Numerical modelling of existing tunnels subjected to time dependent threats

Dealing with time-dependent phenomena during tunnel excavation and management is a complex topic that engineers and geologists need to face worldwide. Threats to tunnel stability are posed by the swelling/creep behaviour of geomaterials. These phenomena occur during the construction of the tunnel but can evolve for a long period after tunnel operation and can jeopardize the tunnel integrity with time. Although the topic of time-dependent behaviour has been repeatedly addressed in the literature, less attention has been paid to methodologies to deal with it during the serviceability of tunnels. Therefore, appropriate and reliable methods are needed to analyse and predict tunnel behaviour during their service life and/or refurbishment processes. This paper will focus on existing tunnels subjected to the time-dependent behaviour of the surrounding ground to identify the methodological approach for designing maintenance works and/or managing the associated risks. Examples from the Authors' experience are used to support the discussion.