Study On Excavation Method Of Large Span Underground Cavern By Pulling Apart Anchor

With the development of underground engineering technology,the underground cavern has gradually developed in the direction of large span,large section and deep buried.In the current construction practice of large-span underground caverns,in order to ensure the safety and stability of the caverns after excavation,the partial excavation method is mostly used.However,with the development of underground engineering,partial excavation method can not meet the development requirements of construction mechanization in some scenarios,so it is necessary to carry out the optimization research of construction method which can meet the requirements of large section excavation.In recent years,the bolt support structure which is rising in the coal roadway and developed in the highway tunnel can improve the bearing capacity of the whole surrounding rock bearing circle.Therefore,the excavation of the underground cavern with the bolt combined support as the initial support can expand the single excavation section or change the excavation method on the premise of ensuring safety,so as to greatly speed up the construction speed.Therefore,this paper carries out the research on the excavation method of large-span underground cavern by anchor pulling(1)In the aspect of theoretical analysis,the paper studies the concept of removing the core soil which plays the role of "internal support" in the double side wall heading method and CRD method,which is commonly used in large span excavation,and replacing the stress by long anchor bolt which can anchor into deep and stable surrounding rock to act as "external pulling";and the stress change of surrounding rock caused by the transformation of working method is introduced by the theory of distributed excavation The feasibility of this concept is pointed out by analyzing.(2)Based on the concept of large-span anchor excavation method,the influence of bolt length and steel arch frame model on the tunnel construction by anchor excavation method is studied.The results show that long "external pulling" bolt can anchor into stable surrounding rock,and control the deformation of tunnel better.I22 b steel arch can bear the internal force and bending moment caused by surrounding rock deformation,and make the internal force and the internal force and the bending moment of the surrounding rock deformation better The bending moment distribution is more uniform.The method of anchor excavation with this design parameter is used to control the deformation and stress of surrounding rock slightly better than that of the traditional two side wall heading method.(3)Through model test,the failure mode of long-span anchor excavation method is studied.With the increase of overburden load,the pressure is first transmitted to the arch top,which causes cracks on the tunnel vault;the cracks appear in the tunnel arch and invert arch.At this time,the original stress balance of the supporting structure is broken,and the bending moment at the arch foot of the tunnel is larger,which leads to the external tension and internal tension of the position The stress state of side pressure leads to the arch foot crack;after that,the surrounding rock at the bottom of the invert is squeezed by the deep surrounding rock,which leads to the shear dislocation between the surrounding rock at the bottom of the invert and the surrounding rock on both sides of the side wall,and finally the tunnel is damaged.The results show that the distribution trend of soil pressure is similar,and the correctness of the above analysis is verified.(4)The method of anchor excavation suitable for grade IV surrounding rock in Chongqing is applied to practical engineering.By the method of monitoring data feedback analysis,the displacement of surrounding rock,the axial force of anchor bolt and the stress of steel arch frame are compared with the numerical simulation and model test.The change trend and difference are analyzed.The results show that the numerical simulation results are consistent with the trend of monitoring feedback,indicating that the large span is consistent with the trend of monitoring feedback Applicability of the method of degree anchor excavation in grade IV surrounding rock in Chongqing.