The Gibraltar Tunnel will link the two continents: Europe and Africa. The 40 km tunnel presets the alternative to the proposed bridge. The only suitable position is along a submarine ridge between the two continents at a maximum depth of
300 m, where the strait is 29 km wide, not at the strait narrowest point. After its initial version (1996), the project had to be updated, adopting a substantially different alignment and longitudinal profile.
The realized perforations along the sea bottom present a huge risk if encountered during the excavation. The poor characteristics of the weak breccia associated with the upper highly permeable biogenetic limestone deposit requires a deeper route in order to ensure the safety against water ingress during construction.
The approach to safety aspects led to adopting similar project setup to that of the recently developed projects for the Alpine crossing.
The rail technological aspects require a specific approach because high gradients (max. 3%) are required in order to reach the great depth without an excessive tunnel length.
Many other aspects, such as the possible relevant movement of the European towards the African continent remain to be examined in the next design phase.
The project is foreseen to be realized by EPB or slurry shield TBM. Execution and final layout options considering the presence/absence of the service/escape tunnel were studied, with immediate or graduated completion.