In the Alps, building the world's longest tunnel (photos)

SEDRUN, Switzerland--Deep under the Swiss Alps, workers are putting the finishing touches on the world's longest tunnel. This is the Gotthard Tunnel, and at 57 kilometers long and 800 meters below the surface, it is intended to drastically slash the amount of truck traffic carrying cargo over the Alps.

The project is nearly 20 years in the making and is expected to be completed in 2017. And because it is not just one tunnel, but two that are each one-way, the entire system required more than 151 kilometers of tunnel excavation, counting crossover tunnels, emergency stations, and other sections.

Seen here is the fork where trains can continue to head in the direction they were going, or switch to the crossover tunnel. That is expected to be done in cases of maintenance on one of the two one-way tunnels, or when there is an accident.

Most of the major excavation work was done using a tunnel-boring machine like this one.

In order to work on the ceiling of the tunnel, workers had to set up major scaffolding, like seen here.

Underneath its smooth concrete surface, the tunnel has three layers: a drainage layer, a waterproofing layer, and an inner shell. Seen here, a section of the tunnel has different layers showing and in progress.

A worker adds part of the protective membrane to the ceiling inside the Sedrun section of the Gotthard Tunnel, the world's longest tunnel.

Here we see a section of the tunnel fully covered in the protective membrane. It will then be covered in concrete and smoothed out.

Anyone heading deep into the tunnel--800 meters below the surface--must first descent from the town of Sedrun on this little cable car.

In this small office in Sedrun, a worker can monitor the control room monitors and see what is going on in several different places at once. Here, with computers, one person can run the ventilation system, the electrical system, traffic inside the 800-foot-deep shaft, and keep track of who's inside the tunnel.

A look at a computer screen, on which the controller can monitor what's going on deep inside the tunnel.

At Staziun Alpina, small trains (that were once used in the construction of the Eurotunnel, otherwise known as the Chunnel) ferry workers from the surface to the shaft elevator that takes them 800 meters below the surface.

The driver of the train offers a passenger a cigarette.

Through the window of the small train, it is possible to see the entrance to the Sedrun portal to the Gotthard Tunnel.

Through the window of the train, it is possible to see deep into the 1 kilometer long tunnel that leads to the 800-meter-high shaft that takes workers and visitors down into the main tunnel system.

At the bottom of the shaft there is a giant chamber, where workers come to and fro, and several small trains are gathered to take people or materials around.

After years of work, this is a nearly finished section of the Gotthard Tunnel. Note the smooth interior surface. Under that concrete are several layers designed to keep the tunnel solid and to keep it dry.

One important element of the tunnel project is the construction of two emergency stations designed to quickly and safely offload passengers from a burning train. Though the stations are 20 kilometers apart, the idea is that if a troubled train can make it to the station, passengers can quickly disembark and escape through special tubes that take them to adjacent safety tunnels. Those tunnels, because of a slight overpressure, are supposed to be free of smoke, no matter how much is coming from a burning train.

A fire door is designed to keep fire and smoke out of the passageways through which passengers on troubled trains can escape.

There are seven ventilation shafts like this one above the emergency stations. The idea is that smoke can be lifted out quickly, making it easy for passengers to escape a burning train that has made it to the emergency station without smoke inhalation.

If a train cannot make it to the emergency station, there are still escape passageways every 325 meters throughout the tunnel, though they only lead passengers to the parallel one-way tunnel rather than to a fully safe and secure section of tunnel.

This is a finished connecting passageway. There are sections like this every 325 meters throughout the tunnel. These passageways can allow anyone to escape a troubled train that cannot make it to an emergency station.

Gotthard Tunnel planners decided to future-proof the project by excavating a cavern where a major train station could be built in the future. This station, which could be the deepest underground in the world, as well as the highest elevation major station in the world, could serve as many as 3,000 skiers a day in Sedrun, Switzerland. But there are no plans to finish this part of the project. Instead, the cavern will be closed off from the main tunnel. The idea, though, is that by digging out the cavern now, it opens the possibility of the station in the future, while not doing it now would prohibit its ever being done.

In a major tunnel system, ventilation is clearly important. Here, we see giant ventilation tubes attached to the ceiling of the tunnel.

Due to a series of safety programs, injuries and accidents have been cut down significantly on the Gotthard Tunnel project.

There is a ventilation tunnel above the emergency station, designed to pull smoke out from burning trains. This is a connecting passageway to the ventilation tunnel.

The air pressure at the crossover sections could be so great that it could knock a train off the tracks. That's why there will be giant doors installed in front of the crossover sections that are designed to block the air flowing through, or to block fire or smoke. This shows where that giant door will be installed.

This is a weather door designed to minimize the heavy flow of air in sections of the tunnel that are still under construction. Sections will have these doors at both ends.