the 12-gauge I-beam strap cap wears the boots and the cap boots are fixed with two anchor rods,respectively,is φ22×1200 mm and φ22×1800 mm.It has been verified by industrial tests that the deformation of the surrounding rock of the roadway is stable for about 20 to 25 days,and the maximum approach of the roadway and roof and floor is 40.9 mm and 32.1 mm,respectively,which effectively controls the surrounding rock of the roadway passing through the hard roof and room-and-pillar goaf.It can meet the requirements of mine production and provide a reference for the control of surrounding rock of roadway under similar production geological conditions.