Tunnel Engineering

7) “Tunnel Engineering”

(Date of Publication = 12 March, 2013)

Tunnel Engineering

Tunnel is an underground passageway or a tube hollowed through soil or stone, completely enclosed except for openings for entrance and exit, commonly at each end. Tunnels are used for mining, as passageways for trains and motor vehicles, for diverting rivers around dam sites, for housing underground installations such as power plants, and for conducting water. Secret tunnels have given entrance to or escape from an area, such as the Cu Chi Tunnels or the smuggling tunnels in the Gaza Strip which connect it to Egypt. Tunnel Engineering

The origin of tunnel building is disputed. The Egyptians built tunnels as entrances to tombs. The ancient Greeks and Romans built tunnels for carrying water and for mining purposes; some of the Roman tunnels are still in use.  Ancient civilizations used tunnels to carry water for irrigation and drinking, and in the 22nd century BC the Babylonians built a tunnel for pedestrian traffic under the Euphrates River. The Romans were skilled tunnel builders; they built aqueduct tunnels through mountains by heating the rock face with fire and rapidly cooling it with water, causing the rock to crack. The introduction of gunpowder blasting in the 17th century marked a great advance in solid-rock excavation. Tunnel Engineering

Engineers always start a tunnel project with a comprehensive investigation of ground conditions by collecting samples from boreholes and by other geophysical techniques. An informed choice can then be made of machinery and methods for excavation and ground support, which will reduce the risk of encountering unforeseen ground conditions. In planning the route the horizontal and vertical alignments will make use of the best ground and water conditions. Tunnel Engineering

For tunnel design following requirements must be fully satisfied: stability of tunnel openings, protection of adjacent or overlying structures and ability of the tunnel to perform over the intended life.  Tunnels are dug in types of materials varying from soft clay to hard rock. The method of tunnel construction depends on such factors as the ground conditions, the ground water conditions, the length and diameter of the tunnel drive, the depth of the tunnel, the logistics of supporting the tunnel excavation, the final use and shape of the tunnel and appropriate risk management. Tunnel Engineering

Following are the basic types of tunnel construction in common use:

a. Cut and Cover Tunnelling – Cut and cover tunnelling is a common and well-proven technique for constructing shallow tunnels. The method can accommodate changes in tunnel width and non-uniform shapes and is often adopted in construction of underground stations. Tunnel Engineering

b. Drill and Blast – This tunnelling method involves the use of explosives. Drilling rigs are used to drill blast holes on the proposed tunnel surface to a designated depth for blasting. Tunnel Engineering

c. Bored Tunnelling by Tunnel Boring Machines (TBM) – Bored tunnelling by using a Tunnel Boring Machine (TBM) is often used for excavating long tunnels. The TBM may be suitable for excavating tunnels which contain competent rocks that can provide adequate geological stability for boring a long section tunnel without structural support. Tunnel boring machines (TBMs) and associated back-up systems are used to highly automate the entire tunnelling process, reduces tunnelling costs. Tunnel Engineering

d. Sequential Excavation Method – This method is also known as the New Austrian Tunnelling Method (NATM). The excavation location of a proposed tunnel is divided into segments first. The segments are then mined sequentially with supports. This method is relatively slow but is found useful in areas where existing structures such as sewer or subway could not be relocated. Tunnel Engineering

A tunnel is relatively long and narrow; in general the length is more (usually much more) than twice the diameter. Railroad transportation in the 19th–20th century led to a tremendous expansion in the number and length of tunnels.  World’s longest and famous tunnels are as follows;

  • The Gotthard Base Tunnel will be the longest rail tunnel in the world at 57 km.  It will be totally completed in 2017.
  • The Seikan Tunnel in Japan is the longest undersea rail tunnel in the world at 53.9 km, of which 23.3 km is under the sea.
  • The Channel Tunnel between France and the United Kingdom under the English Channel is the second-longest rail tunnel, with a total length of 50 km, of which 39 km is under the sea.
  • The Lötschberg Base Tunnel opened in June 2007 in Switzerland was the longest land rail tunnel, with a total of 34.5 km.
  • The Laerdal Tunnel in Norway from Laerdal to Aurland is the world’s longest road tunnel, intended for cars and similar vehicles, at 24.5 km.
  • The Zhongnanshan Tunnel in People’s Republic of China opened in January 2007 is the world’s second longest highway tunnel and the longest road tunnel in Asia, at 18 km.

Unfortunately Pakistan lack expertise in the field of tunnel engineering, though tunnels for vehicular road traffic and rail traffic are considered as the safest and fastest system in developing worlds. In Pakistan, there are only three tunnels: Tunnel Engineering

The Lowari Tunnel is an 8.6 km long tunnel located in the NWFP province of Pakistan between Dir and Chitral District. This tunnel will reportedly reduce the current 14-hour drive from Chitral to Peshawar by half. A South Korean construction company, SAMBU, has been assigned the work on the tunnel. Cost of the project is Rs.8 billion ($133 million US). Tunnel Engineering

The Kohat Tunnel is a 1.9 km long road tunnel located in the NWFP province of Pakistan. Constructed with Japanese assistance, it is also known as the Pak-Japan Friendship Tunnel. Construction on the tunnel began in 1999, and was opened to traffic in June 2003. As part of the developing Indus Highway system, the tunnel serves as a shorter, alternate route to the Kohat Pass, situated between the cities of Peshawar and Kohat. Tunnel Engineering

The Khojak Tunnel is one of the longest tunnels in South Asia, was fourth longest tunnel in the world at the time of built in 1891 and still the longest in Pakistan. It carries a railway track and it is 3.912 kilometres long located in Qilla Abdullah district of Balochistan province of Pakistan. It is located 1,945 meters above sea level. It was featured on the old Rs. 5 banknote. Tunnel Engineering

Tunnel construction is one of the most compl­ex challenges in the field of civil engineering but these challenges haven’t stopped engineers from dreaming up even bigger and bolder ideas. We all are aware of the fact that there are lots of risks involved but tunnel Engineers take such risks in the hope of favorable outcomes. Many tunnels are considered as technological masterpieces and governments have honored tunnel engineers as heroes.  In modern tunneling, steel is generally used and tunnels are designed and built to enrich skylines and provide fast, efficient transportation through any obstacle. Tunnel Engineering

If Mughals can made remarkable construction from early 15th century to early 18th century then why today we are afraid of adopting modernized tunnel techniques for building this unique structure .

Sara Shahid
Civil Engineer

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