Abstract: The large deformation is one of tunnel disasters that cannot be completely avoided. When the tunnel is not properly treated after large deformation, it is likely to cause secondary disasters such as arches multiple replacement or tunnel collapses. With the self-designed excavation device and the internal displacement-measuring device for surrounding rock, a physical model test system was used to investigate the tunnel progressive failure, deformation and stress variation during tunnel excavation and buried depth increasing, thus revealing the key supporting parts to prevent large deformation of tunnels. Furthermore, the failure characteristics of the primary lining during large deformation treatment was also studied, and the supporting measures for large deformation treatment were defined. The results are summarised as follows. During the large deformation of the tunnel, the deformation of the vault and the arch bottom are larger than that of the arch waist and arch foot, and the difference increases gradually with the increase of buried depth. The radial and tangential stresses of the vault of tunnel decrease during the large deformation, while the tangential stress of the arch foot increases sharply. When the deformed arch frame is replaced, there may be tension failure at the lining arch near the replacement position, and shear failure at the lining arch waist. Therefore, it is necessary to retain the temporary steel support when the large deformation is observed, and the bottom horizontal support or the temporary inverted arch should be added. This study is helpful to obtain the key prevention and control location during and after the large deformation, which provides guidance and reference for the prevention and safe treatment of large deformation.

Key words: tunnel large deformation, physical model test, excavation device, progressive failure, support key parts