How time-dependency influences the Longitudinal Displacement Profile (LDP) during the construction of deep tunnels

During the excavation of a tunnel the accumulated wall displacement and the loading of tunnel support is the result of both the tunnel advance and the time-dependent behaviour of the surrounding rockmass. The current approach to analyze the wall displacement increase is based on the convergence-confinement method performed with either analytical (closed-form) or the usage of the Longitudinal Displacement Profiles, neglecting the influence of time-dependency resulting in delayed deformation even minutes or hours after excavation. The latter during the preliminary design impacts the time of installation and the type of support system causing safety issues to the working personnel, leading to cost overruns and project delivery delays. This study focuses on investigating and analyzing the total displacements around a circular tunnel in a visco-elastic medium, proposing a new but yet simplified approach that practitioners can use taking into account the effect of time.