2383

THE UNDERGROUND RAILWAY SYSTEM STRUCTURES

The track construction of the Underground Railway System differs from the usual railway track. The sleepers of the railroad track rest upon a bed of crushed rock or gravel, which is called ballast. The tracks of the underground railway are laid directly on concrete base. The main idea of using concrete in this case is to keep air free from dust but it involves heavy outlays. Were the track imbedded in foundation materials i.e. slag, gravel, ash, sand, hard earth or even broken stone, the trains would be followed by the dust clouds.

The ties or sleepers in the metro are shorter than those of the railroad track, which are 2,7m long. The metro sleepers are only 0,9 m long. They are separated by a chute. The contact rail is laid along the whole track and arranged to carry high voltage current of 825 volts. It is attached to the brackets and transmits the direct current to the train electromotor through the pantograph.

The underground railway subsurface and oversurface structures involve stations, main line tunnels, lobbies, tunnels for moving stairways and escalators, underpasses, ventilation and sanitary engineering as well as a power supply system.

The main unit of any underground railway system is a main line or running tunnel. All running tunnels may be subdivided into single-lane one-way tunnels, double-lane and four-lane tunnels. The New York Underground has two usual lanes and two high-speed lanes called «expressway». The lining in main line tunnels is of circular shape. As a rule, it is erected of the reinforced concrete segments or cast iron liners, i.e. it is assembled from separate units. Crossover tracks can divert the trains from one track to another. The trains may be inspected and repaired at the dead-ends.

Needless to say the stations represent one of the main parts of the underground railway system to provide the wide choice of services for passengers. Attractively designed underground structures represent a continuation of the above-ground architecture. The stream of passengers can move freely through entrances and exits of the aboveground and underground lobbies using special staircases linking the underground areas with the over surface streets. After a while, passengers no longer notice whether they are moving above or below ground because the structural layout itself as well as the different functions offered within the space, extend the main «room of action» and also create the atmosphere of «city within the city». Underground stations are regarded as most efficient because they provide the spacious lobbies and leave the city areas for other public needs. One underground station may have up to nine entrances and exits. The height difference inside the underground lobbies is almost completely canceled out by the structural arrangements. The width of some underground passages ranges between two and six meters, their height cannot be less than 2,5 m. The passengers can move from one station concourse to another or from one entrance – exit lobby to another one walking along these underpasses. In

addition, escalators and stairways are provided to allow passengers to change levels.

An escalation complex involves an inclined stairways tunnel for the three stairways within it, a power-driven station to move the staircases and a pull chamber. As a rule, this tunnel’s diameter is 8,1m. The escalators of Russian production provide the lifting of the passengers up to 65 m.

IV. Match the English and the Russian equivalents. Use the English words in the sentences of your own.

V. Mark these sentences true, false or not given.

1._______ There is no difference between the usual railway and underground railway tracks.

2._______ When the underground railway tracks are imbedded in ash, the trains are followed by the dust clouds.

3._______ The sleepers of the railroad track are separated by a chute.

4._______ The dimensions of the metro station are influenced by the number of passengers to be carried.

5._______ Any underground railway system can easily work without a running tunnel.

6._______ An escalation complex consists of a stairways tunnel, a powerdriven station and a pull chamber.

VI. Restore the text (guess the words under the blots) and retell it to your partner.

The underground stations may be of different structural layout. There are offboarding platforms and boarding platforms.

Platforms are very important parts of the station concourses because they accommodate passengers and allow them enter, leave and change the trains. To determine the optimum capacity of an underground station it is necessary to consider the busy rate i.e. number of passengers carried through this station.

The main quantity index of any station is rated within the following limits:

-the quantity of passengers for an ordinary station must be equal to 20 – 30 % of a total train capacity;

-the quantity of passengers for the stations located near terminals, theaters etc.

up the tunnel height and width.

The third problem is caused by the tunnel lining in case it is erected in the seismically active areas. The lining is influenced by the Earth’s crust shift and other displacement processes occurring within a massif. Tunneling through various sorts of rock can result in different effects and conditions influencing the lining especially when the blasting technique, is employed. Permanent supervision and inspection is set up for the lining elements in case of shifts in block joints or incipient cracks in concrete and iron cast segments. The tunnel supervisors use special screeds attached to the lining surface to watch the dynamics of the running processes.

Water discharging is considered to be another complicated problem turning to become most important one for the tunnels, which are driven under the severe climatic conditions. For instance, the railway tunnels along Abakan-Taishet mainline in Siberia can suffer from the ice crust in gutters in winter when the water freezes and binders or even blocks train running.

The gutters are built at both sides of the railway track for water discharging. The water entering the tunnel is calculated and rated value influences the dimensions of the gutters and their lengthwise grade. The gutters appear to be a vital element in tunnel operation and call for extra maintenance cost under low temperatures because they need heating or special encasement for warmthkeeping.

There are some more problems facing the tunnels and above all ventilation and lightning should be taken into consideration.

Ventilation is among the most complicated problems which vehicular tunnels face under operation. Ventilation facilities are essential because the underground road is a motor way within a tunnel structure. Air contamination calls for various types of ventilation facilities due to toxic auto emissions. Tunnel design takes full account of all the possibilities to provide a sound layout of the tunnel itself and efficient arrangement of ventilation facilities.

The simplest ventilation technique offers to arrange both ports at different levels providing natural ventilation due to the difference between air pressure at both ends.

One more idea of tunnel design may be applied to the large-diameter short tunnels which can be oriented along the dominating direction of the winds providing adequate natural ventilation.

But the majority of the tunnels need artificial mechanical or forced ventilation and face the problem of estimation the volume of the air required. There is a special estimation technique taking into consideration the tunnel dimensions, the volume of traffic, etc. The general tunnel ventilation involves blowing, exhaust and combined ventilation. The blowing ventilation supplies fresh air from the unpolluted source – usually at the portal. The air is forced through a pipe and discharged at a place where it is needed. The foul air drifts

back to the portal. By the exhaust method, foul air is pulled out through the pipe and the fresh air enters at the portal. The combination of these methods uses the fans to draw out the dust and auto emissions and then the fan are reversed.

Many tunnels are designed with ventilation stations including the ventilation tower and machinery rooms equipped with fans, power receiving and transforming equipment, dust collectors, mufflers and ventilation control devices. Some tunnels are equipped with a lateral flow ventilation system. In this system the air taken in at the ventilation station is fed into the tunnel to dilute auto emissions. The air is discharged from the tunnel after the dust has been removed from it. The name of the system derives from the fact that the air for ventilation flows laterally in the motor way through the feeding and discharging ducts.

In a concentrated discharge system, diluted auto emissions are absorbed by force near the entrance of a tunnel and discharged after the dust is removed from them. This system controls the leakage of exhaust gas from the tunnel entrance.

Tunnel lightning is very important from the point of view of safety measures. If an accident occurs in a tunnel road in a city, it will have a major effect not only inside the tunnel, but also on urban activities on the surface because vehicles may carry hazardous loads. That is why special consideration is given to lightning at the design development phase. For instance, some tunnels in Switzerland are equipped with solar batteries which are used in remote areas in the mountains.

IV. Find 11 pairs of synonyms:

disastrous; poisonous; various; catastrophic; safe; necessary; escape; protected; happen; different; proportions; toxic; town; remove; essential; phase; dimensions; exhaust; occur; leak; urban; stage

V. What notion is explained by the following definition?

-equipment for providing light for a room, building, etc;

-to allow air to enter and move freely through a room, building, etc;

-a device with blades that are operated mechanically to create a current of cool air;

-to allow liquid or gas to get in or out wrongly;

-a device that fix something firmly;

-a thing that is difficult to deal with or understand

VI. Use the following phrases in the sentences of your own and let your partner translate them.

In charge of; needless to say; side by side; depend on; in addition; result in; due to; taking into consideration; from the point of view of.

VII. Complete the following sentences. Choose your answers from the box. There are more words than you will need.

1.Tunnel maintenance includes railway track maintenance, shipping clearances testing, water discharging, ventilation, lightning and … inspection.

2.The dynamics of the running processes in the seismically active areas are tested by…

3.… call for extra maintenance cost under low temperatures.

4.The majority of the tunnels need … ventilation.

5.… must be taken into consideration at the design development phase.

lining lightning forced screens screeds gutters forcing

VIII. Cross out the words/word combinations, which cannot be used in description of tunnel maintenance.

current, careful, difficult, expensive, negligible, necessary, labour-intensive, profitable, interesting

IX. Retell the text using Ex. II and the word combinations below.

1. The title of the story I want to tell you is… 2. First of all… 3. Second I would like to say that… 4. As far as I understand… 5. In fact… 6. As far as I remember… 7. In conclusion I’d like…

Home Exercises

I.Memorize the words from Ex. I page 145.

II. Change the Voice of the sentences where it is possible.

1.Tunnel supervisors gave special attention to the maintenance of the railway track.

2.They erected a tunnel in the seismically active area that’s why there are a lot of problems with it.

3.We are going to use the blasting technique.

4.The tunnel was closed because of the damaged ventilation.

5.They need much more money for gutters repairing.

the Earth’s crust result in vertical up to 7m and horizontal up to 4m displacements. In response to such displacements the spans can be thrown off the supports because the piers themselves can be damaged and to a great extent move into an inclined position or even displaced.

But it is worth noting that during the most reported quakes the constructional works have suffered not nearly so much as other civil-engineering works because of the mitigation of earthquake damage. The earthquake in Japan crushed 85 % of dwellings in Tokyo on September 1, 1923. But the bridge works could withstand the disaster and only 337 from a total number of 1028 bridges failed. 2 .

Hurricanes also cannot result in the bridge collapse because at present the building codes take into consideration the forces of the most violent winds and calculate them with great precision. In 1879 the bridge having five spans 75 m long was thrown off the piers on the lake Tay in Great Britain. The train moving along the bridge at the moment of a severe gust added an extra area for the impact of the wind the speed of which was about 140 kph. In 1904 the viaduct supports 90 m high were overthrown and the 76 m long bays fell down under the wind blowing at 280 kph in St. Paul City, U.S.

3 In 1938 the ice accretion or ice jam which was more than 27 m

thick and 120 m long cut the abutment of the arch span 256 m long on the Niagara River, U.S. The bridge had been in service for forty years and the ice

The ablation and scour of the support foundations resulted in the bridge collapse on the Uvod-river in Russia in 1881. The speed of the river current increased because of the channel constriction and leads to the 5 m deep hollow in the soft slimy ground.

The lack of the knowledge about the metal behavior led to the bridge collapse in Belgium in 1938. 5 This metal condition is called

brittleness or shortness of steel. It is caused by the high carbon content of steel.

AIce impact is also rather dangerous for the bridge works.

BNo place on earth may be safe from the possibility of tectonic mayhem.

CWhen the air temperature dropped abruptly to the low subzero points some of the metal elements of the arch span burst even without any additional loads.

DAnd in fact the Great Tashkent Еarthquake in 1966 did not break down or could seriously distract any constructional work.

EThe last ice jam was building up during 36 hours but nothing was done to blast it off.