19.7 Answer the following questions

1. What are the main challengers in tunnel construction?

2. What geologic characteristics can influence the choice of driving methods?

3. What methods can minimize the risk of toppling in the tunnel heading?

4. Why is shield tunneling more efficient as compared to other technologies?

5. What are the advantages of the shield versus drill and blast tunnelling?

6. What are the advantages of full face tunnelling versus heading/bench excavation?

7. What are the main parts of a shield and what are their functions?

8. What are the main parts of the EPB type shield machine? Describe the technological process of this TBM.

9. What are the main parts of the SS type shield machine? Describe the technological process of this TBM.

10. Do the open-type machines erect concrete segment lining?

11. Why are the completed tunnels smaller in diameter than TBM’s?

12. What shield tunneling disadvantages define engineering imagination today?

13. Where does the shield personnel assemble small shields?

Unit 20 general idea of the metro

20.1 Read the text and find out peculiarities in the underground railway systems of different countries

The metro is a version of rapid transport of people comprising different modes of public transport like light metro, monorails and people movers (fig.20.1). In some cities in Germany, Austria, Switzerland and Denmark passengers travel by the fast metro-like railway line known as S-trains or S-Bahn which is a hybrid exhibiting features of both commuter rail systems and rapid transit.

a - Monorail	b - Elevated Metro Line
c - the S-trains can travel by usual railway tracks	d – People Mover (Moving Sidewalk) Перевозка людей на короткие расстояния

Figure 20.1 Rapid Transport Systems

The metropolitan known as subway or underground is the electric underground railway system with frequent station stops for fast transportation of large numbers of passengers in large cities. The metro runs through underground tunnels but it also may be elevated above street level on trestle bridges (fig.20.1b). For instance, the S-Bahn uses either underground or elevated tracks within the city centre, and can travel by usual railway tracks to suburbs and nearby towns.

Currently nearly 160 metropolitan areas all over the world have a metro system. The underground system in our country extends only within the city limits but in many foreign cities, it reaches outer suburbs by commuter rail networks. A synchronized timetable, electric locomotives and train doors at platform level allow the trains to use the railway lines (fig.20.1c).

The metro all over the world uses different types of line arrangement and may consist of one or several lines. Sometimes, lines can share tracks with each other. Some foreign metros use grade-crossing lines (fig. 20.2d), and each line has individual names, colours or numbering. For instance, the Paris Metro has a unique structure, arranged as crisscrossing lines with very densely spaced stations in the city core. The Prague Metro also has numerous interchange stations in the city central area. The Copenhagen Metro provides a high service frequency in the central city areas, and running through the city streets, it forks into suburb branches. The London Tube and the Moscow Metro are far-reaching underground rail systems with loop lines that connect the outward metro lines. Some underground railway systems share their central terminals with the city central railway station.

The metro lines in Russia are laid in different levels providing a safe service without any risks for train collisions. It is an effective way to travel within the city because buses, trolleybuses and tram routes or even commuter rail network run near metro stations. By traveling with underground system, passengers can get to their stop without changing trains or transfer between lines at interchange stations using connecting subways. Transit maps or schematic diagrams at stations and in cars show the line routes and stations. The lines are colour coded and the stations have their named icons. Regular audio announcements about the arriving trains also help passengers along with visual platform displays, boards and direction signs on the station walls. In Hong Kong the MTR passenger railway system provides bilingual real-time information on every platform.

Figure 20.2 Diagram of the Metro Lines (схема линий метро)

a – Underground Lines (подземные линии); b – Ground-level Lines (наземные линии); c – Elevated Lines (надземные линии);

d – Underground Lines crossed at the same level (пересечение линий в одном уровне);

e – Underground Lines crossed at didderent levels (пересечение линий в разных уровнях).

1 – Underground Lines (линии метрополитена);

2 – Underground Passage (подземный переход)

The advantages of the metro are its high speed, shorter headway and higher capacity in transporting large numbers of passengers. In addition to other beneficial effects, the metro settles the problems of traffic jams, air pollution and noise. The London Underground, opened in 1863, clearly demonstrated these advantages. The idea spread all over the world and not only to other European cities but to the United States and Asia, especially to China. The rapid growth of traffic flow in modern cities has given rise to the swift expansion of the metro because the drivers and passengers, who daily waste their time in traffic congestion and lose their health and even lives in daily traffic accidents, want safer, faster and top-quality services. The expected growth of chronic hold-ups and bottlenecks in city streets, continual and sharp increase in fuel prices makes the owners of private cars travel by public transport, and mega-cities see the metro as a sustainable means of mobility. Currently many countries are developing their underground transit networks though their construction, within the city areas, is a rather complicated and expensive engineering work.

In our country, the metro differs from the railways by the track gauge, and the current collection devices. It provides its service on rails between stations using the power delivered either by a third rail or by overhead wires where the metro line is at ground level, for instance, at the terminal stations (fig.20.3d).

a – Subway train-set using rubber tires	b - Driver-free train-set at ground-level line (поезд  с автоматическим управлением на наземной линии метро)
c – Metro Street Facility (наземный вестибюль)	d – Depot (депо)

Figure 20.3 Metro Rolling Stock and Facilities

Metro trains are multiple units with three or more cars per train that can accommodate a large number of people (fig. 20.3a,b). S-Bahn uses bi-level carriages that are more spacious and allow better seating areas for passengers. The transit capacity of metro lines depends on the service frequency, the number of passengers, accommodated in cars, and train-set length. The car capacity ranges from 90 to 270 passengers per car, and the ratio of seated to standing passengers may be varying. The MTR Corporation in Hong Kong attains its highest capacity of 80,000 people per hour. The headway is much shorter compared to other modes of public transit system and ranges from ninety seconds to six minutes.

The idea of the innovative underground railway system has been developing by a part of the London Rail division of Transport for London known as Dockland Light Railway. DRL involves several ground metro lines with the fully computerized signaling system. It operates the driver-free train-sets guaranteeing a safe distance between them. The sustem gives information about each train-set location, controls the fully automatic car doors and stops train-sets at stations. As there is no driver’s cab in the first car, the passengers use the front passenger seats immediately at the large and spotlessly clean car windshield (fig. 20.3b). However, the train-sets cannot manage entirely without 'drivers'. At certain stations, a uniformed Train Captain enters the car and, if required, takes manual control for the safe train travelling at difficult station spans. He or she also checks tickets and can give information or advice. Then the Train Captain leaves the car and the train returns to central computer-aided control. The platforms at all DLR stations have ramp or lift access. In case of experiencing any problems, the passengers can talk directly with a member of DLR staff as all lifts are equipped with enabled alarms. For easy access onto the trains, the open space between the train and the platform edge is no more than 7.5 cm. The steps from the platform to the train are 5cm in height. Passengers use standard travel tickets, monthly and seasonal tickets on these lines.

The Metro always provides stimulating competition to the surface transport system owing to its good service and safe, reliable and convenient passenger travel. Therefore, the metro is much more than a means of moving people around, it is also a prestige showcase in the face of the competition between cities.

Exercises