Deformation Control Technology of Soft Surrounding Rock in Shallow Buried Section of Surrounding Expanded Tunnel

Based on the in-situ extension project of a tunnel, the dynamic construction process of the surrounding extended-excavation was simulated through finite element method. The displacement and deformation, the stress distribution of the tunnel’s weak surrounding rock, and the mechanics and of the supporting structure are obtained. The calculation results are compared with the field monitoring data, and the two results are basically consistent. The following conclusions are obtained: (1) The use of step-by-step excavation and timely temporary support has a significant effect on controlling the deformation of weak surrounding rock. (2) The demolition of the existing lining has a great disturbance to the surrounding rock of the tunnel. There will be a certain range of plastic deformation at the side arch foot, and the design parameters of the pipe shed at the arch spandrels and the lock foot anchor rod at the arch foot should be strengthened to ensure the construction quality and improve the stability of the surrounding rock. (3) The spandrels and arch foot on the left and right sides of the primary support, and the connection between the initial support and the vertical temporary support are relatively weak positions. During the construction of the arch spandrels and the arch foot, more attention should be paid to the deformation and displacement of the surrounding rock and the support structure. It is hoped that the research results can provide reference for the design and construction of similar projects.