III. Insert the words from the list

subway, cars, trench, lead, street traffic, overhead, masonry, cut-and-cover method, shafts

1. Many other cities followed London’s …. In Budapest, a 2.5 mile electric subway was opened in 1896, using single … with trolley poles; it was the first subway on the European continent. Considerable savings were achieved in its construction over earlier … using a flat roof with steel beams instead of a brick arch, and therefore a shallower …. In Paris the rapid progress was attributed to the wide streets … and the modification of the cut-and-cover method devised by the French engineer F.Bienvenue. Vertical … were sunk at intervals along the route; and from there side trenches were dug and … foundations to support wooden shuttering were placed immediately under the road surfaces. Construction of the roof arch then proceeded with relatively little disturbance to …. This method, while it is still used in Paris, has not been widely copied in … construction elsewhere.

IV. Fill in the gaps with suitable derivatives of the words given on the right:

In the United States the first … subway line was constructed in Boston between 1895 and 1897. It was 1.5 miles … and at first used trolley streetcars or tramcars. Later Boston acquired … subway trains. New York City opened the first section of what was to become the … system in the world on October 27, 1904. In Canada, Toronto opened a subway in 1954, a second system was constructed in Montreal during the 1960s … Paris-type rubber-tires cars. In Mexico City the first stage of a … underground and surface metro system was opened in 1969.

practice length convention large use combine

FOLLOW UP ACTIVITIES

Speak on: 1. Kinds of tunnels. 2. Minsk underground.

Unit 7: TUNNELING TECHNIQUES

Find the following terms and memorize their meanings

Submerged tunnel Jack

Jumbo Shale

Rock tunnel Sandstone

Muck Friable

Shield Access

Mucker Bed

Reversible

Text 1: BASIC TUNNELING SYSTEM

Tunnels are generally grouped in four broad categories, depending on the material through which they pass: soft ground, consisting of soil and very weak rock; hard rock; soft rock, such as shale, chalk, and friable sandstone; and subaqueous. While these four broad types of ground condition require very different methods of excavation and ground support, nevertheless, nearly all tunneling operations involve certain basic procedures: investigation, excavation and materials transport, ground support, and environmental control. Similarly, tunnels for mining and for civil-engineering projects share the basic procedures but differ greatly in the design approach toward permanence, owing to their differing purposes. Many mining tunnels have been planned only for minimum-cost temporary use during ore extraction, although the growing desire of surface owners for legal protection against subsequent tunnel collapse may cause this to change. By contrast, most civil-engineering or public-works tunnels involve continued human occupancy plus full protection of adjacent owners and are much more conservatively designed for permanent safety. In all tunnels, geologic conditions play the dominant role in governing the acceptability of construction methods and the practicality of different designs.

Geologic investigation. Thorough geologic analysis is essential in order to assess the relative risks of different locations and to reduce the uncertainties of ground and water conditions at the location chosen. In addition to soil and rock types, key factors include the initial defects controlling behaviour of the rock mass; size of rock block between joints; weak beds and zones, including faults, shear zones, and altered areas weakened by weathering or thermal action; groundwater, including flow pattern and pressure; plus several special hazards, such as heat, gas, and earthquake risk. For mountain regions the large cost and long time required for deep borings generally limit their number; but much can be learned from thorough aerial and surface surveys, plus well-logging and geophysical techniques developed in the oil industry.

Excavation and materials handling. Excavation of the ground within the tunnel bore may be either semicontinuous, as by handheld power tools or mining machine, or cyclic, as by drilling and blasting methods for harder rock. Here each cycle involves drilling, loading explosive, blasting, ventilating fumes, and excavation of the blasted rock (called mucking). Commonly, the mucker is a type of front-end loader that moves the broken rock onto a belt conveyor that dumps it into a hauling system of cars or trucks. As all operations are concentrated at the heading, congestion is chronic, and much ingenuity has gone into designing equipment able to work in a small space. Since progress depends on the rate of heading advance, it is often facilitated by mining several headings simultaneously, as opening up intermediate headings from shafts or from adits driven to provide extra points of access for longer tunnels.

For smaller diameters and longer tunnels, a narrow-gauge railroad is commonly employed to take out the muck and bring in workers and construction material. For larger-size bores of short to moderate length, trucks are generally preferred.

Ground support. The dominant factor in all phases of the tunneling system is the extent of support needed to hold the surrounding ground safely. Engineers must consider the type of support, its strength, and how soon it must be installed after excavation. The key factor in timing support installation is so-called stand-up time— i.e., how long the ground will safely stand by itself at the heading, thus providing a period for installing supports. In soft ground, stand-up time can vary from seconds in such soils as loose stand up-to hours in such ground as cohesive clay and even drops to zero in flowing ground below the water table, where inward seepage moves loose sand into the tunnel. Stand-up time in rock may vary from minutes in raveling ground (closely fractured rock where pieces gradually loosen and fall) up to days in moderately jointed rock (joint spacing in feet) and may even be measured in centuries in nearly intact rock, where the rock-block size (between joints) equals or exceeds size of the tunnel opening, thus requiring no support.

In early tunnels, timber was used for the initial or temporary support, followed by a permanent lining of brick or stone masonry. Since steel became available, it has been widely used as the first temporary stage or primary support. For protection against corrosion, it is nearly always encased in concrete as a second stage or final lining. Steel-rib support with timber blocking outside has been widely employed in rock tunnels.

Environmental control. In all but the shortest tunnels, control of the environment is essential to provide safe working conditions. Ventilation is vital, both to provide fresh air and to remove explosive gases such as methane and noxious gases, including blast fumes. While the problem is reduced by using diesel engines with exhaust scrubbers and by selecting only low-fume explosives for underground use, long tunnels involve a major ventilating plant that employs a forced draft through lightweight pipes up to three feet in diameter and with booster fans at intervals.

Electronic equipment in tunnels is prohibited, since stray currents may activate blasting circuits. Thunderstorms may also produce stray currents and require special precautions.

COMPREHENSION CHECK

I. Decide whether the following statements are true or false according to the text:

1. Tunnels are divided into four groups depending on the ground through which they pass.

2. All kinds of tunnels require the same methods of excavation and ground support.

3. Thorough geologic analysis is one of the main tunneling operations.

4. Excavation of the ground is either cyclic or continuous.

5. Each cycle involves drilling, loading explosive, blasting, ventilating fumes and excavation of the blasted rock.

6. The dominant factor in all phases of the tunneling system is ground support.

7. In soft ground stand-up time can vary from minutes up to hours.

8. In rock stand-up time may vary from seconds up to days.

9. Ventilation provides fresh air and removes explosive gases.

10. Electronic equipment is widely used in tunnels.

II. Answer the questions

1. How are tunnels generally grouped?

2. What do tunneling operations involve?

3. Why is thorough geologic analysis very important?

4. What does each cycle involve?

5. How long will soft ground safely stand by itself at the heading?

6. Stand-up time in rock varies from minutes up to days, doesn’t it?

7. Where is control of environment essential?

8. How does ventilation work?

9. What tunnels involve a major ventilating plant?

10. Why is electronic equipment prohibited in tunnels?

LANGUAGE FOCUS

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