How was the Eurotunnel built across the English Channel?
It took 7 years, 4,000 workers and a secret weapon, geology, to complete the most daring engineering challenge of the 20th century.The Eurotunnel, or Channel Tunnel, is 50.45 km long and connects Folkestone, England, to Coquelles, France - near Calais, in just 35 minutes of crossing. It is an incredible feat of engineering characterized by the longest underwater tunnel in the world with an underwater section that extends for 39 km under the bed of the English Channel.
The entire infrastructure is made up of two railway tunnels with a diameter of 7.6 m and a service tunnel, in case of emergencies, with a diameter of 4.8 m. It took 7 years, 4,000 workers and a secret weapon to build it: geology. Through the geological study of the subsoil it was possible to establish the trajectory of the excavation and the route that the Eurotunnel would follow.
The construction technique of the Channel Tunnel
But how was the Channel Tunnel built? The great challenge to face was to understand at what depth to position the tunnel and which geological level to drill. One of the key techniques was the so-called “seismic reflection”, a kind of X-ray of the ground that allows to visualize the geological layers and whether they are wavy, deformed or crossed by faults. To carry out the drilling, drills called Tunnel Boring Machines (TBM) were used: these “mechanical moles” are 200 m long, have a diameter of 7.6 m and a rotating disk with steel blades, and are capable of excavating 36 thousand tons of rock per day.
The TBM is controlled by a computerized system that, together with a laser, calculates the trajectory. As the cutter advances, the TBM then creates a ring of reinforced concrete lining for the tunnel, made up of 5 curved segments called segments, which serve to resist the intense pressure from above.
On December 1, 1990, the French and English teams met halfway, with a difference in height of only 35 cm thanks to constant measurements. The two completed tunnels are equipped with 245 passages to reach the emergency tunnel, fire doors and a highly efficient cooling and ventilation system. The only way to cross the tunnel is by train, such as the high-speed train that takes you from Paris to London in just two hours, or the shuttle service for vehicles called “le Shuttle”.
This train is very special because it takes on board the entire vehicle you are traveling with until the transit is completed, taking you from Calais to Folkestone in just 35 minutes.
