Study On Evaluation Method Of Surrounding Rock Reinforcement Body Stability Of Roadway Under Bolt Support

The stability of the surrounding rock under the anchor support depends on the stability of the surrounding rock within the reinforcement range of the anchor.At present,the understanding of the physical and mechanical properties and stability of surrounding rock within the scope of anchor reinforcement is not sufficient.Therefore,a comprehensive and accurate understanding of the anchor reinforcement mechanism and quantitative evaluation of the surrounding rock stability of the anchored roadway can provide an important theoretical basis and practical significance for roadway excavation and support.This paper relies on the N1212 return air duct in Ningtiaota Coal Mine as the project,based on the elastic-plastic theory,unified strength theory and surrounding rock strength strengthening theory,the changes of physical and mechanical parameters of surrounding rock,the stability of surrounding rock in anchorage area after anchor reinforcement and support effect are analyzed.The main conclusions are as follows:(1)The traditional support theory relies on the plastic zone of the surrounding rock or the width of the fracture zone to carry out the bolt support design,and the width of the plastic zone and the fracture zone are often difficult to determine in practical engineering.However,a large number of research show that the stability of the roadway actually depends on the stability of the anchored surrounding rock.This paper adopts the idea of homogenization,and the anchor-surrounded rock composite bearing structure is equivalent to the uniform and continuous isotropic surrounding rock reinforcement body,which is used to indicate the physical and mechanical properties and deformation state of the surrounding rock in the anchorage reinforcement area.Based on the elastic theory and the established displacement equivalent conditions,the expression of the physical and mechanical parameters of the surrounding rock reinforcement body is derived.(2)The surrounding rock reinforcement body is regarded as a new supporting structure,and the mechanical model of coordinated deformation of surrounding rock reinforcement body and deep surrounding rock is established.The analytical solution of stress and displacement of surrounding rock reinforcement body and deep surrounding rock and the plastic radius expression of surrounding rock reinforcement body are obtained.Based on the deformation and damage degree of surrounding rock reinforcement body,the stability coefficient of surrounding rock is defined,which indicates the proportion of surrounding rock reinforcement body stability zone in surrounding rock reinforcement body,and a new method for evaluating the stability of surrounding rock of roadway is proposed.(3)The theoretical values are compared with the numerical simulation results,and the influence parameters of the surrounding rock stability coefficients are analyzed.The results show that the theoretical calculations agree well with the numerical simulation results,which verifies the reliability of the methods and results.The pretightening force of the bolt and the stability coefficient of the surrounding rock show a linear change.The dilatancy angle of rock mass has no effect on the stability coefficient of surrounding rock,but it has a great influence on the displacement of the surrounding rock reinforcement body damage zone.The intermediate principal stress has a great influence on the stability coefficient of surrounding rock and the displacement of surrounding rock.(4)Combined with the engineering example,the surrounding rock stability coefficient k under the corresponding working conditions is combined with the measured displacement value to evaluate the anchoring effect of the surrounding rock of the roadway,and the reinforcement effect of the bolt is effectively evaluated,and the work efficiency and economic benefit are improved.If 0<k<1,the arrangement of the spacing between the anchors satisfies the support requirements,the anchoring effect is better,and the surrounding rock of the roadway is stable;On the contrary,the surrounding rock of the roadway is unstable,and it is necessary to reduce the spacing between the anchors or increase the length of the bolt to improve the strength of the bolt support.