Performance of a Long Pipe Roof for a Large Span Shallow Tunnel below an Existing Highway

The pipe roof reinforcement is usually used to stabilize the tunnel arch for tunneling in weak ground section or passing below highway. In this study, large scale pipe-roof (85m long and ϕ 159 mm) was used to enhance the Shitougang Tunnel where a railway tunnel passes below the Hengyang-Kunming Highway in China. The deformation of the pipe was measured by a series of strain gauges, and meanwhile, a three dimensional numerical analysis was carried out to investigate the mechanical performance of the long and larger pipe roof. The measured results are in good agreement with the numerical results. They both show that the stress distribution of the pipe roof can be divided into three sections: tension section ahead of tunnel face, compressive section behind the tunnel face and tension section near the entrance casing arch. The peak stress value occurs close to the entrance casing arch and a certain distance ahead and behind the tunnel face, respectively. This analysis illustrates the mechanical response of large and long pipe roof reinforcement used for a shallow tunnel passing below highway.