The history of bridge and tunnel building
1. An outstanding statesman once said in his speech, 'There can be little doubt that in many ways the story of bridge-building is the story of civilization. By it we can readily measure an important part of a people's progress." Great rivers are important means of communication, for in many parts of the world they have been, and still are, the chief roads. But they are also barriers to communication, and people have always been concerned with finding ways to cross them.
2. For hundreds of years men have built bridges over fast-flowing rivers or deep and rocky canyons. Early man probably got the idea of a bridge from a tree fallen across a stream. From this, at a later stage, a bridge on a very simple bracket or cantilever principle1 was evolved. Timber beams were embedded into the banks on each side of the river with their ends extending over the water. These made simple supports for a central beam reaching across from one bracket to the other. Bridges of this type are still used in Japan, and in India. A simple bridge on the suspension principle2 was made by early man by means of ropes, and is still used in countries such as Tibet. Two parallel ropes suspended from rocks or trees on each bank of the river, with a platform of woven mats laid across them, made a secure crossing. Further ropes as handrails3were added. When the Spaniards reached South America, they found that the Incas of Peru used suspension bridges made of six strong cables, four of which supported a platform and two served as rails.
3. All these bridges made possible crossings only over narrow rivers The type of temporary floating bridge,4 the pontoon bridge, has been used for military purposes; military engineers can construct a temporary bridge on this principle, able to carry all the heavy equipment of a modem army, in an extremely short time.
The idea of driving wooden piles into the bed of the river in order to support a platform was put into practice 3,500 years ago. This is the basis of the 'trestle' or pile bridge5 which makes it possible to build a wider crossing easier for the transport of animals and goods.
4.With the coming of the railway in the 19th century there was a great
demand for bridges, and the railways had capital for building them The first railway bridges were built of stone or brick. In many places long lines of viaducts were built to carry railways; for instance, there are miles of brick viaducts supporting railways to London.
The next important development in bridge-building was the use of iron and, later, steel. The first iron bridge crossed the river Severn in Great Britain.
The idea of a drawbridge,6 a bridge hinged so that it can be lifted by chains from inside to prevent passage, is an old one. Some St. Petersburg bridges were built on this principle.
A modern bridge probably demands greater skill from designer and builder than any other civil engineering project. Many things should be taken into consideration,, and these may vary widely according to local conditions. In deciding what type of bridge is most suitable the designer has to consider the type and weight of the traffic, and width and depth of the gap to be bridged, the nature of the foundations and the method of erecting the bridge. The designer has to calculate carefully how the various loads would be distributed and to decide which building materials are more suitable for carrying these loads.
Tunnels
5.Tunnelling is difficult, expensive and dangerous engineering work.
Tunnels are built to provide direct automobile or railway routes through
mountain ranges, under or over rivers. They can also provide underground
channels for water, sewage or oil. Before the 19th century men had not
acquired enough skill in engineering to carry out extensive tunnelling.
Tunnels, however, were known in ancient times. They were, for instance,
driven into the rock under the Pyramids of Egypt, and the Romans built one
in Rome for their chief drain, parts of which still remain. One of the earliest
tunnels known was made in Babylon. It passed under the Euphrates river,
and was built of arched brickwork being 12 feet high and 15 feet wide.
Other ancient tunnels were built for water supply and for drainage.
6.Modem tunnels are often very long and deep. The SimpIon Tunnel on
the France-to-Italy railway, for example, is 12 miles long and in one place
the peaks of the Alps rise over 6,000 feet above it. Some tunnels are over 50
feet in diameter. Many are circular in cross-section. Others are horseshoe-
shaped,7 with a level floor on which it is easy to lay permanent roads and
railways.
Tunnel Under Channel.
7.Connecting the Isles of Great Britain to mainland Europe is a fantasy
that can be dated back nearly 200 years.
We can name very few projects against which there existed a deeper and more powerful prejudice than the construction of a railway tunnel between Dover and Calais.
The objections have been cultural, political and, of course, military. The British government objected to the scheme mainly because they thought that the enemy could easily invade England through such a tunnel.
The first suggestion to construct a tunnel came from Napoleon in 1800. His engineers even drafted a tunnel plan, but Britain and France were at war at that time.
In 1988 the question of a Channel Tunnel was studied afresh by a group of French and British engineers and the work actually began. They agreed to start boring for the Eurotunnel on both English and French Coasts.
The Tunnel runs under the sea through a layer of dense chalk which is known to be free of cracks and allows water to penetrate it slowly.
The work proceeded very quickly and was successfully completed in about six years. The Tunnel was opened to traffic on May 7, 1994.
Two main tunnels, with service tunnel between, carry one-way rail traffic.
8.Original estimate was 7.2 billion dollars at current exchange rates, but cost to date is 13.1 billion dollars shared between Britain, France and other investors. So far the project is not quite profitable and still needs more
investments.
Cars and trucks carried by rail make the crossing in 35 minutes, about an hour less than by ferry. Passengers remain in their vehicles.
The Tunnel personnel does its best to make passengers feel comfortable and safe during the crossing. But as it was mentioned by the commercial director of the Tunnel, they still have many serious problems and one of them is security. Nevertheless, the authorities are sure to be able to solve all the problems successfully.
Notes:
1 a bridge on a bracket or cantilever principle (= a bracket or cantilever bridge) -консольный мост
2 a bridge on the suspension principle (suspension bridge) - висячий
(подвесной) мост
3 handrails - поручни
4 a floating bridge - понтонный мост
5 a “trestle” or pile bridge — мост на рамных основах
6 a drawbridge - разводной мост
7 horseshoe-shaped - подковообразный
ВАРИАНТ№ 2
The Triumph OF HUMAN SPIRIT
The Brooklyn Bridge was built in the year 1883. It is still one of the
most popular places of interest in New York.
The plan for the Brooklyn Bridge was made by a man named John Roebling. This was in the year 1867.
Roebling was a German. He emigrated to the United States when he was twenty-five. In 1867 Roebling was already quite famous. Years before he had invented the steel cable (трос). Using this steel cable he built several bridges, one at Niagara Falls (Ниагарский водопад) and a second across the Monogahela River at Pittsburgh. He was sure he could build this new bridge.
It was decided to give Roebling a chance. A company was organized. Roebling was head engineer. He began to work making the plans for the bridge. He sent his son Washington to Europe to study some new bridges there. Some experiments had been made with working in a large box under water.
And then the accident happened. Roebling was working near the river. A boat struck the dock on which he was standing. Two weeks later he died. Before he died he asked that his son Washington should continue his work.
W. Roebling began to work with the same interest and energy as his father. The bridge was begun. There were many problems. According to the plans, there were to be two large towers (башни). One of these towers was to be on the Brooklyn side of the river and the other was to be on the I Manhattan side. From the towers hung (свешиваться) a system of steel cables. These steel cables were to hold (удерживать) the bridge.
Today engineers know how to do these things. They have had experience. They have special machines. But at that time no one knew exactly how to do this work. The Brooklyn Bridge was the first bridge of its kind in the world. They used the new box that Washington Roebling had studied in Europe. The box was made of wood and was about the size of a house. In this box men could work under water. Air was forced into the box and the water was forced out of it. It was very dangerous. No one understood the problems of this kind of work. Men became sick. There were many accidents. Roebling himself worked with the men in the box. He tried to encourage the men.
One day a worker went down into the box. He felt perfectly well. Within half an hour he began to feel strong pains (боль). Five minutes later he was dead. The same thing happened to other men. One day Roebling himself had a similar attack. He could not talk. He could not hear. He became paralysed. After a week or two he felt better. He went back again to work in the box. He had a second attack, more serious than the first. He could not work again. In feet he was unable to work again during the rest of his life. He remained a cripple (калека). Yet the work had to continue. And Washington Roebling continued to direct the construction of the bridge. His home was near the bridge. He used a telescope. He watched the work every day. His wife helped him. Each day she went to the bridge. She carried her husband's orders to the men. She worked with the men. At night she returned to her husband. She told him about the work of the day. In this way, year after year, the work continued.
In 1876 the first cable was placed from one tower to the other. In 1883 about fifteen years after it was first begun, the bridge was officially opened. Many important people, including the President of the US, took part in the ceremony. Washington Roebling watched the ceremony through his telescope.
The bridge was one of the wonders of the nineteenth century. It is still today. There is more traffic on it today than ever before. The bridge remains very strong. It also remains a monument to the two men who built it, John Roebling and his son Washington.
LONDON AS A PORT
1. What are the "hands" of London known for?
The port of London is to the east of the City. Here, today, are miles and miles of docks, and the great industrial areas that depend upon shipping. This is the East End of London, unattractive (непривлекательный) in appearance, but very important to the country's commerce. The East End is a great proletarian area populated by factory workers, and small craftsmen. The East End is the "hands" of London. The hands which have built the palaces, theatres, shops and hotels, the hands which unload the cargoes in the docks, which make furniture (мебель), dresses, motor cars, and a million and one other things which fill the shops.
2. How were the goods unloaded in the early days?
The River Thames, flowing from west to east, divides London into two parts known as the north bank and the south bank. Years ago the Thames used to overflow its banks when the tide (прилив) came up, but now it has been banked up and you see a fine wide roadway called the Embankment. The Thames estuary (устье) offered excellent facilities for shipping. The deep channel and high tide of the lower river enable vessels to pass inland as far as the bridge and unload in waters that were little troubled by heavy storms in the North Sea. In the early days they anchored (бросать якорь) in the river and unloaded into small boats and barges which carried the goods to landing-places on the banks.
3. How are the goods unloaded now?
As the ships grew larger this became too slow a process, and the river was overcrowded, so docks were constructed, deep-water basins excavated in the banks of the river, where vessels could come alongside and unloaded their cargoes directly on the wharves (пристань) or even into lorries if necessary. Vessels increased rapidly in size during the last century and are still growing, and hence, larger and larger docks have had to be constructed with deeper and deeper basins.
4. When can ocean-going ships go up the Thames?
The Thames has the benefit (преимущество) of a good tidal range so that the biggest vessels can go up the river and enter docks at high tide. By closing the dock gates and thus shutting off their waters from the river, deep water can be maintained in the dock all the time it is occupied by vessels. On the river there are ocean-going ships, and lines of barges pulled along by tugs (буксир). Ships up to 6,000 tons can come as far as London Bridge below which is the part of the river called the Pool.
5. How are the two halves of the drawbridge raised?
The ships can pass under Tower Bridge. It was designed by Sir Horace Jones, London architect, and Sir John Wolfe Barry, civil engineer. It took eight years to build it (1886-1894). It has permanent spans (пролет) 270 feet long, suspended on great chains, connecting them with the river bank and smaller towers (башня) at the shore approaches. The two halves of the drawbridge each weighing 100 tons, can be raised for the passage of ships by hydraulic machinery in a minute and a half only.
ВАРИАНТ №3