Online Encyclopedia
Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.
TUNNEL (Fr. tonne!, later tonneau, a ...
Online EncyclopediaEncyclopedia Home :: TUM-VAN
del.icio.us it!
|
See also:TUNNEL (Fr. tonne!, later tonneau, a diminutive from See also:Low See also:Lat. tonna, tunna, a See also:tun, cask)
, a more or less See also:horizontal under-ground passage made without removing the See also:top See also:soil
.
In former times any See also:long See also:tube-like passage, however constructed, was called a See also:tunnel
.
At the See also:present See also:day the word is sometimes popularly applied to an underground passage constructed by trenching down from the See also:surface to build the arching and then refilling with the top soil; but a passage so constructed, although indistinguishable from a tunnel when completed, is more See also:cor-
rectly termed a " covered way," and the operations " cutting " and " covering," instead of tunnelling
.
Making a small tunnel, afterwards to be converted into a larger one, is called " See also:driving a heading," and in See also:mining operations small tunnels are termed " galleries," " driftways " and " adits." If the under-ground passage is See also:vertical it is a See also:shaft; if the shaft is begun at the surface the operations are known as " sinking "; and it is called a " rising" if worked upwards from a previously constructed heading or See also:gallery
.
Tunnelling has been effected by natural forces to a far greater extent than by See also:man
.
In See also:limestone districts innumerable See also:swallow-holes, or shafts, have been sunk by the See also:rain See also:water following See also:joints and dissolving the See also:rock, and from the bottom of these shafts tunnels have been excavated to the sides of
hills in a manner strictly analogous to the See also:ordinary method of executing a tunnel by sinking shafts at intervals and driving headings therefrom
.
Many See also:rivers find thus a course under-ground
.
In See also:Asia See also:Minor one of the rivers on the route of the See also:Mersina railway See also:extension pierces a See also:
Where the See also:Atlantic rollers break on the See also:west See also:coast of See also:Ireland, or on the seaboard of the western See also:Highlands of See also:Scotland, numberless caves and tunnels have been formed in the cliffs, beside which artificial tunnelling operations appear insignificant
.
The most gigantic subaqueous demolition hitherto carried out by man was the blowing up in 1885 of See also:Flood Rock, a See also:mass about 9 acres in extent, near Long See also:Island See also:Sound, New See also:York
.
To effect this gigantic See also:work by a single instantaneous blast a shaft was sunk 64 ft. below sea-level, from the bottom of which 4 M. of tunnels or galleries were driven so as to completely See also:honeycomb the rock
.
The roof rock ranged from to ft. to 24 ft. in thickness, and was supported by 467 pillars 15 ft. square; 13,286 holes, averaging 9 ft. in length and 3 ins. in See also:diameter, were drilled in the pillars and roof
.
About 8o,000 cub. yds. of rock were excavated in the galleries and 275,000 remained to be blasted away
.
The holes were charged with 110 tons of " rackarock," a more powerful explosive than See also:gunpowder, Which was fired by See also:electricity, when the sea was lifted too ft. over the whole See also:area of the rock
.
Where natural forces effect analogous results, the holes are bored and the headings driven by the chemical and See also:mechanical action of the rain and sea, and the explosive force is obtained by the expansive action of See also:air locked up in the fissures of the rock and compressed to many tons per square See also:foot by impact from the waves
.
Artificial breakwaters have often been thus tunnelled into by the sea, the compressed air blowing out the blocks and the waves carrying away the debris
.
With so many examples of ,natural caves and tunnels in existence it is not to be wondered at that tunnelling was one of the earliest See also:works undertaken by man, first for dwellings and tombs, then for See also:quarrying and mining, and finally for water-See also:supply, drainage, and other requirements of See also:civilization
.
A Theban See also:
See also:Flinders See also:Petrie has traced the method of underground quarrying followed by the Egyptians opposite the Pyramids
.
Parallel galleries about 20 ft. square were driven into the rock and See also:cross galleries cut, so that a See also:
No See also:practical advance was made on the tunnelling methods of the Romans until gunpowder came into use
.
Old engravings of mining operations See also:early in the 17th century show that excavation was still accomplished by pickaxes or See also:hammer and chisel, and that See also:wood fires were lighted at the ends of the headings to split and soften the rock in advance (see fig
.
1)
.
(From See also:
In 1830 See also:Lord Cochrane (afterwards loth See also:earl of See also:Dundonald) patented the use of compressed air for shaft-sinking and tunnelling in water-bearing strata
.
Water under any pressure can be kept out of a subaqueous chamber or tunnel by. sufficient air of a greater pressure, and men can breathe and work therein—for a time—up to a pressure exceeding four atmospheres
.
The shield and cast-iron lining invented by Brunel, and the compressed air of Cochrane, have with the aid of later inventors largely removed the difficulties of subaqueous tunnel-See also:ling
.
Cochrane's process was used for the See also:foundation of See also:bridge piers, &c., comparatively early, but neither of these devices was employed for tunnelling until See also:half a century after their invention
.
Two important subaqueous tunnels in the construction of which neither of these valuable See also:aids was adopted are the Severn and the See also:Mersey tunnels
.
The Severn tunnel (fig
.
16), 41 M. in length for a See also:double See also:line of railway, begun in 1873 and finished in 1886, See also:Hawkshaw, Son, See also:Hayter & See also:Richardson being the See also:engineers and T
.
A
.
See also: In 1879 the works were flooded for months by a See also:land spring on the Welsh side of the river, and on another occasion from a hole in the river bed at the See also:Salmon See also:Pool . This hole was subsequently filled with See also:clay and the works completed beneath . Two preliminary headings were driven across the river to test the ground . See also:Bleak-ups " were made at intervals of two to five chains and the arching was carried on at each of these points . All parts of the excavation were timbered, and the greatest amount excavated in any one See also:week was 6000 cub. yds . The See also:total amount of water raised at all the pumping stations, is about 27,000,000 gallons in twenty-four See also:hours . The length of the Mersey tunnel (fig . 15) between See also:Liverpool and See also:Birkenhead between the pumping shafts on each side of the river is one mile . From each a drainage heading was driven through the sandstone with a rising gradient towards the centre of the river . This heading was partly bored out by a See also:Beaumont See also:machine to a diameter of 7 ft . 4 in. and at a See also:rate attaining occasionally 65 lineal yds. per week . All of the tunnel excavation, amounting to 320,000 cub. yds., was got out by See also:hand labour, since heavy See also:blasting would have shaken the rock . The minimum cover between the top of the See also:arch and the bed of the river is 3o ft . Pumping machinery is provided for 27,000,000 gallons per day, which is more than double the usual quantity of water . Messrs Brunlees & See also:Fox were the engineers, and Messrs Waddell the contractors for the works, which were opened in 1886, about six years after the beginning of operations . In 1869 P . W . See also:Barlow and J . H . See also:Greathead built the See also:Tower foot-way under the Thames, using for the first time a cast-iron lining and a shield which embodied the See also:main features of Brunel's See also:design . Barlow had patented a shield in 1864, and A . E . See also:Beach one in 1868 . The latter was used in a short masonry tunnel under Broadway, New York See also:City, at that time . In 1874 Greathead designed and built a shield, to be used in connexion with compressed air, for a proposed See also:Woolwich tunnel under the Thames, but it was never used . Compressed air was first used in tunnel work by See also:Hersent, at See also:Antwerp, in 1879, in a small See also:drift with a cast-iron lining . In the same See also:year compressed air was used for the first time in any important tunnel by D . C . Haskin in the famous first See also:Hudson River tunnel, New York City . This was to be of two tubes, each having See also:internal dimensions of about 16 ft. wide by 18 ft. high . The excavation as fast as made was lined with thin See also:steel plates, and inside of these with brick . In See also:June 188o the northerly tube had reached 36o ft. from the See also:Hoboken shaft, but a portion near the latter, not of full See also:size, was being enlarged: Just after a See also:change of shifts the compressed air blew a hole through the soft silt in the roof at this spot, and the water entering drowned the twenty men who were working therein . From time to time See also:money was raised and the work advanced . Between 1888 and 1891 the northerly tunnel was extended 2000 ft. to about three-fourths of the way across, with See also:British See also:capital and largely under the direction of British engineers—See also:Sir See also:Benjamin See also:Baker and E . W . See also:Moir .
Compressedair and a shield were used, and the tunnel walls were made of bolted segments of cast iron
.
The money being exhausted, the tunnel was allowed to fill with water, and it so remained for ten years: Both tubes were completed in 1908
.
The use of compressed air in the Hudson tunnel, and of See also:annular See also:shields arid cast-iron lined tunnel in constructing the City & South London railway (1886 to 189o) by Great-See also:head, became widely known and greatly influenced subaqueous and soft-ground tunnelling thereafter
.
The pair of tunnels for this railway from near the See also:Monument to Stockwell, from 10 ft
.
2 in. to 10 ft
.
6 in. interior diameter, were constructed mostly in clay and without the use of compressed air, except for a comparatively short distance through water-bearing gravel
.
In this gravel a timber heading was made, through which the shield was pushed
.
The reported total cost was £84o,o0o
.
Among the tunnels constructed after the City & South London work was well advanced, lined with cast-iron segments, and constructed by means of annular shields and the use of compressed air, were the St Clair (See also:Joseph Hobson, engineer) from See also:Sarnia to See also:Port See also:Huron, 1889-1890, through clay, and for a short distance through water-bearing gravel, 6000 ft., 18 ft. internal diameter; and the notable Blackwall tunnel under the Thames (Sir See also: 6 in. long, contained a bulkhead with movable shutters, as foreshadowed in Baker's See also:pro-posed shield (fig . 2) . Numerous tunnels of_~ small diameter have !=,A' t;•, = }i been similarly See also:con- structed under the Thames and See also:Clyde for -L. w e= s ---t s r electric and See also:cable r = r , : 'e : e `, ways, several for sewers in See also:Melbourne, and two under the See also:Seine at See also:Paris for See also:sewer siphons . The Rotherhithe tunnel, under the Thames, for a road-way, with a length of 4863 ft. between portals, of which about 1400 ft. are directly under the river, has a t _- seen= largest cross : y r ~ section of any sub- -e %~%%% eseeet aqueous tube of this FIG . 2.—B . Baker's pneumatic shield•. type in the world (see fig . 3) . It was begun in 1904 and finished in 1908, See also:Maurice Fitzmaurice being the engineer of design and construction, and See also:Price & See also:Reeves the contractors . It penetrates sandy and Shelly clay overlying a seam of limestone beneath which are pebbles and loamy See also:sand . A preliminary tunnel for exploration, 12 ft. in diameter, was driven across the river, the top being within 2 ft. of the following main tunnel . The top of the main tunnel excavation in the See also:middle of the river was only 7 ft. from the bed of the Thames, and a temporary blanket of filled earth, usually allowed in similar cases, was prohibited owing to the See also:close proximity of the docks . The maximum progress in one day was 12.5 ft., and the See also:average in six days 10.4 ft . The air compressors were together capable of supplying 1,000,000 cub. ft. of air per See also:hour . Some tunnels of marked importance of this type—to be operated solely with electric cars—have been built under the East and Hudson rivers at New York . Two tubes of 15 ft. interior diameter and 4150 ft. long penetrate See also:gneiss and gravel directly under the East River between the See also:Battery and See also:Brooklyn . They were begun in 1902, with Wm . B . See also:Parsons and See also:George S . See also:Rice as engineers, and were finished in See also:December 1907, under the direction of D . L . Hough of the See also:Detroit Hirer Tunnel. tubes . River Seine, See also:Park. t tube Scale of Feet t0 20 3 ? ro S 0 Frc . 3.-Cross Sections of Tunnels under Rivers and Harbours . 
New York Tunnel See also:Company . They carry subway trains . In one of the See also:blow-outs of compressed air a workman was blown through the gravel roof into the river above . He lived until the next day . Two other tubes of the same size built also through gneiss and gravel between 1905 and 1907 by the Degnon Contracting Company, with R . A . Shailer as the contractors' engineer, go from 42nd See also:Street to Long Island City . Four much larger tubes (see fig . 3) built in 1904 to 1909, for the See also:Pennsylvania railroad, with See also:Alfred See also:Noble as See also:chief engineer, S . Pearson & Son as contractors, and E . W . Moir as See also:general manager, cross from 32nd and 33rd Streets to Long Island .
The maximum average progress per day (one heading) for the best See also:month's work was: rock, 4.1 ft.; rock and earth, 3.8 ft.; earth, with full sand See also:face, 12.8 ft
.
The best methods of preventing blow-outs were found to consist of employing clay blankets (sometimes 25 ft. thick) on the river bed, which could be carried up to 20 ft. depth of water, and of filling the pores of the sand and gravel with See also:blue See also:lias See also:lime or See also:cement grout
.
The maximum air pressure was 38 lb per sq. in
.
In the See also:case of sand face with poor leaky cover the usual practice was to make the air pressure equal to that of water from the surface down to about a See also:quarter the distance below the top of the shield
.
The average amount of See also:free air supplied per man per hour was approximately 2300 cub. ft
.
On the Hudson river side two tubes of the same size as those in the East river are for the Pennsylvania trains to New See also:Jersey
.
Two tubes from See also:Morton Street to New jersey, begun by Haskin, already referred to, are for subway trains, and so are the most southerly of all on the Hudson side, viz. the two from Cortlandt Street to under the Pennsylvania station in Jersey City
.
The two tubes from Morton Street were completed under the direction of See also: A large proportion of the silt which under ordinary processes would be taken into the tunnel through the shield, carried to the See also:shore and got rid of by expensive methods, was by the latter process merely displaced as the shield with nearly or quite closed See also:diaphragm was pushed ahead . The East See also:Boston tunnel, the first important example of a shield-built monolithic See also:concrete arch, from the Boston Sub-way to East Boston, is 1.4 M. long, 3400 ft. being under the See also:harbour . One mile was excavated by tunnelling with roof shields about 29 ft. wide, through clay containing pockets of sand and gravel . The engineer was H . A . See also:Carson, and the contractors the Boston Tunnel Construction Company and See also:Patrick McGovern . Some 25 M. of waterworks brick-lined tunnels have been built since 1864, mostly in clay, under the Great Lakes, without the use of shields, though in the later ones compressed air was utilized . A large portion of the latest See also:Cleveland tunnel, 9 ft. interior diameter, was built at the rate of 17 ft. per day at a cost of about 818 per ft . During this work three explosions of inflammable gases occurred, in which nineteen men were killed and others were injured . Later a See also:fire at the shaft in the lake caused the death of ten men . Work was thereafter completed under the See also:engineering direction of G . H . Benzenberg . Less serious accidents, principally explosions of See also:marsh See also:gas, occurred in many of the other tunnels . In one case (at See also:Milwaukee under Benzenberg) drift material was penetrated, with large boulders and coarse and See also:fine gravel, and without any sand or clay filling, apparently in See also:direct communication with the lake bottom . At times the necessary air pressure was 42 lb per sq. in . Subaqueous Tunnels made by sinking Tubes, Caissons, &'c.—ln 1845 De la Haye, in England, doubtless having in mind thetedious and difficult work of the Thames tunnel, proposed to make tunnels under water by sinking large tubes on a previously prepared bed and connecting them together . Since then many inventors have proposed similar schemes . In 1866 Belgrand sank twin See also:plate-iron pipes, 1 See also:metre diameter and 156 metres long, under the Seine at Paris for a sewer See also:siphon, and there have since been numerous examples of sunk cast-iron subaqueous water-pipes . It is believed that the first tunnel of this class, large enough for men to move upright in, was by H . A . Carson, assisted by W . See also:Blanchard and F . D .
See also: |