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Mont Cenis Tunnel

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The Mont Cenis Tunnel, also known as the Frejus Rail Tunnel, spans 8.5 miles (13.7 km) through the European Alps, connecting Modane, France and Bardonecchia, Italy. Construction of the tunnel began in August 1857 from Italy, and in December of the same year from France. It was completed on December 25, 1870, and opened to traffic on September 17th, 1871, more than 10 years ahead of schedule.

Construction of the tunnel was a great challenge, accomplished in spite of the snowy and glacial conditions of the Alps, combined with the hard, rocky formations of the mountains. New technology was favored considerably, ensuring not only the tunnel's successful construction, but also its early completion. Such technology included compressed air and pneumatic rotary drills.

The project, spearheaded by Germain Sommellier, cost £3,000,000 sterling—the equivalent of £200 per yard.

The Mont Cenis is one of the oldest and longest tunnels in the Alps. [1]

Contents

[edit] Construction History

The idea to build the tunnel was conceived in 1832 by M. Medail, a Piedmontese, who, 10 years later, developed a plan for the government to construct a tunnel. Two engineers, Maus and Sismonda, were appointed to investigate the feasibility of constructing a tunnel. The project met their approval four years later.

There were some initial concerns regarding moving forward with the construction project. These included how far beneath the summit of the mountain construction should run in order to prevent the shafts from sinking. In addition, the further underground the workers were sent, the more difficult it would become to provide suitable breathing air for them. Because it was so far underground, the use of steam power and steam engines was decided against, as it required fire and abundance of air, coal, and water, all of which could not be adequately provided.

[edit] Compressed Air

In 1850 three Italian engineers, Sommellier, Grandis, and Grattoni, decided on using compressed air to tackled the excavation of a tunnel in Mont Cenis. Power in the form of compressed air, proved to be beneficial because air, when compressed to one-sixth of its original state, could exert a force of 84 pounds per square inch (579 kPa). This was considerably more powerful than what could conveyed by a steam engine at that time. The power was directed onto a focal point with the use of levers, pulleys, and cogs.

The use of compressed air was made possible by a water wheel consisting of iron columns and several hollow tubes that opened by a valve into the tank. The wheel would collect water and push it up into the tube, a motion that would force air into the tank. When the water reached the surface of the tube, the valve at the bottom would close and another valve at the top would open, allowing air into the tank. The current of the river turned the wheel, bringing water into the pipe, which condensed the air inside the eight-inch (20-cm) diameter pipes. While the water was condensing in the pipes, the cylinders rose and opened the supply valve, which closed when they fell. [2]

[edit] Deciding on Direction

During the tunnel’s construction, there were many things to consider, one of which was the direction of the tunnel. The engineers also set out to correct the line of the tunnel as the horizontal axis had to be fixed. A line was marked from the summit of the Great Vallon, 2.08 miles (3.3 km) above the sea. The line was so securely fixed that it could not veer off a foot (0.3 m) to the right or left without resulting in failure; a compass was used to ensure that the precise measurements didn’t lead the crew off the line.

Another difficulty was in getting the two portions of the tunnel to not only meet each other in both directions (east and west), but to meet at the same point in vertical elevation. This required that excavation at each side must be precise. This was a difficult process, but on Christmas day in 1870, crews experienced success when both excavated sides met each other almost to an inch (2.5 cm).

[edit] Hand Vs. Machine

Compressed air was not the only new technology to be used for the construction of this tunnel. In 1855, an English engineer by the name of Mr. Bartlett, invented a steam-driven drill for the purpose of coal mining in England. Even though a steam-drill could not be used in the Apline tunnel, it gave Sommellier the idea to combine the invention of the steam drill with that of compressed air. The result was a pneumatic drill that could bore its way through the hard rock formation of the Alps. The Italian government, however, carried out a considerable amount of tunnel excavation without the use of machinery at this point in 1857.

The construction of the tunnel was carried out by manual labor until 1861. After that time, machinery was employed, but its use caused delays in the operations. In 1861, machinery was used for only 209 days and progress was slow, with the tunnel advancing only 18 inches (46 cm) per day. The engineers, however, corrected the problems associated with the machinery and put it back to work in 1862, during which time the machines successfully completed 325 working days, accomplishing an average of three feet, nine inches (1 m, 13 cm) per day. However, the use of compressed air machinery required more time and it was an additional two years before this was made available at the disposal of the workers.

[edit] Use of Pneumatic Rotary Drills (Perforators)

When air compression machinery was made available, it was able to exert a pressure similar to that of 90 pounds per square inch (621 kPa). The rotary drill, operated pneumatically, took just two men to use: one man to turn the drill, and the other to give the blow. The compression machine achieved pressure by pushing a column of water 160 feet (49 m) high, receiving it through valves and compressing it through condensed air. After the compressed air reached the cylinders of the boring tools, it produced a cooling condition in the air, which worked well for the workers who were already experiencing warmth from being underground. The escaping air provided ventilation for the workers and facilitated boring and excavation that other machinery would not have been able to provide. This method was especially effective because it removed the need for hot lights, explosions, and gunpowder that would have normally been employed. Such use would have been to the detriment of the project and the health of the workers.[3]

The perforators used compressed air that was transmitted through a small piston inside a cylinder. The rod of the piston was attached to a jumper. When the air was transmitted to the piston, it would propel the jumper to strike the rock and then rebound the tool back into the opening of the valve, which also received compressed air.

The perforator operated in rapid motion, striking the formation four or five times a second (as much as 200 to 300 times a minute). During this process, water was pushed into the holes to remove cuttings and debris. Several of these perforators or pneumatic rotary drills were used, mounted on frames, and supported by wheels.

The jumpers would be directed into the formation and could bore about 2.5 feet (0.76 m) in approximately 45 minutes. After sets of holes were bored, the cylinders were replaced by another set of cylinders and more drilling was undertaken. Seven or eight hours and 80 holes later, the next step was executed, consisting of dislodging rock by conveying water and air through tubes at the tunnel’s entrance. The perforators were then removed from the holes so that the worker could place explosive equipment inside them. After the explosion, compressed air was used to remove the smoke and gas produced as a result. Wagons carried away bits of rock and stones. In addition, the floors were leveled and a tramway extended so the drilling machinery could advance forward.

[edit] The End of the Line

After four years of using pneumatic drills, it was estimated that the project might be complete by 1875. In fact, it was complete on December 25, 1870. The drill, perforator No. 45, drilled a hole from Italy to France, through rock that was four yards (3.7 m) thick. When it was completed, Fourneaux, the northern entrance, reached 3,801 feet (1,159 m) above sea level and Bardonneche, the southern entrance, reached 4,236 feet (1,291 m) above sea level. The summit of the tunnel reached 4,246 feet (1,294 m) and the highest point of the mountain, extending vertically above the tunnel, reached more than 9,500 feet (2,896 m). [4]

Materials used to construct the tunnels lining included brick and stone, which were laid in arches and connected to the railway.

Between 1857 and 1860 the work was carried out by hand, excavating 5,400 feet (1,646 m). From 1861 to 1870, 34,734 feet (10,587 m) was excavated by machinery; a large portion of this—4,000 feet (1,219 m)—was excavated in May 1865. The most difficult period of boring took place during April 1866 when machines were boring through quartz, a hard rock. The quartz's existence resulted in the boring of not more than 35 feet (11 m). [5]

Today, the Mont Cenis Tunnel remains an important link between France and Italy. In addition to the tunnel, the Frejus Road Tunnel has been added, to provide means for cars and trucks. The Frejus Road Tunnel project began in 1974 and was completed by 1980.

[edit] Refurbishment/Recent Projects/Renovations

The Lyon Turin Ferroviaire project plans to install a high-speed rail tunnel between France and Italy sometime in the future.

[edit] Equipment Used

[edit] Unique Facts

  • On December 25, 1870, construction workers from both sides (France and Italy) shook hands as they met each other at the halfway point.
  • Construction was projected to take 25 years but was completed in 14 years. The early completion was in large part to new construction techniques such as pneumatic drilling.
  • The railway tunnel was used to transport mail from England to India.
  • The tunnel was 15 yards (14 m) longer than initially expected.
  • Upon completion of the tunnel, it took a train 25 minutes to travel from one side of the tunnel to the other.
  • As many as 4,000 workers were employed to work on the tunnel at a given time.
  • The total horsepower of the machinery used amounted to 860.
  • The tunnel opened on September 17, 1871. It is one of the oldest and largest tunnels of the Alps. [6]

[edit] References

  1. Mont Cenis. Catskill Archive. 2008-10-20.
  2. Mont Cenis. Catskill Archive. 2008-10-20.
  3. Mont Cenis Tunnel-Rock Boring. Today in Science. 2008-10-20.
  4. Mont Cenis Tunnel-Rock Boring. Today in Science. 2008-10-20.
  5. Mont Cenis. Catskill Archive. 2008-10-20.
  6. Mont Cenis Tunnel-Rock Boring. Today in Science. 2008-10-20.