Unit 6 Tunnel

1. Introductio

1.1 Read the text title and hypothesize what the text is about. Write down your hypothesis.

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1.2 What do you know concerning this issue? List your ideas in the table left column “I know”.

I know	I have learnt

3. If you know answers to these questions write them down in the space given after each question.

1	What tunneling technique was used in Babylon ?
2	Who developed the models of a tunneling shield in the 19-th century?
3	What materials are used in tunnels?
4	When were the first drilling jumbos invented?
5	What factors is a tunnel’s construction method determined by?
6	How many methods are used to remove material from the tunnel track?
7	What is the longest person-carrying tunnel?

3. Circle in the list the words and expressions you know. Write down their translation in the table and calculate the percentage of your lexical competence.

1	person-carrying tunnel		9	prefabricated section
2	to grind away		10	gun powder
3	tunnel blasting		11	eventually
4	cutting devices		12	rubber seal
5	digging tools		13	to mount
6	to fill voids		14	tunneling shield
7	a deep trench		15	box-shaped tube
8	a pilot tunnel		16	lining materials

A tunnel is an underground or underwater passage that is primarily horizontal. Relatively small-diameter ones carry utility lines or function as pipelines. Tunnels that transport people by rail or by automobile often comprise two or three large, parallel passages for opposite-direction traffic, service vehicles, and emergency exit routes.

The world's longest tunnel carries water 105 mi (170 km) to New York City from the Delaware River. It is drilled through solid rock. The Seikan Tunnel in Japan is the longest person-carrying undersea rail tunnel in the world at 53.9 km (33.5 mi), of which 23.3 km (14.5 mi) is under the sea. It is between Japan's two largest islands, Honshu and Hokkaido. The Gotthard Base Tunnel will be the longest rail tunnel in the world at 57 km (35 mi). It will be totally completed in 2017

One of the most anticipated tunnels was the Channel Tunnel. Completed in 1994, this tunnel (between France and the United Kingdom under the English Channel) is the second-longest, with a total length of 50 km (31 mi), of which 39 km (24 mi) is under the sea.

History. The origin of tunnel building is disputed. Tunnels were hand-dug by several ancient civilizations in the Indian and Mediterranean regions. In addition to digging tools and copper rock saws, fire was sometimes used to heat a rock obstruction before dousing it with water to crack it apart. The cut-and-cover method—digging a deep trench, constructing a roof at an appropriate height within the trench, and covering the trench above the roof (a tunneling technique still employed today)—was used in Babylon 4,000 years ago. 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. One of the first notable tunnels in Great Britain was part of the Grand Trunk Canal. It was nearly 2 mi (3.2 km) long and was completed in 1777.

The first advance beyond hand-digging was the use of gunpowder to blast a 515-ft (160-m) long canal tunnel in France in 1681. Nitroglycerine (stabilized in the form of dynamite) replaced the less powerful black powder in tunnel blasting. Steam and compressed air were used to power drills to create holes for the explosive charges.

Between 1820 and 1865, British engineers Marc Brunel and James Greathead developed several models of a tunneling shield that enabled them to construct two tunnels under the Thames River. A rectangular or circular enclosure (the shield) was divided horizontally and vertically into several compartments. A man working in each compartment could remove one plank at a time from the face of the shield, dig ahead a few inches, and replace the plank. When space had been dug away from the entire front surface, the shield was pushed forward, and the digging process was repeated. Workers at the rear of the shield lined the tunnel with bricks or cast iron rings.

During the 19th and 20th centuries, the development of railroad and motor vehicle transportation led to bigger, better, and longer tunnels. Today, not even mountains and oceans stand in the way. With the latest tunnel construction technology, engineers can bore through mountains, under rivers, and beneath bustling cities. Before carving a tunnel, engineers investigate ground conditions by analyzing soil and rock samples and drilling test holes.

Shotcrete is a liquid concrete that is sprayed on surfaces. Invented in 1907, it has been used as both a preliminary and a final lining for tunnels since the 1920s.

In 1931, the first drilling jumbos were devised to dig tunnels. These jumbos consisted of 24-30 pneumatic drills mounted on a frame welded to the bed of a truck. Modern jumbos allow a single operator to control several drills mounted on hydraulically controlled arms.

Raw Materials. Materials used in tunnels vary with the design and construction methods chosen for each project. Grout used to stabilize soil or fill voids behind the tunnel lining may contain various materials, including sodium silicate, lime, silica fume, cement, and bentonite (a highly absorbent volcanic clay). Bentonite-and-water slurry is also used as a suspension and transportation medium for muck (debris excavated from the tunnel) and as a lubricant for objects being pushed through the tunnel. Water is used to control dust during drilling and after blasting, which is often done with a low-freezing gelatine explosive. The most common modern lining material, concrete reinforced by either steel or fiber, may be sprayed on, cast in place, or prefabricated in panels.

Choice of method. A tunnel's construction method is determined by several factors, including geology, cost, and potential disruption of other activities. Different methods may be used on individual tunnels that are part of the same larger project; for example, four separate methods are being used on portions of Boston's Central Artery/Tunnel project.

The Manufacturing Process.

Preparing

• 1) Site geology is evaluated by examining surface features and subsurface core samples. A pilot tunnel about one-third the diameter of the planned main tunnel may be constructed along the entire route to further evaluate the geology and to test the selected construction method. The pilot tunnel may run alongside the main tunnel's path and eventually be connected to it at intervals to provide ventilation, service access, and an escape route. Or the pilot tunnel may be enlarged to produce the main tunnel.

• 2) If soil stabilization is required, it may be done by injecting grout through small pipes placed in the ground at intervals. Alternatively, a refrigerant may be circulated through pipes embedded in the ground to freeze the soil.

Mining

• 3) There are seven different methods used to remove material from the tunnel path.

T he first is the immersed tube method. Workers prepare an underwater tunnel site by digging a trench at the bottom of the waterway. Steel or reinforced concrete sections of tunnel shell are constructed on dry land. Each section may be several hundred feet (100 m or more) long. The ends of the section are sealed, and the section is floated to the tunnel site. The section is tied to anchors adjacent to the trench, and ballast tanks built into the section are flooded. As the section sinks, it is guided into place in the trench. The section is connected to the adjoining, previously placed section, and the plates sealing that end of each section are removed. A rubber seal between the two sections ensures a watertight connection.

In the cut-and-cover method workers dig a trench large enough to contain the tunnel and its shell. A box-shaped tube is constructed, often by in-place casting of reinforced concrete. In certain types of soil or in close proximity to other structures, tunnel walls may be built before digging begins in order to keep the trench from collapsing during excavation. When the tunnel shell has been completed, it is covered by replacing excavated soil.

The third method is the top-down method. A parallel pair of walls are embedded into the ground along the tunnel's route by driving steel sheet piles or constructing slurry walls. A trench is dug between the walls to a depth equal to the planned distance from the surface to the inside of the tunnel roof. The tunnel roof is formed between the walls by framing and pouring reinforced concrete on the bottom of the shallow trench. After the tunnel roof has cured, it is covered with a waterproofing membrane and excavated soil is replaced above it.

Shield tunneling. This "shotcrete" lining may be supplemented by inserting long steel rods (rock bolts) into the rock and tightening nuts against steel plates surrounding the head of each bolt.

A fifth method to remove material from the tunnel is the shield driving or tunnel jacking method. Some tunnels are still dug using a Greathead-style shield. The top of the shield extends beyond the sides and bottom, providing a protective roof for workers digging in advance of the shield. Excavation may be done by hand or with power tools. Excess material is passed back through the shield on a convey or belt, loaded into carts, and hauled out of the tunnel. After the shield has moved forward, the jacks are retracted, and steel or reinforced concrete ring segments are bolted into place to form a section of permanent lining for the tunnel.

T unnel jacking is a similar technique, but the shield being driven through the ground is actually a prefabricated section of tunnel lining.

The final method is the tunnel boring machine method. The types and arrangement of cutting devices on the face of the TBM are determined by the geology at the tunnel site. The face slowly rotates and grinds away the rock and soil in front of it. Bentonite may be pumped through the TBM face to make the soil surface more workable and to carry away the muck.

Final lining

• 4) In some cases, the final lining is placed during the excavation process. Two examples are TBMs that install lining segments and prefabricated tunnels that are jacked into place. In other cases, a final lining must be constructed after the entire tunnel is excavated.

There are three steps to a tunnel's success.

Today, engineers know that there are three basic steps to building a stable tunnel.

• The first step is excavation: engineers dig through the earth with a reliable tool or technique.

• The second step is support: engineers must support any unstable ground around them while they dig.

• The final step is lining: engineers add the final touches, like the roadway and lights, when the tunnel is structurally sound.