Numerical Simulation of New Support Structure for High In-situ Stress Tunnel of Sichuan–Tibet Railway

Abstract

Existing support technology can easily cause the shield machine to jam. A novel ductile support structure is proposed for large deformation tunnels in soft rock along the whole Sichuan–Tibet railway on the basis of the concept of consuming energy of ductile multilevel yielding support. The design of the support structure is to ensure the safety of the shield machine through the large deformation section of soft rock as quickly as possible. In-situ stress data obtained by hydraulic fracturing measurement method were used as boundary conditions of models. The support structure deformation of front shield tunnelling machine and long-term deformation of corrugated steel primary support, steel waist beam and reinforced concrete secondary lining support system were simulated and analysed on FLAC3D software. The variation of the new support structure under the large deformation of soft rock was predicted. Results show that the force path of ductile multilevel yielding support structure is clear. After the excavation of the tunnel and before the application of the concrete lining support, displacement increment of the primary support structure is large. The latter gradually slows down with time, but it still shows an increasing trend. In terms of total displacement distribution, the displacement in the Z direction is obviously larger than that in the X direction, which is consistent with the actual tunnel deformation characteristics. When the tunnel is in operation for 2, 10, 50 and 100 years, stress concentration is found in the arch foot of the assembled supporting system. This condition is mainly manifested as compressive stress after 10 years and tensile stress between 10 and 100 years.