Support design method for deep soft-rock tunnels in non-hydrostatic high in-situ stress field

Due to the long-term plate tectonic movements in southwestern China, the in-situ stress field in deep formations is complex. When passing through deep soft-rock mass under non-hydrostatic high in-situ stress field, tunnels will suffer serious asymmetric deformation. There is no available support design method for tunnels under such a situation in existing studies to clarify the support time and support stiffness. This study first analyzed the mechanical behavior of tunnels in non-hydrostatic in-situ stress field and derived the theoretical equations of the ground squeezing curve (GSC) and ground loosening curve (GLC). Then, based on the convergence confinement theory, the support design method of deep soft-rock tunnels under non-hydrostatic high in-situ stress field was established considering both squeezing and loosening pressures. In addition, this method can provide the clear support time and support stiffness of the second layer of initial support. The proposed design method was applied to the Wanhe tunnel of the China-Laos railway in China. Monitoring data indicated that the optimal support scheme had a good effect on controlling the tunnel deformation in non-hydrostatic high in-situ stress field. Field applications showed that the secondary lining could be constructed properly.