Gibraltar Tunnel Project update - the geomechanical challenges / Gibraltar Tunnel Projektaktualisierung - die geomechanischen Herausforderungen

The Gibraltar strait connection project is a very complex one, from its history to the various aspects of the present design stage. The preliminary design of the Gibraltar Tunnel was ready in 1996 but its revision became unavoidable because of the new findings about the geological conditions. The design update turned out to be rather more than a simple design review. The geotechnical characteristics had to be reconsidered for the purpose of the geomechanical computations, which focused on the possibility to realise the tunnel in the worst possible conditions: 200 meters of ground overburden and 50 atmospheres of water pressure is a quite different situation from the one the tunnelling industry is usually facing. Through a broad series of analyses (2D and 3D) and parametric studies, it was possible to ascertain that from a geotechnical point of view the tunnel is feasible provided a series of conditions are fulfilled. The feasibility depends on the possible working conditions for slurry shields or EPB. The drainage is an important factor in order to modify the stress field around the tunnel. Apart from in depth knowledge of the hydrogeological and geotechnical characteristics of the breccias in the centre of the Strait, major technological developments over the next years will be necessary for allowing the construction of the Gibraltar Tunnel.