Tuesday’s marvels of engineering: Channel Tunnel
Channel Tunnel Source: BBC

Channel Tunnel, also called Eurotunnel, rail tunnel between England and France that runs beneath the English Channel.

The Channel Tunnel, 31 miles (50 km) long, consists of three tunnels: two for rail traffic and a central tunnel for services and security. The tunnel runs between Folkestone, England, and Sangatte (near Calais), France, and is used for both freight and passenger traffic.

Passengers can travel either by ordinary rail coach or within their own motor vehicles, which are loaded onto special railcars. Trains can travel through the tunnel at speeds as high as 100 miles (160 km) per hour; the trip takes about 35 minutes.

The Channel Tunnel, completed in 1994 and officially opened on May 6 of that year, is considered one of the most amazing engineering feats of the 20th century.

Overview of the Channel Tunnel

For centuries, crossing the English Channel via boat or ferry had been considered a miserable task. The often inclement weather and choppy water could make even the most seasoned traveler seasick. It is perhaps not surprising then that as early as 1802 plans were being made for an alternate route across the English Channel.

Channel tunnel
Source: Pixabay

The Design for the Channel Tunnels

The Channel Tunnel was to be made up of two parallel railway tunnels that would be dug under the English Channel. Between these two railway tunnels would run a third, smaller tunnel that would be used for maintenance, as well as providing a space for drainage pipes, etc.

Each of the trains that would run through the Channel would be able to hold cars and trucks. This would enable personal vehicles to go through the Channel Tunnel without having individual drivers face such a long, underground drive.

The plan was expected to cost $3.6 billion.

Getting Started

Just getting started on the Channel Tunnel was a monumental task. Funds had to be raised (over 50 large banks gave loans), experienced engineers had to be found, 13,000 skilled and unskilled workers had to be hired and housed, and special tunnel boring machines had to be designed and built.

As these things were getting done, the designers had to determine exactly where the tunnel was to be dug. Specifically, the geology of the bottom of the English Channel had to be carefully examined. It was determined that although the bottom was made of a thick layer of chalk, the Lower Chalk layer, made up of chalk marl, would be the easiest to bore through.

Building the Channel Tunnel

The digging of the Channel Tunnel began simultaneously from the British and the French coasts, with the finished tunnel meeting in the middle. On the British side, the digging began near Shakespeare Cliff outside of Dover; the French side began near the village of Sangatte.

Channel Tunnel
Source: Wiki

The digging was done by huge tunnel boring machines, known as TBMs, which cut through the chalk, collected the debris, and transported the debris behind it using conveyor belts. Then this debris, known as spoil, would be hauled up to the surface via railroad wagons (British side) or mixed with water and pumped out through a pipeline (French side).

As the TBMs bore through the chalk, the sides of the newly dug tunnel had to be lined with concrete. This concrete lining was to help the tunnel withstand the intense pressure from above as well as to help waterproof the tunnel.

Connecting the Tunnels

One of the most difficult tasks on the Channel Tunnel project was making sure that both the British side of the tunnel and the French side actually met up in the middle. Special lasers and surveying equipment was used; however, with such a large project, no one was sure it would actually work.

Since the service tunnel was the first to be dug, it was the joining of the two sides of this tunnel that caused the most fanfare. On December 1, 1990, the meeting of the two sides was officially celebrated. Two workers, one British (Graham Fagg) and one French (Philippe Cozette), were chosen by lottery to be the first to shake hands through the opening. After them, hundreds of workers crossed to the other side in celebration of this amazing achievement. For the first time in history, Great Britain and France were connected.

First meeting
First meeting
Source: Ice.org

Finishing the Channel Tunnel

Although the meeting of the two sides of the service tunnel was a cause of great celebration, it certainly wasn’t the end of the Channel Tunnel building project.

Both the British and the French kept digging. The two sides met in the northern running tunnel on May 22, 1991, and then, only a month later, the two sides met in the middle of the southern running tunnel on June 28, 1991.

That too wasn’t the end of the Channel construction. Crossover tunnels, land tunnels from the coast to the terminals, piston relief ducts, electrical systems, fireproof doors, the ventilation system, and train tracks all had to be added. Also, large train terminals had to be built at Folkestone in Great Britain and Coquelles in France.

The Channel Tunnel Opens

On December 10, 1993, the first test run was completed through the entire Channel Tunnel. After additional fine-tuning, the Channel Tunnel officially opened on May 6, 1994.

After six years of construction and $15 billion spent (some sources say upwards of $21 billion), the Channel Tunnel was finally complete.