Stability Analysis Of Surrounding Rock And Supporting Structure Of Unsymmetrical Pressure And Shallow Tunnel In Earth-rock Interface Stratum

When constructing a tunnel in the earth-rock interface stratum,due to the uneven strength of surrounding rock,if reasonable support measures or proper construction methods are not adopted,deformation of surrounding rock and supporting structure may be exacerbated,and uneven supporting force appear in the supporting structure.Cracking and even tunnel collapse may occur,so it is of great significance to carry out research on the deformation and stress characteristics of the tunnel during the construction of unsymmetrical pressure and shallow tunnel in earth-rock interface stratum.Relying on the Damagou tunnel project of Jiu Mian expressway in Sichuan province,this paper uses indoor model tests and numerical simulation methods to carry out the deformation and stress characteristics of the surrounding rock and supporting structure before and after the pre-reinforcement of the tunnel under the condition of unsymmetrical pressure and shallow tunnel in earth-rock interface stratum,and the influence of different excavation methods on surrounding rock is analyzed.The main research work of this paper is as follows:（1）According to the actual engineering situation on the site,based on the similarity principle to determine the model test similarity ratio,select reasonable similar materials,independently design and produce model test box,and design displacement,stress and structural internal force monitoring schemes to carry out model tests.（2）Aiming at the two conditions of pre-reinforcement without retaining wall and pre-reinforcement with retaining wall,the variation law of the ground surface settlement,vault settlement,surrounding rock stress and the internal force of the supporting structure under the condition of unsymmetrical pressure are studied through indoor model tests.The result reveals its distribution and development laws.（3）Using FLAC^3Dnumerical simulation software,a three-dimensional tunnel model is established,which simulates five types of tunnels without pre-reinforcement,using pipe shed,using retaining wall,using pipe shed and retaining wall,using pipe shed,retaining wall and surface grouting.Under the working conditions,the deformation of the surrounding rock,the stress of the supporting structure and the distribution rules of the plastic area are analyzed.At the same time,the model test results are compared with the numerical simulation results to verify the reliability of the numerical simulation results.（4）Using FLAC^3Dnumerical simulation software,to simulate the effects of excavation of the ring cutting method,CD method and CRD method on the surrounding rock after pre-reinforcement of the tunnel using pipe shed,retaining wall and surface grouting.According to the simulation results and in view of safety,construction progress and project cost,a better excavation method is proposed.The research results of this paper can not only provide references for on-site construction,but also provide some theoretical basis and technical reference for the design and construction of similar projects in the future.