Deformation mechanism of a shallow double-arch tunnel in a sloping rock mass

Abstract

The Fuxi double arch tunnel was constructed through a faulted rock mass of metasandstones overlain by slope debris. The paper describes the geological setting, highlighting the poor quality of the ground in the portal area. Following the construction of the exploratory tunnels, the concentrated overburden stress beneath the pillars caused severe deformation and cracking in the tunnel and in the slope above. An integrated analysis was carried out, taking into account the change in stress related to the excavation of the tunnels, the asymmetric pressures and the nature of the fractured overburden. This indicated that control of the tunnel vault deformation was a key step to controlling the deformation of the whole portal area. As a consequence, some additional support was provided to the central pillar prior to the construction of the main tunnels and the secondary lining was installed at an early stage.