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Laerdal Tunnel

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The Laerdal Tunnel, located in Norway, is part of the country’s new main highway connecting Oslo and Bergen. The tunnel links Norway’s two largest cities, Aurland and Laerdal, over a span of 15.2 miles (24.5 km); it is the longest road tunnel in the world.[1]

The tunnel, constructed over the course of five years, was officially opened on November 27, 2000, and its total cost was approximately US$125 million.[2]

Since the tunnel’s opening in 2000, Norway has experienced an increase in tourism, as the unique passageway attracts people to drive through the area.

Contents

[edit] History

[edit] The Need for a Better Route

The construction of the Laerdal Tunnel was initiated following a decision by the Norwegian government in June 1992.[3] The parliament was concerned with the roadways in the country, especially in the western area. A driver’s commute at the time included driving on narrow roads, over fjords, and through mountains—some up to 5,935 feet (1,809 km) high.[4] These mountain passes were often closed in the winter season due to heavy snowfall. The need to link regions more effectively and reliably in order to reduce hazards, travel time, and transportation costs for businesses, was recognized. In March 1995, three years after the initial decision to build, construction of the ferry-free sub-mountain shortcut commenced.

[edit] Breaking Through the Rock

The Laerdal Tunnel was constructed using the drill and blast tunneling method. Rock was removed using explosives, computer-controlled drilling jumbos, and traditional drilling methods.

[edit] Drilling Jumbos

Computer controlled methods were integral in the operation, as a high level of precision was required to drill more than 6.2 miles (10 km) into the rock lying over 0.6 miles (1 km) under a mountain.[5] The jumbos were outfitted with a computer that could position drilling equipment automatically with the use of lasers. Each drilling jumbo comprised of three automatic hydraulic drills. For each intended blast, approximately 100 holes 17 feet (5.2 m) deep and 1.7 to two inches (45 to 51 mm) in diameter were drilled. During construction, drilling took place at three sites simultaneously to expedite operations.

[edit] Rock-blasting Explosives

For each hole drilled by drilling jumbos, a detonator was placed at the bottom inside a small stick of dynamite. An explosive known as anolit, Norway’s most commonly used tunnel-blasting explosive, was used to clear the areas. Each blast made use of 1,102 pounds (500 kg) of explosives and ate through 16 feet (5 m) of rock.

By the time breakthrough was made in September 1999, about 5,000 blasts had been set off. In total, approximately 3.3 million cubic yards (2.5 million m3) of rock were excavated from the tunnel.[6]

[edit] Stabilizing the Rock Walls

Though most of the rock in the area through which the tunnel would be drilled was solid, certain areas comprised weak or cracked material. Rock fall was caused by the stresses of drilling during the initial stages of construction—plunging a total of 1,308 cubic yards (1,000 m3) of rock into the tunnel’s passageway. In response, the workers filled the hole in the ceiling with concrete, and drilled a new tunnel through the fallen debris.

Precautions had to be taken to prevent falling rocks due not only to cracks, but also as a result of the phenomenon known as rock burst. This occurs due to the intense pressure above the tunnel, sometimes resulting from up to 4,593 feet (1.4 km) of rock sitting directly on top of it. This pressure compromises the tunnel’s stability, leading to loosening and falling of small to large blocks of stone when the area is blasted.

After each blast of explosive, debris was cleared by a hydraulic scalar attached to an excavator. Following excavation and subsequent manual scaling, the tunnel’s roof and walls were reinforced with galvanized steel bolts 8.2 to 16.4 feet (2.5 to 5 m) long to drive the stress deeper into the rock. Additional reinforcements were made fiber-reinforced shotcrete, a concrete or mortar substance pneumatically applied at a high velocity, in order to bind rock surfaces together. In total, the tunnel’s surface was reinforced with a total of 200,000 rock bolts and 147,637 feet (45 km) of reinforced shotcrete.[7]

[edit] Removing Materials

Wheel loaders were used in the tunnel to lift excavated debris and load it into dump trucks. The trucks would then transport the materials out of the tunnel. Dump trucks and other transport vehicles ran on permanent paved roads that were built within the tunnel to facilitate smooth transportation, improving efficiency and decreasing polluting emissions in the work area.

Excavated rocks were transported and deposited in Tynjadal, a side valley approximately five miles (8 km) east of Laerdal. Additional rock debris has since been used on the Aurland side of the tunnel in various projects such as the construction of part of a new highway between Flam and Aurlanda, as well as a pedestrian and bicycle path stretching along the Aurland fjord from Flam to Otternes.

In order to efficiently remove materials from the tunnel without disturbing the region’s culturally and economically important landscape and farmland, over half of the tunnel was built from a 1.3-mile (2.1-km) access tunnel in Tynjadal, rather than building from either end. This access tunnel enabled crews to avoid damage to Laerdael’s main valley and waterways. Though costly, this access tunnel considerably shortened construction time, while avoiding inconvenience to the surrounding population. The access tunnel would also become an integral part of the tunnel’s ventilation system.

[edit] Air Purification

The Laerdal Tunnel is longitudinally ventilated: polluted air is extracted through the ventilation system in the access tunnel. The tunnel includes two larges fans to draw impurities through a treatment plant located approximately 5.9 miles (9.5 km) from the Aurland opening. The cleaning plant, located in a 328-foot (100-m) cavern, purifies passing air with electrostatic and carbon filters, removing polluting elements such as dust and nitrogen dioxide, maintaining safe air quality in the tunnel even during times of traffic congestion. The Laerdal Tunnel is unique in that it is the first to include its own air purification plant.[8]

[edit] Accident Prevention

Since the drive through the 15.2-mile (24.5 km) long Laerdal Tunnel takes approximately 20 minutes, project officials recognized the importance of the tunnel’s design. Psychologists, led by Gunnar Jenssen of the University of Trondheim, worked with the Norwegian Public Roads Administration to decide how to keep motorists engaged and reduce mental strain over the course of the long ride through the tunnel.

[edit]

A unique element in the Laerdal Tunnel is the inclusion of three large caverns, or “mountain halls,” spaced 3.7 miles (6 km) apart. In contrast to the white light used in the tunnel’s main expanse, these mountain halls are illuminated with blue and yellow light, giving drivers the impression that they are driving into daylight every 3.7 miles (6 km). The golden-lit floors in these caverns provide the illusion of a sunrise. The intention of the mountain halls is to include enough variation that motorists will remain attentive and awake.

[edit] Further Safety Features

The Laerdal Tunnel also features a loud rumble strip near the center of each lane, to alert dozing motorists, avoiding possible head-on collisions. Other security measures include emergency phones every 820 feet (250 m), fire extinguishers every 420 feet (125 m), and stop lights and signs that illuminate and warn motorists to turn and drive out of the tunnel in the event that an emergency phone has been used.

The tunnel includes 15 areas wide enough for buses and semi-trailers to turn around in the event of a crisis, as well as “emergency niches” every 1,640 feet (500 m).

Surveillance of the tunnel is undertaken through connections to security centers in Laerdal and Bergen. Moreover, the area is monitored through photo inspection and the tracking of the number of cars passing through the tunnel. There is staff located in a control room to monitor pollution levels in the tunnel. In the event of an accident, fans are employed, sucking smoke up a 1.2-mile (2-km) chimney.

Phone channels for emergency personnel—police, fire departments, and hospitals—are also included. The use of cell phones and radios are facilitated with the inclusion of special wiring throughout the tunnel.

[edit] Equipment Used

[edit] Unique Facts

  • Longest road tunnel in the world.
  • A couple exchanged marriage vows in the mountain hall in the center of the tunnel.[9]
  • First tunnel to include its own air purification plant.

[edit] References

  1. Brekke, Arne. The world's longest road tunnel: Laerdal - Aurland. Bergen Guide, 2008-09-25.
  2. Brekke, Arne. The world's longest road tunnel: Laerdal - Aurland. Bergen Guide, 2008-09-25.
  3. Laerdal Tunnel. Engineering.com, 2008-09-25.
  4. Brekke, Arne. The world's longest road tunnel: Laerdal - Aurland. Bergen Guide, 2008-09-25.
  5. Laerdal Tunnel. Engineering.com, 2008-09-25.
  6. Laerdal Tunnel. Engineering.com, 2008-09-25.
  7. Laerdal Tunnel. Engineering.com, 2008-09-25.
  8. Brekke, Arne. The world's longest road tunnel: Laerdal - Aurland. Bergen Guide, 2008-09-25.
  9. Norway to open world's longest road tunnel. CNN.com, November, 2000. (accessed: 2008-09-25)