With the development of the tunneling construction method, modern Tunnel Boring Machine (TBM) can excavate in almost all rock conditions. It can achieve simultaneous and continuous operations of tunnel construction, such as excavation, support and slag-out, as well as guide and monitor all operations. TBM is automated large-scale tunnel construction equipment, which integrates technologies of mechanical engineering, electric and electronic engineering, information engineering, as well as telemetry and tele-control system engineering.
The area of plastic zones gradually increases along the tunnel route, but it becomes stable after the rear shield. The vault has a larger plastic zone than the invert, attributing to the geometrical difference between the cutter-head and the front shield, as well as the conicity of the front and rear shields. The invert experiences three unloading processes, due to excavation, the contact between the rear shield and the bottom of surrounding rock, as well as backfill grouting at gap between the lining and the rock mass. The simulation results indicate that the stress paths at the vault are relatively simple, and the stress concentration caused by excavation unloading is obviously reduced by lining and backfill grouting, while the sidewall is less disturbed by the excavation of TBM. The characteristics of stress field and plastic zone on the cross and longitudinal section of the tunnel were analyzed in detail, and the results were compared with those in the intrinsic condition (when TBM model is not activated). The failure modes of surrounding rock mass described based on the cohesion weakening and frictional strengthening (CWFS) Mohr-Coulomb strain-softening criterion. In order to study the mechanical response of a hard rock tunnel excavated by double shield tunnel boring machine (DS-TBM), a numerical method was introduced to simulate the TBM excavating process.
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