THE HISTORY OF TUNNELING

It is probable that the first tunneling was done by prehistoric people seeking to enlarge their caves. All major ancient civilizations developed tunneling methods. In Babylonia, tunnels were used extensively for irrigation; and a brick-lined pedestrian passage some 3,000 feet (900 metres) long was built about 2180 to 2160 bc under the Euphrates River to connect the royal palace with the temple. Construction was accomplished by diverting the river during the dry season. The Egyptians developed techniques for cutting soft rocks with copper saws and hollow reed drills, both surrounded by an abrasive, a technique probably used first for quarrying stone blocks and later in excavating temple rooms inside rock cliffs. Even more elaborate temples were later excavated within solid rock in Ethiopia and India.

The Greeks and Romans both made extensive use of tunnels: to reclaim marshes by drainage and for water aqueducts, such as the 6th-century-BC Greek water tunnel on the isle of Samos driven some 3,400 feet through lime-largest stone with a cross section about 6 feet square. By that time surveying methods (commonly by string line and plumb bobs) had been introduced, and tunnels were advanced from a succession of closely spaced shafts to provide ventilation. Ventilation methods were primitive, often limited to waving a canvas at the mouth of the shaft, and most tunnels claimed the lives of hundreds or even thousands of the slaves used as workers.

Because the limited tunneling in the Middle Ages was principally for mining and military engineering, the next major advance was to meet Europe's growing transportation needs in the 17th century. The first of many major canal tunnels was the Canal du Midi (also known as Languedoc) tunnel in France, built in 1666-81 by Pierre Riquet as part of the first canal linking the Atlantic and the Mediterranean.

A notable canal tunnel in England was the Bridgewater Canal Tunnel, built in 1761 by James Brindley to carry coal to Manchester from the Worsley mine. Many more canal tunnels were dug in Europe and North America in the 18th and early 19th centuries. Though the canals fell into disuse with the introduction of railroads about 1830, the new form of transport produced a huge increase in tunneling, which continued for nearly 100 years as railroads expanded over the world.

Much pioneer railroad tunneling developed in England. A 3.5-mile tunnel (the Woodhead) of the Manchester-Sheffield Railroad (1839-45) was driven from five shafts up to 600 feet deep.

The great civil engineers of the nineteenth century were drawn into really grand tunneling. Two new kinds of transport created a need for tunnels. Railways had to lie on almost flat ground, and so did England's huge canal system. By the early 1800s those canals had become England's primary commercial trade network. Canals and railways, like the Roman aqueducts before them, spawned heroic tunneling through obstacles. Tunneling under rivers was considered impossible until the protective shield was de­veloped in England by Marc Brunei, a French emigre engineer. The first use of the shield, by Brunei and his son Isambard, was in 1825 on the Wapping-Rotherhithe Tunnel through clay under the Thames River. The tunnel was of horseshoe section 22'/4 by 37'/2 feet and brick-lined. After several floodings from hitting sand pockets and a seven-year shutdown for refinancing and building a second shield, the Brunels succeeded in completing the world's first true subaqueous tunnel in 1841, essentially nine years' work for a 1,200-foot-long tunnel. During the 19th and 20th centuries, the development of railroad and motor vehicle transportation led to bigger, better, and longer tunnels. With the latest tunnel construction technology, engineers can bore through mountains, under rivers, and beneath bustling cities. Before carving a tunnel, engineers investigate ground conditions by analyzing soil and rock samples and drilling test holes. Today, engineers know that there are three basic steps to building a stable tunnel. The first step is excavation: engineers dig through the earth with a reliable tool or technique. The second step is support: engineers must support any unstable ground around them while they dig. The final step is lining: engineers add the final touches, like the roadway and lights, when the tunnel is structurally sound. Worldwide efforts are under way to accelerate improvements in the technology of underground construction and are likely to be stimulated as a result of the 1970 OECD International Conference recommending improvement as government policy. The endeavour involves specialists such as geologists, soil- and rock-mechanics engineers, public-works designers, mining engineers, contractors, equipment and materials manufacturers, planners, and also lawyers, who aid in the search for more equitable contractual methods to share the risks of unknown geology and resulting extra costs.

Text . SUBWAY

Subway, also called underground, tube, or metro, underground railway system used to transport large numbers of passengers within urban and suburban areas. Subways are usually built under city streets for ease of construction, but they may take shortcuts and sometimes must pass under rivers. Outlying sections of the system usually emerge above-ground, becoming conventional railways or elevated transit lines. Subway trains are usually made up of a number of cars operated on the multiple-unit system.

There are three types of subways. One is called the open cut. The construction crew tears out the streets and builds the subways in deep ditches. If two lines are going to cross, the crew digs one roadbed deeper than the other. If the crew lays a pavement or other type of cover over the cut in the ground, the subway is called a cut and cover subway. The third form of subway, which is called a tube, is constructed by boring through the earth at the desired depth without disturbing the surface. This type of construction is for one or two tracks. The tunnels of an open-cut subway have a rectangular shape. The tunnels of a tube subway are usually circular or semicircular. New York City's subway is mainly rectangular. Much of the London subway is semicircular.

London's underground. The first subway system was proposed for London by Charles Pearson, a city solicitor, as part of a city-improvement plan shortly after the opening of the Thames Tunnel in 1843.

After 10 years of discussion, Parliament authorized the construction of 3.75 miles (6km) of underground railway between Farringdon Street and Bishop's Road, Paddington. Work on the Metropolitan Railway began in 1860 by cut-and-cover methods—that is, by making trenches along the streets, giving them brick sides, providing girders or a brick arch for the roof, and then restoring the roadway on top. On Jan. 10, 1863, the line was opened using steam locomotives that burned coke and, later, coal; despite sulfurous fumes, the line was a success from its opening, carrying 9,500,000 passengers in the first year of its existence. In 1866 the City of London and Southwark Subway Company (later the City and South London Railway) began work on their "tube" line, using a tunneling shield developed by J.I I. Greathead. The tunnels were driven at a depth sufficient to avoid interference with building foundations or public-utility works, and there was no disruption of street traffic. The original plan called for cable operation, but electric traction was substituted before the line was opened. Operation began on this first electric underground railway in 1890 with a uniform fare of two pence for any journey on the 3-mile (5-kilometre) line. In 1900 Charles Tyson Yerkes, an American railway magnate, arrived in London, and he was subsequently responsible for the construction of more tube railways arid for the electrification of the cut-and-cover lines. During World Wars I and II the tube stations performed the unplanned function of air-raid shelters. Today, London has 10 lines that provide quick, cheap transportation to all parts of the city and suburbs. This subway system is often called the tube or the underground. Some of its subway lines are so far underground that passengers go down on elevators. There are numerous escalators which help to keep the traffic moving. The first was installed in 1911. One of them at Leicester Square is over 80 feet in length. On long escalators the speed is changeable. The "up" escalator runs at full speed when carrying passengers, but when empty it runs at half speed. Many of the new escalators have automatic control making a more frequent service throughout the day possible.

Automatic trains, designed, built, and operated using aerospace and computer technology, have been developed in a few metropolitan areas, including a section of the London subway system, the Victoria Line (completed 1971). The first rapid-transit system to be designed for completely automatic operation is BART (Bay Area Rapid Transit). Air-conditioned trains with lightweight aluminum cars, smoother and faster rides due to refinements in track construction and car-support systems, and attention to the architectural appearance of and passenger safety in underground stations are other features of modern subway construction.