Research On Optimization Of Step Method Construction Of Large Cross Section Tunnel Of Weak Surrounding Rock

In the construction process of large cross section Tunnels with weak surrounding rocks,CD method,CRD method,double-wall guide pit method,step method and other construction methods are often used.During construction,problems such as narrow construction space and cumbersome procedures are often caused due to more cross-section blocks.Tunnel construction safety and construction efficiency bring many challenges.In order to solve the above problems in the construction method,it is necessary to further study the optimization of the construction method of the large cross section tunnel in weak stratum.The current optimization method is mainly to adjust the number of construction blocks,adjust the temporary support form,adjust the construction sequence,and adjust the parameters of the supporting structure on the basis of the traditional construction method,but fail to fundamentally solve the problems of the traditional method.With the advancement of construction machinery and equipment technology,the Step method + advanced pre-reinforcement construction method is now used instead of the traditional construction method,and research methods such as literature review,theoretical analysis,and numerical calculation are used to increase the step method + advanced pre-reinforcement of the Large cross section tunnel in weak surrounding rock.The pre-reinforced construction method is studied,and the main research contents are:(1)Research on the failure mode of the large cross section tunnel construction in weak surrounding rock;(2)Research on the stability of the weak surrounding rock stability in the large cross section tunnel construction;(3)Weak cross section rock large cross section tunnel adopts the Step method + advanced pipe shed construction with different combined design parameters,Pipe shed reinforcement length and pipe shed reinforcement angle to study the stability of weak Surrounding rock;(4)The step method + advanced pipe shed is weak Surrounding rock large cross section tunnel application,analysis of surrounding rock and supporting structure stability and construction efficiency.Analyze the numerical calculation results and find that the step method has two failure modes: premature failure and post-failure in the construction of a large cross section tunnel with weak surrounding rock.According to the premature failure mode,the prereinforcement measures of the advanced pipe shed are proposed,and Suggestions are made for the design method of the bench method,the length of the pipe shed reinforcement and the angle of the pipe shed reinforcement for the large section tunnel in weak surrounding rock using the step method + advanced pipe roof construction.The construction monitoring data shows that the construction method can meet the requirements of construction safety control.This construction method is more conducive to controlling the deformation of the surrounding rock than the traditional construction method;although the construction increases the construction process of the advanced pipe shed,increases the investment of time and materials,However,the application of the advanced pipe shed is beneficial to the stability of the surrounding rock.At the same time,the application of the pipe shed increases the value of the design parameters of the step method construction,which is conducive to the use of large machinery and speeds up the construction progress.