Study on deformation characteristics of tunnels excavated in jointed rock masses through field testing and numerical methods

Jointed rock masses contain complexly distributed fractures that have significant impacts on the mechanical behavior of the surrounding rock, especially during the tunneling process. In this paper, a field test was carried out to record the vertical displacement and deformation of the constructing tunnel passing through jointed rock masses. To further investigate the deformation characteristics of tunnels excavated in jointed rock masses, numerical simulations utilizing discrete element methods (DEM) were conducted. Numerical models simulated different sizes and shapes of blocks in jointed rock masses. The results show that during the process of tunnel excavation, the vertical displacement of surrounding rock undergoes the rapid growth phase and the gradual stabilization phase, and the time interval of these two stages is different due to the different depths of the tunnel. In the same monitoring section, the closer to the vault of the tunnel, the larger the vertical displacement of the monitoring point. The displacement value of the section closer to the tunnel face is larger than that far away from the tunnel face, while the tunnel section in shallower buried depth performs relatively larger liner deformation. For the same size of blocks, jointed rock masses formed by tetrahedral blocks perform relatively larger vertical displacement of surrounding rock, deformation of the tunnel, and positive and negative moments of liner structures than those formed by cubic or polyhedral blocks.