Construction stability analysis of large section highway tunnel portal section based on numerical analysis

Abstract

Abstract the entrance portal of No.8 tunnel of F3 bid section of E60 highway in Georgia is shallow buried and under unsymmetrical pressure, which leads to high risk and difficulty in tunnel construction. Tunnel 8 is designed based on ADECO-RS (analysis of controlled deformation in rock and soil). In order to understand the stability characteristics of tunnel portal in the whole section construction process and determine reasonable and feasible engineering countermeasures, the numerical simulation analysis of tunnel construction process is carried out. We not only studied the relationship between the stability of the slope at the entrance and the stability of the whole tunnel body under the actual stratum conditions, but also studied the mechanical and deformation characteristics of the surrounding rock and supporting structure of the tunnel.The numerical analysis results show that the stability characteristics of the portal slope directly affect the overall stability of the tunnel portal section; due to the disturbance of tunnel excavation, a large range of plastic zone appears at the interface of rock and soil at the portal section, resulting in large settlement deformation of vault. The collapse and deformation of the upper soil layer with poor engineering properties will cause excessive additional load on the supporting structure of the tunnel.Therefore, advance support measures should be taken to control the excessive deformation of vault. At the same time, due to the influence of asymmetric pressure, the supporting structure of the shallow buried side and the deep buried side of the tunnel appears obvious asymmetric pressure state. It is suggested to strengthen the stiffness of the shallow buried side support structure and adopt the asymmetric support structure to ensure the safety of the support structure.