Study On Optimization Of Key Technologies For Construction Of Extension Of Existing Highway Tunnels

With the rapid economic development,higher and higher requirements are put forward on the traffic capacity of roads,and there are more and more expansion projects of super-large cross-section highway tunnels.Due to terrain constraints and technological development,the extension type of highway tunnels is no longer limited to the type of additional tunnel and the one-sided expansion type.More complex surrounding extension types will also be considered.At present,there is insufficient research on the surrounding expansion form at home and abroad.The selection of the excavation plan for the expansion form around this large-section tunnel,the mechanical characteristics of the surrounding rock and supporting structure during the construction process,the law of stress change of the existing lining structure and the supporting structure need further research.Based on the Loushan Tunnel Expansion Project as the background,this paper compares the excavation methods of the Loushan Highway Tunnel Expansion Project through a combination of theoretical analysis,numerical simulation and monitoring data,and conducts a dynamic construction analysis of the Loushan Tunnel Expansion Process.And based on the actual plan,a new construction plan was proposed,and the stress change law between the existing lining and supporting structure during the construction of the new plan was studied.The main research contents and conclusions are as follows:⑴Based on the analysis of the influence of the tunnel’s sequential route and the surrounding environment,it is proposed that the Loushan Tunnel should be expanded in the form of surrounding expansion.⑵The finite element model was established by MIDAS/GTS,and the surrounding rock displacement and internal force of the supporting structure of three different excavation schemes: first two-side method,first Intermediate method and first upper part method were compared and analyzed,it is believed that first upper part method has a better control effect on the surrounding rock and the force characteristics of the supporting structure are better.Comparing the hyperbolic side wall,the bracket side wall,the trapezoidal side wall and the upright double walls,the bracket side wall is considered to be better in terms of controlling the surrounding rock effect and the force characteristics of the supporting structure.⑶The calculation results of the three-dimensional numerical simulation are verified based on the measured data of the settlement of the vault and the horizontal convergence of the side wall.The results show that the calculated value is basically consistent with the measured value,which verifies the correctness of the numerical simulation.⑷Through numerical simulation,the stress and strain analysis of the surrounding rock and supporting structure during the construction of Loushan Tunnel was carried out,The law of ground settlement,vertical displacement of the vault and inverted arch and horizontal convergence of side wall are obtained.Analyzed the stresses of the supporting structure and the existing lining structure and the mechanical characteristics of the surrounding rock during the construction process.It is believed that the expansion process of the tunnel will have an adverse effect on the existing lining structure near the construction side,but will have an beneficial effect on the existing lining structure far away from the construction side.⑸Based on the comparative analysis of tunnel displacemen between the actual scheme and the new scheme,it is believed that the new plan is better than the actual plan in controlling the deformation of the surrounding rock.Through the analysis of the stress change law between the existing lining and the supporting structure,It is believed that during the entire expansion process,the force of the supporting structure gradually increases,and the force of the existing lining gradually decreases.