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Gotthard Base Tunnel

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The Gotthard Base Tunnel is currently under construction through the Alps Mountains in Switzerland. When completed, the tunnel will be 35 miles (56 km) long, running along the base of the mountain, 8,000 feet (2,438 m) below the highest peak and 1,600 to 1,800 feet (488 to 549 m) above sea level. In total over 13 million cubic yards (9.9 million cubic meters) of rock will need to be excavated.[1] It will be the world’s longest and deepest tunnel.

The tunnel is designed to house high speed trains to transport passengers and freight between Northern and Southern Switzerland. Passenger trains will reach speeds of 150 miles per hour (241.4 km) while freight trains will reach 100 miles (161 km) per hour.

The Gotthard Base Tunnel is designed to decrease traffic and pollution within Switzerland. Currently, the only way to travel through the Alps is on congested roads or very slow trains.[2] The new tunnel will allow people to travel from Milan, Italy to Zurich, Switzerland in 2.5 hours, which is faster than flying.[3]

Design and construction is being led by AlpTransit Gotthard Ltd., headquartered in Lucerne, Switzerland. The project’s chief engineer is Matthias Neuenschwander.

Each of the project’s five individual sites is being worked by a number of different companies including Strabag & Zublin Murer, Bilfinger Berger, Implenia, Fruitger, Pizzaroti, Alpine Mayreder Bau, CSC Impresa construzioni, Hochtief, Imlenia, and Impreglio.

The total cost of the project is an estimated US$ 11 billion[4], but has reportedly raised to $15 billion[5]. The projected completion date is 2015[6], but some sources claim construction delays have pushed the date back to at least 2018[7].

Contents

[edit] Construction History

[edit] Designing a Plan

The first idea for the Gotthard base tunnel was presented in 1947, but it was not until the late 1990s that the plan began to take its final shape.

In 1962 the Swiss Federal Department of Home Affairs developed some concrete plans for the Gotthard Base Tunnel. It outlined a double-track tunnel running through Switzerland straight from Amsteg to Giornico with access from two intermediate headings. The tunnel would be 28 miles (45 km) long with an overtaking track in the middle. The trains’ maximum speed would not exceed 125 miles (201 km) per hour.[8]

By 1971 aspects of the original plan were changed by the Committee for a Railway Tunnel through the Alps of the Swiss Federal Department of Environment, Transport, Energy and Communications. The committee felt the best solution was a two-track tunnel, possibly with some sections split into two separate single-track tunnels.

In 1995 the plans were altered again and would now be either a two-track tunnel with a service tunnel or two single-track tunnels, with or without a service tunnel.

The final design is a compromise of ideas. Two single-track tunnels without a service tunnel, but linked with connecting galleries about every 600 feet (183 m), each tunnel serving as an escape route for the other. Each tube will be 29.5 to 31 feet (9 to 9.4 m) in diameter.[9] The total length of all tunnels and shafts will be 95 miles (153 km).

The Gotthard Base Tunnel will replace an existing tunnel located much higher up in the Alps, which was only capable of handling three-truck freight trains of up to 2,000 tons while the new tunnel is designed to handle 4,000 tons of heavy freight trains.[10]

[edit] Tunnel Boring

The tunnel passes through mainly crystalline rock (strong igneous and metamorphic rock), which is favorable for tunneling.[11] However, some major sections have high overburden: from 3,200 to 6,500 feet (975 to 1,981 m).[12]

“The main danger is the risk of rock burst caused by the high overburden, the instability of rock edges and water inflow,” said Davide Fabbri, chief designer of the Gotthard project.[13]

The tunnel also passes over 90 different isolated short fault zones. This area is made of both soft and hard rock: a mixture of compact gneiss and overlapping strata of schistose rock and phyllite.

Construction is divided into five sites operating 24 hours a day, 365 days a year. The five sites are Ertsfeld, Amsteg, Sedrun, Faido, and Bodio. In total there will be 2,000 workers on the project.[14]

Most of the tunnel will be dug with tunnel boring machines (TBM); however, some explosives will also be used. There will be four TBMs in total, two for each tunnel, digging from both sides. Each machine costs approximately $23 million and was designed specifically for work in the Gotthard Base Tunnel.[15] Built by German manufacturer Herrenknecht, each TBM weighs 3,000 tons and is 1,300 feet (396 m) long. They produce five megawatts of power with a maximum excavation rate of 32 yards (29 m) per day.[16]

The TBMs are so gigantic that they had to be shipped in sections from Germany and assembled on site. Once underground these machines would not see the light of day for nearly 10 years.

However, these enormously powerful machines still require workers for them to operate to their full potential. Each TBM has 25 workers for every eight-hour shift. While the TBM digs, men work on top of the heavily vibrating machine attaching steel meshing to the tunnel walls to ensure debris does not fall onto them or the machine. (This machine rattles so violently it is like working during an earthquake all day.[17])

The workers have to drill anchors into the tunnel walls to secure the mesh screens. Meanwhile water is pumped into the anchor holes to keep the drill heads from overheating.

Six hours out of every day is spent on maintenance for the TBMs. The extreme vibrations cause parts to break. There are 20 to 25 workers whose job it is to ensure the machine is in proper working order and to change any dull cutterheads.

During this break in the boring, geologists spring into action collecting samples of the rock ahead. They need to understand the rock’s stability so they can warn the drilling team of any concerns. The geologists use long drills capable of retrieving samples 80 feet (24.4 m) in front of the cutting head. Using the TBM on unstable rock could be disastrous for the machine and the project.

An average of 7,000 tons of rock is excavated per day.[18] This rock material is pulled up by the cutterheads and dropped onto a conveyor behind the borehead. It is then transported to the rear of the TBM and either recycled or disposed. About 25 percent of the debris is converted into concrete aggregate. This aggregate is used to make a special type of concrete known as shotcrete. About 2,000 tons of shotcrete is used in the tunnels per day to seal and secure the walls.

Any contaminated debris (oil from TBMs, waste products from explosives, chemicals and heavy metals from shotcrete) is separated to ensure it is not stored in a conventional landfill.

All wastewater is treated to reduce acidity, neutralize chemicals and separate oils. The water is also cooled, if necessary, before being introduced to a river or being recycled for industrial use or as a liquid for the tunnel cooling system.[19]

[edit] The Tunnel Collapses

While digging, the TBM named “Gobi II” reached unstable rock that collapsed on top of it. The rock had become extremely brittle after years of wear from mountain water. It tumbled on to the machine like sand in an hourglass. [20] The machine was only four miles (6.4 km) in, where it remained stuck for several months because TBMs are incapable of moving in reverse.

In order to save Gobi II, the engineers decided to blast two access tunnels from the second tunnel. One access tunnel would attack the borehead from the front while the other would attack from the side. Their reasoning was that if they simply attacked from the front, the rock could collapse on the rescue workers. The side access tunnel would allow workers to inject concrete into the crumbled mass of rock on the TBM making it solid and safe enough to attack from the front.

[edit] Explosives

Sometimes explosives are chosen in favor of the TBM because of the type of rock. In these cases a giant octopus-like drilling machine called “the Jumbo” is used to prepare the rock face. It is capable of drilling four holes simultaneously. Using laser guided technology the drill heads can line up the exact drilling spot with pinpoint accuracy. These holes need to be exact in order for the explosives to work correctly.

A blasted hole is more difficult to support than a bored hole because it does not cut as cleanly as a TBM.[21]

[edit] Maintaining the Pressure

"We've got two-and-a-half kilometers of Alps above us," explains engineer Albert Schmid. "That means millions and millions of cubic meters of earth pressing down on us, that increases the pressure and the temperature." [22]

The project engineers are in a constant battle to keep the pressure of the Alps from crushing the tunnel. Their first attempt was to use the strongest steel available, but it was not strong enough. They eventually found the solution in a German factory, Bochumer Eisenhutte, who had developed steel reinforcements specially designed for tunnels.

Instead of using stiff, strong, and rigid supports they made flexible beams with moving parts held together with clasps. Small sections of the beam were under varying pressure capable of collapsing into itself, shrinking without buckling. These beams were put in place where they would sit for two months settling under the pressures of the mountain. Once completely settled they would be concreted into place.

[edit] Battling the Heat

For workers inside the tunnel conditions can be extremely harsh. On a good day the tunnel is 80 degrees Fahrenheit with 70 percent humidity. On a bad day the temperatures can reach 115 degrees Fahrenheit with close to 100 percent humidity.

Ventilation is of the utmost importance. There are nine-mile long ventilation tunnels designed to bring cool, fresh air into the tunnel. The company Poyry Infra AG is responsible for designing the ventilation system. If a fire breaks out in one of the main railroad tubes, the vent system raises the air pressure in the unaffected tube to keep it clear of smoke. The people in the tube with the fire will then move to the pressurized tube through emergency stations or cross passages.[23]

However, even on bad days, in almost unbearable conditions, workers are often able to operate at peak performance (one day they excavated approximately 9,000 tons of material).[24]

[edit] Solution Creates a Problem

While the shotcrete provides stability to the tunnel walls, its application requires attention to detail. Too little and it may not hold, while too much can make the tunnel too thin. Extra special attention is needed for parts of the tunnel being excavated underneath a flowing riverbed.

In instances where too much shotcrete is used, workers are required to remove excess material away to ensure the tunnel is consistently wide throughout.

Also, while the TBMs allow the tunnel to be excavated quickly they can often leak oil, which if not properly cleaned up can pollute Swiss water sources. Therefore workers are responsible to ensure the oil is cleaned immediately before it can cause any problems.

[edit] Rail Track Installation

The rail infrastructure within the tunnel will be constructed by Transtec Gotthard Consortium, which is comprised of a number of Swiss and German companies. Installation is set to begin in the south portal in 2009 and the north portal in 2010. It is scheduled to take seven years to complete. The contract is worth US$1.6 billion.[25]

[edit] Equipment Used

[edit] References

  1. Discovery Channel. Extreme Engineering: Gotthard Tunnel, 2006
  2. Discovery Channel. Extreme Engineering: Gotthard Tunnel, 2006
  3. Foulkes, Imogen. Swiss dig world's longest tunnel. BBC News, March, 2007. (accessed: 2008-09-25)
  4. Additional Investments for the AlpTransit Gotthar Project. AlpTransit, 2008-09-25.
  5. Foulkes, Imogen. Swiss dig world's longest tunnel. BBC News, March, 2007. (accessed: 2008-09-25)
  6. Fabbri, Davide. The Gotthard Base Tunnel: Project Overview. Lombardi Engineering Ltd., August, 2004. (accessed: 2008-09-25)
  7. Foulkes, Imogen. Swiss dig world's longest tunnel. BBC News, March, 2007. (accessed: 2008-09-25)
  8. The Gotthard Base Tunnel: 50 years of planning. AlpTransit, 2008-09-25.
  9. Fabbri, Davide. The Gotthard Base Tunnel: Project Overview. Lombardi Engineering Ltd., August, 2004. (accessed: 2008-09-25)
  10. Megabuilders: The Gotthard Base Tunnel. Discovery Channel, 2008-09-25.
  11. Fabbri, Davide. The Gotthard Base Tunnel: Project Overview. Lombardi Engineering Ltd., August, 2004. (accessed: 2008-09-25)
  12. Fabbri, Davide. The Gotthard Base Tunnel: Project Overview. Lombardi Engineering Ltd., August, 2004. (accessed: 2008-09-25)
  13. Fabbri, Davide. The Gotthard Base Tunnel: Project Overview. Lombardi Engineering Ltd., August, 2004. (accessed: 2008-09-25)
  14. Discovery Channel. Extreme Engineering: Gotthard Tunnel, 2006
  15. Discovery Channel. Extreme Engineering: Gotthard Tunnel, 2006
  16. Discovery Channel. Extreme Engineering: Gotthard Tunnel, 2006
  17. Discovery Channel. Extreme Engineering: Gotthard Tunnel, 2006
  18. Discovery Channel. Extreme Engineering: Gotthard Tunnel, 2006
  19. Fabbri, Davide. The Gotthard Base Tunnel: Project Overview. Lombardi Engineering Ltd., August, 2004. (accessed: 2008-09-25)
  20. Discovery Channel. Extreme Engineering: Gotthard Tunnel, 2006
  21. Discovery Channel. Extreme Engineering: Gotthard Tunnel, 2006
  22. Foulkes, Imogen. Swiss dig world's longest tunnel. BBC News, March, 2007. (accessed: 2008-09-25)
  23. Buchmann, Reto. A Swiss Engineering Team Designs a Ventilation System for the World's Longest Rail Tunnel. The MathWorks, June, 2007. (accessed: 2008-09-25)
  24. Discovery Channel. Extreme Engineering: Gotthard Tunnel, 2006
  25. AlpTransit and Transtec Gotthard Consortium to build base tunnel. CBROnline, 2008-09-25.