Tunnel (underground)

“ Open-cut tunnels are those driven at such a small depth under the surface that it is more convenient to excavate an open cut, build the tunnel masonry inside it, and then refill the open spaces, than it is to carry on the work entirely underground. In firm soils the usual mode of operation is to excavate first two parallel trenches for the side walls, then remove the core, and build the arch and the invert. In unstable soils, since the invert must be built first, it is usual to open up a single wide trench. ”

“ We'll have to start in the dark," he went on, referring to the black tunnel that stretched under Snake Mountain. "But we may come out into the light. Anyhow, we're going in!"
CHAPTER XX INTO THE DEPTHS
Preparations for exploring the mysterious tunnel on this occasion were much more complete and elaborate than when Bud, Dick and Nort walked through it before. And they did not rush off in haste, the moment it was discovered that the water no longer came through the reservoir end of the pipe line that formed the beginning and end of the old underground stream course. ”

“ The guiding precept of the exhibit has not been to outline exhaustively the entire history of tunneling, but rather to show the fundamental advances which have occurred between primitive man’s first systematic use of fire for excavating rock in mining, and the use in combination of compressed air, iron lining, and a movable shield in a subaqueous tunnel at the end of the 19th century. ”

“ There are two important secondary techniques for opening subterranean and subaqueous ways, neither a method truly of tunneling. One of these, of ancient origin, used mainly in the construction of shallow subways and utility ways, is the “cut and cover” system, whereby an open trench is excavated and then roofed over. The result is, in effect, a tunnel. The concept of the other method was propounded in the early 19th century but only used practically in recent years. ”

“ In tunneling hard, firm rock, this is practically the entire compass of the work: breaking away the rock from the mother mass, and, coincidently, removing it from the workings. The opposite extreme in conditions is met in the soft-ground tunnel, driven through material incapable of supporting itself above [204] the tunnel opening. ”

“ Clang, clang, clang, we passed right under the thumping levers of another vast machine, and so came at last to a wide tunnel, in which we could even hear the pad, pad, of our shoeless feet, and which, save for the trickling thread of blue to the right of us, was quite unlit. The shadows made gigantic travesties of our shapes and those of the Selenites on the irregular wall and roof of the tunnel. Ever and again crystals in the walls of the tunnel scintillated like gems, ever and again the tunnel expanded into a stalactitic cavern, or gave off branches that vanished into darkness. ”

“ At the bottom of this shaft, 163 feet below the surface of the ground, the mouth of the tunnel was reached, and the visitors took their seats on small tramcars which were drawn by workmen. So evenly has the boring machine done its work that one seemed to be looking along a great tube with a slightly downward set, and as the glowing electric lamps, placed alternately on either side of the way, showed fainter and fainter in the far distance, the tunnel, for anything one could tell from appearances, might have had its outlet in France. ”

“ Tunnelling has been effected by natural forces to a far greater extent than by man. In limestone districts innumerable swallow-holes, or shafts, have been sunk by the rain water following joints and dissolving the rock, and from the bottom of these shafts tunnels have been excavated to the sides of hills in a manner strictly analogous to the ordinary method of executing a tunnel by sinking shafts at intervals and driving headings therefrom. ”

“ The Park Ave. construction (Fig. 120) consists of two parallel double-track tunnels, located on each side of the street, and about 10 ft. below the present tunnel. The soil being composed of good rock, the tunnels were driven by a wide heading, and one bench, since no strutting was required, and the masonry lining, even of the roof, was left far behind the front of the excavation. The masonry lining consists of concrete walls and brick arches. ”

“ It is well known that about 35 years ago an attempt was made to construct a tunnel under the North River by using a "Pilot" system under compressed air and forming the tunnels in brick masonry. Owing to the very soft nature of the materials through which it passed, several serious accidents occurred, and the work was abandoned after about 2,000 ft. of tunnel had been constructed. Later, this work was taken up again, when a shield was installed and an additional 1,800 ft. ”

“ Trains coming through the tunnel from France were to emerge into the daylight and the ordinary open air of England either from a four-mile-long access tunnel connected to the South-Eastern's railway line at Abbots Cliff or—this was a favored alternative plan of Sir Edward's—at Shakespeare Cliff via a station to be constructed in a great square excavated a hundred and sixty feet deep in the ground, which would be covered over with glass, lighted by electric light, and equipped "with large waiting rooms and refreshment rooms." ”

“ The experience then in the construction of this tunnel led capitalists and engineers to believe that, owing to the very soft nature of the ground, a tunnel could not be built that would be sufficiently stable to withstand the vibration due to heavy traffic, and for this reason tunnels under the North River were not looked upon as practicable. ”

“ A tunnel, defined as an engineering structure, is an artificial gallery, passage, or roadway beneath the ground, under the bed of a stream, or through a hill or mountain. The art of tunneling has been known to man since very ancient times. A Theban king on ascending the throne began at once to drive the long, narrow passage or tunnel leading to the inner chamber or sepulcher of the rock-cut tomb which was to form his final resting-place. Some of these rock-cut galleries of the ancient Egyptian kings were over 750 ft. ”

“ During construction, however, special means will have to be provided for removing the water from the excavation, their character depending upon the method of excavation and upon the grades of the tunnel bottom. When the excavation is carried on from the entrances only, unless the tunnel has a descending grade from the center toward each end, the tunnel floor in one heading will be below the level of the entrance, or, in other words, the descending grade will be toward the point where work is going on, while at the opposite entrance the grade will be descending from the work. ”

“ The heading of the tunnel, shown on Plate XII., like that of the Hoosac, was driven to the full width of the tunnel. It is clear from theoretical considerations, and experience has confirmed the conclusions, that the method of taking, with machine drills, the whole width of the excavation at once conduces to rapidity of advance, and to economy of explosive. ”

“ Refuge niches are usually spaced from 60 ft. to 100 ft. apart, while the larger storage niches may be located as far as 3000 ft. apart. The niche construction shown by Fig. 48 is that employed on the St. Gothard tunnel.
Entrances. —The entrances, or portals, of tunnels usually consist of more or less elaborate masonry structures, depending upon the nature of the material penetrated. In soft-ground tunnels extensive wing walls are often required to support the earth above and at the sides of the entrance ”

“ The Times wrote that, unless it was much mistaken, "the publication of the Blue Book will be found to have closed the whole question of the Channel Tunnel for a long time to come."
Undermined by land, overmined at sea, sluice-ridden at its entrance, and liable to asphyxiating vapors at intervals, the Tunnel will hardly be regarded by nervous travellers as a very pleasant alternative even to the horrors of seasickness....
The whole system of defense must forever be [85] at the mercy of blunderers, criminals, and madmen. ”

“ Occasionally favourable opportunities present themselves for making horizontal shafts. For a portion of its length the tunnel may be located at no very great distance from the precipitous sides of some deep mountain ravine, or run near to the cliffs on the sea-coast, and advantage can be taken to drive a lateral heading or gallery through which the material from the tunnel excavation may be conveyed and thrown out into the gorge or seashore below. ”

“ At intervals of about 300 ft. throughout each tunnel, alignment pockets are formed in the concrete arch, also above the bench, on the south bench of the North Tunnel and the north bench of the South Tunnel. In each pocket is placed a graduated and verniered brass bar, so that, when the base line is projected on these bars, the lateral movement of the tunnel can be read directly. ”

“ The entrance to the great tunnel is within a few yards of Geschenen Station. When we consider that this is the longest tunnel in the world (from Geschenen to Airolo, nearly nine and a half miles) , and that the rock which is pierced consists of such hard material as quartz and granitic gneiss, the work may well claim to be one of the great engineering feats of the century. ”

“ This exit, heading away from the concealed abysses, had in some ages past been made by man into a doorway.
Passing through this secret portal the passage is confined for some distance by narrow walls, and the low roof makes it necessary in places to crawl upon the knees. The tunnel ends by opening into a vast cavern similar to the one first entered; but on advancing the walls and ceilings grow invisible to the light of torches and it becomes like a vast field. ”

“ When the whole section is filled by the fallen material, the problem may be considered as the excavation of a new tunnel of short length inside the old tunnel, and under rather more difficult conditions. The first task, particularly if men have been imprisoned behind the fallen material, is to open communication through it between the two uninjured portions of the tunnel. It is advisable to do this even when there is no danger to life because of imprisoned workmen, since it enables the work of repairing to be conducted from both directions. ”

“ Colonel Yolland also mentioned in his report that during his previous visit, on July 15, "I had an escape from what might have been a serious accident. The wet chalk in the bottom of the tunnel, between and outside the rails of the tramways, is so slippery and greasy that it is almost impossible to keep on one's feet ”

“ The many and elaborate plans for defending the Tunnel and rendering it useless are themselves the best arguments against its construction. Whatever advantages or gains are to be derived from it, and these I will not discuss, they are all as nothing in comparison of the disadvantages. The Tunnel if made would be not the messenger of peace and good-will, but the harbinger and forerunner of increased military expenditure, of panics and apprehensions, of possible invasions, strife and bloodshed, and asking once more the question with which I commenced, "Shall we have a Channel Tunnel?" ”

“ About 350 men, a locomotive, forty cars, 200 horse water power, machinists, blacksmiths a legion, for sharpening drills is hand work, so is picking up rock, loading cars, making track, and all this is done in the smoky, wet, grimy, confined tunnel, or round about its entrance, and you have a mixed, confused suspicion that this tunnel driving is a work needing high powers of organization ”

“ About it were clustered drills that were eaten by age and the dampness of the seepage; farther on a "skip", or shaft-car, lay on its side, half buried in mud and muck from the walls of the tunnel. Here, too, the timbers were rotting; one after another, they had cracked and caved beneath the weight of the earth above, giving the tunnel an eerie aspect, uninviting, dangerous. Harry peered ahead.
"It ain't as bad as it looks," came after a moment's survey. "It's only right 'ere at the beginning that it's caved. But that does n't do us much good." ”

“ The roof, as a rule, is supported by longitudinal planks held in position by five or seven segments of arched frames placed across the tunnel. A large quantity of timber and carpenter work is thus entirely wasted and these costly items, in many cases, make the concrete [76] lining of a tunnel more expensive than the one built of brick and stone. To avoid these inconveniences tunnels have been successfully lined with concrete on the side walls and concrete blocks in the arches. These blocks have been built by hand and molded in the shape of the arch voussoirs. ”

“ This, Adams said, was to reinforce the tunnel at the point where it passed underneath the railway line. We went on again, this time walking on a dirt floor, and then we came to a timbered junction, from which the tunnel branched off again to the right in the north-east direction that was originally intended to bring it into line with the gallery at Shakespeare Cliff, while to the left there was a low-roofed chamber that probably once housed a siding and a maintenance workshop for the Beaumont boring machine. ”

“ A truck is now brought up, and four men clear a passage in front, through the heap of débris, two with picks and two with shovels, while on either side and behind are as many men as space will permit. The stone is thrown either to the sides of the heading or into the wagon, shoveling being greatly aided by the steel flooring, which, before the explosion, had been laid over the rails for nearly 10 yds. down the tunnel to receive the falling rock. ”