| Coal seams are usually occurred in sedimentary rocks with obviously bedded structures and lower strength.Roadway excavations in coal mine are mostly driving along the coal seams.And many of the roadways has a layered surrounding rock with high bedding plane frequency,low strength and often containing weak intercalated layers.After excavation,these roadways have a poor stability,a large deformation,and a long stabilization period.With the gradual depletion of coal resources shallow in depth and easy to exploitation in China,the worse geological conditions and the more complicated stress environment has caused support failure,high repair frequency,and maintenance difficulties of roadway with layered surrounding rock(RLSR).Meanwhile,increaseing the length and number of the anchor support components and repeated repairing during the support design and repair period did not effectively control the deformation and failure of RLSR,but reduced the excavation speed of roadway and aggravated the pressed situation of mining arrangement.Therefore,it is urgent to propose a more scientific support strategy and effective support technology for the roadway support with layered surrounding rock and complicated stress enviromment.The support structure combined anchor cable and c-shaped tube(ACC)is a new tape of support components which can fully exert the axial stress state improving action and the shear resistance action in controlling stability of RLSR,and can greatly improve the shear strength and stability of the layered surrounding rock.This paper take the stability control of a RLSR under high horizontal stress as engineering background,a combination of theoretical analysis,mechanical experiments,numerical simulation,similar simulation,engineering monitoring and other research methods is used to explore the mechanical characteristics of ACC and its advantages in roadway support.By analyzing the influencing factors of RLSR deformation and failure characteristics,the instability mechanism of RLSR has been revealed,and then the targeted support strategies of ACC are proposed for the stability control of RLSR.The stability of RLSR influenced by high horizontal stress under the support of ACC has been studied,and the support effect monitoring in actual engineering were carried out.The main conclusions are drawing as follows:(1)Mechanical properties of ACC and its interaction with surrounding rock.ACC can provide a lateral shear resistance to the surrounding rock under the premise of ensuring high pre-tightening force and axial working load of the internal anchor cable,and the c-shaped tube can protect the internal anchor cable from shear failure due to the uneven tension and shear force.The range of shear failure and required shear resistance for stable support of the layered surrounding rock was estimated theoretically,and the reasonable geometric parameters of ACC has been deduced.The distribution law of prestress field generated by the pressure applied by anchor cable to the surrounding rock and c-shaped tube to the borehole was studied,and the concept of energy dissipation of ACC has been proposed.(2)Shear properties analysis of structural plane supported by ACC,Direct shear test of the structural plane under different support conditions designed by similar model simulation theory was carried out.Find that,the shear strength parameters and the maximum shear displacement of the structural plane support by ACC were better than those of the traditional anchor cable support,and the shear resistance response of structural plane supported by ACC is more sensitive which can provide a stability and durable shear resistance to the structure plane.The shear mechanical model of the structural plane under ACC support was established,and the calculating method for equivalent shear strength parameters of structural plane supported by ACC was proposed.(3)Influence factors analysis of the deformation and failure mechanism of RLSR.Numerical simulation results showed that the higher frequence of the bedding plane in the surrounding rock,the more significant influence of the shear strength index of bedding plane on the deformation and failure of RLSR.The floor stability was more sensitive to the variation of bedding plane frequency,the strength of rock layer and the horizontal stress,while the roof was more sensitive to the variation of the shear strength of bedding plane.The sidewalls were most affected by the variation of the friction angle of bedding plane between coal seam and rock mass.With the increase of horizontal stress coefficient and the angles between roadway strike and the maximum horizontal principal stress,the plastic zone was almost constant in the sidewalls,but the amount of movement of the coal in sidewalls continues to increase.It is proved that under high horizontal stress,there would be more overall slip deformation in the sidewalls of RLSR.(4)Deformation and failure mechanism of RLSR and its support stratrgy.The deformation and failure characteristics of RLSR under horizontal stress in Nanguan coal mine were analyzed.The mechanism of instability and large deformation were discussed.It is showen that the deformation and failure of RLSR was mainly performing as the overall internal deformation of the sidewalls along the bedding plane between coal seam and its roof and floor,and the bed separation faliure of roof and floor,this process has been aggravated by the high horizontal stress.Improving the shear strength,enhancing the support of sidewalls to the roof and floor,and reducing the generalization span of the layered rock mass in the roof and floor is the key to controlling the stability of RLSR.The cooperative support scheme combined ACC and rock bolt and the whole section support scheme of ACC were proposed which are more suitable for RLSR.(5)Similar model simulation experiment of RLSR stability with improvedACC support scheme.The stress distribution and deformation law and its failure mechnism of RLSR under different support stratrgy were studied by similar model simulation.RLSR without support has been failed when loaded to the stress of 250 m depth.RLSR with traditional support had a larger deformation and was unable to meet the normal use when loading to the stress of 500 m depth.While RLSR with cooperative support scheme combined ACC and rock bolt has a section shrinkage of 30%compared with RLSR with traditional support when loaded to the stress of 500 m depth.And the roadway could be used normally after re-excavating floor.Furthermore,RLSR with whole section support scheme of ACC has a section shrinkage of only 12%and the floor heaves is reduced by 81%compared with RLSR with traditional support when loaded to the stress of 500 m depth,the layered surrounding rock in the floor was effectively controlled at the same time.(6)Numerical simulation experiment of RLSR stability with improved ACC support scheme.Numerical simulation has showen that the optimized ACC support stratrgy is more effective in controlling the shear stress concentration and shear displacement of the bedding plane in surrounding rock mass,since they could reduce the displacement of the bedding plane,and improve the bearing capacity of the layered surrounding rock and sidewalls,reduce the deformation and damage degree,and then improve the stability of RLSR.The whole section support scheme of ACC could control the deformation of the floor,enhance the integrity of the roadway surrounding rock mass and was the most effective support scheme of RLSR.(7)Engineering application of ACC support scheme.The production process and construction technology of ACC were introduced.The engineering application and monitoring of RLSR supported by ACC scheme were carried out in the mining roadways of No.3214 working face in Nanguan coal mine.It showed that ACC had a good support effect and applicability in RLSR under high horizontal stress. |
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