\label{fig:Profile80} Profile of the ground level altitude on top of the 80-km tunnel, taken from Ref.~\cite{cite:Osborne}. The possible shaft locations are numbered from 1 to 8. In red is shown a 30-km by-pass tunnel, needed to avoid digging the very deep shafts 4 and 5. It is possible that this problem may disappear with the 100-km version of the tunnel, for which a feasibility assessment is ongoing. 