The Channel Expressway: Twin-bored road tunnels under the English Channel

Abstract

Abstract The proposal for a fixed link between France and England by means of a submarine tunnel under the English Channel has been examined in its various aspects of layout, tunnelling, ventilation, safety and operation criteria. The choice of the underground solution has been suggested by the low depth (40–60 m) of the Channel sea bottom between Calais and Dover, and by the presence, at an accesible depth, of a quite continuous geologic stratum of chalk marl with a low permeability and fair compressive strength. The submarine road tunnel is 48 km long and is constituted of two tunnels with an external diameter of 12.10 m. The excavation of the two main tunnels will be done with prototypical tunnel boring machines allotted to the various sections, for an average excavation rate of 25 m per day over a five-year period. The lining is made of precast concrete segments laid by two erectors from the machine itself. The suggested longitudinal ventilation system has short supplementary ventilation tunnels for air filtration, external and adjacent to the main two tunnels and of the same diameter. The ventilation is influenced and facilitated by the input of fresh air from two vertical shafts connected with islands on the open sea. Safety equipment is forseen for communication and information inside the tunnel as well as to guide transit in the dangerous zones. A new lighting system has been proposed.