Large-scale model tests on face instability of shallow shield tunnels in sand

The failure of tunnel face will occur if the support pressure is insufficient in tunneling. Large-scale model tests on the face stability are conducted for shallow shield tunnels. The collapse of the tunnel face is studied under different velocities of the panel. At the same time, the support pressure and surface deformation are monitored, and the three development stages of the support pressure and surface deformation are discovered. Meanwhile, the digital image correlation is used for the real-time observation and the technology of particle image velocity is further used to deal with the images, thus deriving the incremental displacements of instability soils. It is found that the variation rules of increment displacements are in correspondence with the three development stages of the support pressure and surface deformation.