Unit 7 Types of Tunnels

1. Introduction

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	How many types of tunnels do you know?
2	What are the main kinds of mining?
3	What were the earliest tunnels used for?
4	Where do water tunnels deliver water to?
5	When was one of the first roadway tunnels constructed?
6	What do motor-traffic tunnels provide?
7	What is the method of tunnel construction depend on?

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	ground conditions		9	an artificial waterway
2	shallow trench		10	to house
3	mine tunnel		11	a motor traffic tunnel
4	hard rock		12	soft clay
5	to withstand		13	a traffic jam
6	to be bounded by…		14	open-throat section
7	underground chamber		15	vehicles
8	approximately		16	to dedicate

There are three broad categories of tunnels: mining (mine), public works ( eg. water tunnels) and transportation (eg. railroad tunnels, motor-traffic tunnels).

M ine tunnels are used during ore extraction, enabling laborers or equipment to access mineral and metal deposits deep inside the earth. These tunnels are made using similar techniques as other types of tunnels, but they cost less to build. Mine tunnels are not as safe as tunnels designed for permanent occupation, however.

Mine tunnels are made by blasting or by tunneling machines. Mine shafts are not usually lined, but they may have supports.

There are two basic kinds of mining, surface and underground. When you say 'tunnel' mining you're talking about underground mining.

Mining is driven by economics. It is much cheaper to dig an open pit mine. But, if the ore body is located deep enough that the waste rock on top can't be removed cheaply, then shafts or tunnels are dug to get to it. The depths can be extreme. In South African gold mines they are down to depths of nine miles.

Underground mines are used to exploit any kind of resource that happens to be found at that depth: coal, lead, gold, diamonds, etc.

P ublic works tunnels carry water, sewage or gas lines across great distances. The earliest tunnels were used to transport water to, and sewage away from, heavily populated regions. Roman engineers used an extensive network of tunnels to help carry water from mountain springs to cities and villages. These tunnels were part of aqueduct systems, which also comprised underground chambers and sloping bridge-like structures supported by a series of arches. By A.D. 97, nine aqueducts carried approximately 85 million gallons of water a day from mountain springs to the city of Rome.

T he great and highly advanced Roman waterway system known as the Aqueducts, are among the greatest achievements in the ancient world.

The aqueducts were built from a combination of stone, brick and the special volcanic cement pozzuolana.

Aqueducts, being the most visible and glorious piece of the ancient water system, stand as a testament to Roman engineering. Some of these ancient structures are still in use today in various capacities.

Water tunnels . Many tunnels provide water to city waterworks, to hydroelectric power plants, or to farms for irrigation. Others carry storm drainage or sewage. Most water tunnels measure 10 to 20 feet (3 to 6 meters) or more in diameter, and they have smooth linings that help the water flow. Many tunnels carrying water to hydroelectric power plants are lined with steel to withstand extremely high water pressures.

A water tunnel is an experimental facility used for testing the hydrodynamic behavior of submerged bodies in flowing water.

A hydrodynamic facility used for research, test, and evaluation, comprising a well-guided and

controlled stream of water in which items for test are placed.

Types of water-tunnel test sections with typical models. (a) Closed throat. (b) Open throat. (c) Free jet. (d) Free surface.

W ater tunnels may be classified, in part, by the type of test section used. The most common section is the closed throat (illus. a) in which the test section flow has solid boundaries. The advantage of this arrangement is its simplicity and efficiency, but the model must be small relative to the tunnel cross section to avoid large wall effects. Small wall effects are theoretically correctable. In an open-throat test section (illus. b) the water jet passes through a water-filled chamber of larger diameter. This minimizes wall effects, and many tunnels dedicated to propeller testing use such an arrangement.

When very low test section cavitation numbers are required, or for fully cavitating flows, a free jet (illus. c) in which the water jet passes through an air-filled chamber is useful. However, capture of the free jet and removal of excess entrained air prior to recirculation is not easily achieved over a broad range of test conditions. To study cavity flows on surface-piercing components or hydrofoils which operate near a free surface, a free-surface tunnel (illus. d) is required in which three sides of the water flow are bounded by solid walls and the upper surface is open to air at controlled pressure levels. This arrangement is often referred to as a water channel.

Water tunnels are used to investigate the dynamics, hydrodynamics, and cavitation of submerged and semisubmerged bodies such as propellers, ships, submarines, torpedoes, and hydrofoils and of turbomachinery. They are also indispensable to research on general flow phenomena in liquids.

Before there were trains and cars, there were transportation tunnels such as canals -- artificial waterways used for travel, shipping or irrigation. Just like railways and roadways today, canals usually ran above ground, but many required tunnels to pass efficiently through an obstacle, such as a mountain. Canal construction inspired some of the world's earliest tunnels.

The Underground Canal, located in Lancashire County and Manchester, England, was constructed from the mid- to late-1700s and includes miles of tunnels to house the underground canals.

By the 20th century, trains and cars had replaced canals as the primary form of transportation, leading to the construction of bigger, longer tunnels. The Holland Tunnel, completed in 1927, was one of the first roadway tunnels and is still one of the world's greatest engineering projects. Named for the engineer who oversaw construction, the tunnel ushers nearly 100,000 vehicles daily between New York City and New Jersey.

Railroad tunnels. Among the world’s greatest engineering feats was the boring of long railroad tunnels through the rocks of the Alps and the Rocky Mountains. Railroad tunnels reduce travelling time and increase the efficiency of trains.

M otor-traffic tunnels provide routes for automobiles, trucks, and other motor vehicles. Such tunnels have special equipment to remove exhaust fumes. For example, the Holland Tunnel , which is situated under the Hudson River and which links New York City and New Jersey, uses electric fans for ventilation. These fans are capable of completely changing the air in the tunnel every 90 seconds. Many motor-traffic tunnels also have signal lights and special monitoring systems to help prevent traffic jams.

Construction. 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.

There are three basic types of tunnel construction in common use:

• Cut and cover tunnels, constructed in a shallow trench and then covered over.

• Bored tunnels, constructed in situ, without removing the ground above. They are usually of circular or horseshoe cross-section.

• Immersed tube tunnels, sunk into a body of water and sit on, or are buried just under, its bed.

Building tunnels is a peak of the construction art and science. Walking or going through a tunnel is a very impressive thing for many people, nevertheless they don’t think about that at the instant.

Fact is that building tunnels is not necessary a modern knowledge. Unbelievable, but true, there are manmade tunnels which are very old. Very old, but not obsolete: an Iranian aqua duct serving for water transport is 5000 years old, and still in use! You don’t need to be a construction engineer for thinking about the difficulties of building a tunnel.

In the good old times the tunnels had mainly defense purposes, they were secret passages. In the modern times, things changed dramatically, but a tunnel remains a masterpiece.