Read the text and make a list of tunneling terminology.

A tunnel is a man-made horizontal underground passageway created by excavation through a hill or under a road or river etc., especially for a railway or road to pass through. In general, tunnels are at least twice as long as they are wide. In addition, they should be completely enclosed on all sides and safe at the openings at each end. Some civic planners define a tunnel as 0.16 km in length or longer, while anything shorter than this should be called a chute. Tunnels underwater are now commonly built by the use of an immersed tube: long, prefabricated tube sections are floated to the site, sunk in a prepared trench, and covered with backfill.

It is probable that prehistoric people seeking to enlarge their caves did the first tunnelling. All major ancient civilizations developed tunneling methods, and a brick-lined pedestrian passage some 900 m long was built in Babylonia about 2160 BC under the Euphrates River. The notable Bridgewater Canal Tunnel was built in England in 1761. With the introduction of railroads about 1830, the new form of transport produced a huge increase in tunneling.

Tunnels have many uses: for transportation—including road vehicles, trains; for subways, and canals; for mining ore, and for conducting water and sewage. They are used for such things as underground hydroelectric-power plants, pumping stations, pedestrian passages, etc. Tunnels are the most complicated engineering structures and cost a lot of money. At the time, the Channel Tunnel was being built, it was the most expensive construction project ever conceived. It took $21 billion to complete the tunnel. That is 700 times more expensive then the cost to build the Golden Gate Bridge! For all underground work, difficulties increase with the size of the opening, and are greatly dependent upon weaknesses in the natural ground and the extent of water inflow.

Tunnel classification involves several factors.

Factor 1. (tunnel function):

1.1. Transportation tunnels. The central part of a rapid transit network is usually built in tunnels. To allow non-level crossings, some lines run in deeper tunnels than others.

1.2. Mine tunnels.

1.3. Service line tunnels. (For conducting water and sewage, electric and vision cable maintenance in large cities).

1.4. Waterpower or hydraulic tunnels.

1.5. Tunnels for special military needs.

Transportation tunnels may be classified in the following way:

Factor 1.1 (mode of transport):

1.1.1. Railway tunnels.

The Channel Tunnel, 50 km long, also called Euro tunnel, is a rail tunnel that runs beneath the English Channel. It consists of three tunnels: two for rail traffic and a central tunnel for services and security. The tunnel runs between Folkestone, England, and Sangatte (near Calais), France, and is used for freight and passenger traffic. Passengers can travel either by ordinary rail coach or within their own motor vehicles, which are loaded onto special rail cars. Trains can travel through the tunnel at speeds as high as 160 km per hour; the trip takes about 35 minutes.

1.1.2. Motorway tunnels.

1.1.3. Pedestrian tunnels.

1.1.4. Metro tunnels.

1.1.5. Navigation tunnels.

Factor 2. (tunnel location):

2.1. Flat ground tunnels.

2.2. Mountain tunnels.

2.3. Sub aqueous (underwater) tunnels or sunken-tube tunnels.

The Mersey Tunnel in Great Britain is the longest sub aqueous tunnel and links Liverpool (north) with Birkenhead (south). The workers began tunnelling from both banks and the breakthrough took place in the middle of the river beneath the riverbed. There are several tunnels beneath the Thames in London, which provide railway links (the twin Blackwall Tunnels – Southbound and Northbound) and pedestrian walkways (the Greenwich Tunnel) under water. In 1825, the Wapping-Rotherhithe Tunnel was driven through clay under the Thames River. The tunnel was constructed in horseshoe sections and brick-lined. It was the first sub aqueous tunnel in the world and was for many years the largest soft-ground tunnel. It has been used as a part of the Tube since 1913 and underwent refurbishment in the late 1990s.

Factor 3. (construction method):

3.1. Tunnels built by the cut-and-cover method.

3.2. Rock tunnels, built by the cutting method.

3.3. Shield driven tunnels.

Tunnelling under rivers was considered impossible until M. Brunel developed the protective shield in England. Jacks propel a shield forward and permanent lining segments are erected under protection of the shield tail.

Factor 4. (tunnel laying depth):

4.1. Shallow-lying tunnels (up to 10 m deep).

4.2. Deep-laid tunnels (over 10 m deep).

Factor 5. (shape of the tunnel cross-section):

5.1. Rectangular section tunnels.

5.2. Circular section tunnels (strongest shape).

5.3. Horseshoe section tunnels (flat bottom provides roadway).

Some tunnels are double-decked, for example the Eastern Harbour Crossing in Hong Kong, where roads and rails (the MTR metro) occupy different decks of the tunnel. The vehicles using a tunnel can outgrow it, requiring replacement or enlargement.

Exercises: