Study On Excavation And Support Technology For Large Section Tunnel Of Badaling Underground Station In Beijing-Zhangjiakou Intercity Railway

Since the completion of the first high-speed railway(Beijing-Tianjin inter-city railway),high-speed railway has developed rapidly in China.When passing through tunnels,considering the aerodynamics problem,the tunnel section is usually larger,In general,the excavation of large cross-section tunnel will cause great disturbance to the surrounding rock mass.How to ensure the stability of the surrounding rock and the safety of the lining structure are the important engineering problems that need to be overcome.This paper studies the key technical problems in the large span excavation of the station through a variety of research methods,based on the first deep underground railway station(the Beijing-Zhangzhou inter-city railway station,which is built in the mountains).The construction scheme is studied from the angle of surrounding rock deformation,surrounding rock stress and plastic zone,lining stress,and the optimal scheme is selected.Using the topology optimization function of ABAQUS,the optimal structure of large span steel is calculated by using strain energy as the objective function.Through the study of the influence of different length,prestressing and stiffness anchorage cable on the deformation of surrounding rock,the principle of determining the supporting parameters of anchor cable in early branch is obtained.Achieve the following main results:(1)On the basis of the design scheme,two new schemes,such as pillar method and three-step seven-step method,are proposed,and three kinds of excavation schemes are studied and the optimal scheme is selected.Three steps of seven steps in the control of the stability of the surrounding rock and ensure the safety of the two aspects are inadequate,this program can be ruled out.Although the final dome settlement is larger than that of the reserved rock pillar method,the vault subsidence of this scheme is developing slowly at all stages of excavation.When the pillar is retained in the upper rock pillar,Large,so in the control of the stability of the surrounding rock,the design scheme is better than the reserved rock column method.In order to ensure the structural safety,the advantage of the pillar method is obvious.The maximum tensile stress of the initial lining is obviously smaller than that of the design.It can ensure that the lining will not be damaged by the lining,so long as it can ensure that the upper pillar is supported.Will produce the smallest perturbation of the surrounding rock.In summary,the reserved pillar method is the best scheme.(2)Using ABAQUS topology optimization function to optimize the one-quarter ring steel,the calculated results are in accordance with the law of "two large and medium small",and on this basis,the large-span steel structure of Badaling underground station is optimized According to the analysis of the optimized structure,the steel cross section size selection scheme of "strengthening arch foot arch,weakening arch top arch" is obtained,and compared with the results of stress monitoring of initial section of loess section,the selection scheme is verified rationality.(3)The influence of the length,stiffness and prestress of the large span anchor on the deformation of the surrounding rock shows that the length of the anchor cable plays a key role in controlling the deformation of the surrounding rock.In the case of anchors,the axial force of the bolt is obviously reduced,and the increase of the length of the anchor cable also makes the axial force distribution of the anchor at different positions more balanced,so as to effectively control the deformation of the surrounding rock under the premise of avoiding their own tensile damage The Although the increase of prestressing force and stiffness of anchor cable can control the deformation of surrounding rock better,but the effect is not significant.The design of these two supporting parameters is mainly considered to meet the tensile strength of anchor cable Requirements,in the tensile strength is guaranteed under the premise of the anchor cable can be as much as possible to increase the prestress or reduce its diameter.