Mont Cenis Tunnel

“ It is famous for the winding road constructed by Napoleon I., which leads over it from France to Italy, and for an immense railway tunnel, which, after nearly 14 years' labor, was finished in 1871. The tunnel does not actually pass through the mountain, but through the Col de Fréjus, about 15 miles to the S. W., where it was found possible to construct it at a lower level. The Mont Cenis Pass is 6,765 feet above the level of the sea, whereas the elevation of the entrance to the tunnel on the side of Savoy is only 3,801 feet, and that on the side of Piedmont 4,246 feet. ”

“ Mont Cenis Railway.—Pending the completion of the great Mont Cenis tunnel, a temporary railway on inclined planes is to be carried along the present road over the mountain. The French Government, on its portion of the line, will use locomotives with a peculiar mechanism, to produce adhesion, on a middle rail placed between the two ordinary rails. On the Italian side a traction carriage will be employed, which will wind the carriages up by means of a drum acting on a heavy fixed cable laid along the line. ”

“ It will be seen at once that the problem was quite different from that of boring fifteen feet under the Thames, and sometimes through watery mud. In boring through mountains the quickest way of cutting and carting away rock is one of the chief points to be considered. At the Mont Cenis Tunnel the blasting took place by driving a series of shot holes into the soil, all over the surface to be cut, filling them with explosives, and firing them simultaneously in rings. Such explosives may be fired by a time-fuse or by electricity, giving the workmen ample time to escape out of reach. ”

“ As a tunnel, Mont Cenis is of no very extraordinary length; but, being composed of almost solid rock, the boring operation for so great a distance must have proved exceedingly difficult, the width being twenty-six feet, and the height nineteen feet. Some 2000 men were constantly employed at each end for nearly nine years. The steep ascent, of some 8000 feet, is another marvellous feature. ”

“ Mons' undertaking, we may, in the first place, state that in its progress the tunnel must pass under some of the most elevated crests of Mont Cenis,—one, in particular, where there will be 4,850 feet of mountain, capped with eternal glaciers, over head, at the middle of the tunnel, so that not only will the workmen and machinery in construction, and the passengers and trains in transit, be buried to that depth in the heart of the mountain, but all idea of shafts, either to facilitate excavation, or to promote ventilation, must be out of the question. ”

“ The summit of this tunnel is 990 feet below the surface at Andermatt, and 6600 feet beneath the peak at Kastelhorn of the St. Gothard group. The tunnel itself is 261⁄2 feet wide, and 19 feet 10 inches from the floor to the crown of the arched roof. Its length is 91⁄2 miles, while the Hoosac Tunnel, on the Fitchburg Railway, is 41⁄2 miles long. The Mont Cenis tunnel is one and five-eighths miles shorter than that of St. Gothard.
Impatient.—1. All communications intended for this paper should be addressed to "James Elverson, Publisher of Golden Days, Philadelphia, Pa." ”

“ It is hardly necessary to say that the great rival to the Mont Cenis or Summit Railway is the railway that is to be laid through the tunnel, which, in the official documents of both France and Italy is denominated “The Great Tunnel of the Alps.” But before we enter upon the description of this tunnel, an account of subterraneous construction from the earliest period we have been able to trace tunnels, may not be uninteresting.
Tunnelling through hills and mountains is not exactly “as old as the hills,” but the practice, nevertheless, is of great antiquity. ”

“ It should be remembered, moreover, that in working a gallery of this kind, where vertical shafts are impossible, by manual labor, a powerful and costly air-compressing apparatus would have been necessary for the ventilation of the tunnel alone, so that the economy of the system, as applied at the Mont Cenis over the general system of tunnelling in hard rock, is evident. I propose, in the second portion of this article, to give a short description of the machinery employed and the system of working adopted, both at the South and North ends of the Mont Cenis gallery. ”

“ He adds: "We are clearly a progressive race, and it would be a wise brain that could predict with certainty what advance may be made by some live Yankee in tunneling machinery when we come to cut a ship-tunnel." [4] Mr. Evans was, We may remember, like Major Shelbourne, in favor of the San Blas route, and the tunnel which that route involves.
Certain details as to the machinery used in the Alps may be of interest. After hand-drilling was given up, all the drills used were run by compressed air, but the methods employed to compress it varied. At Mont Cenis hydraulic power exclusively was used. ”

“ Equally remarkable and extensive were the labours connected with the preparatory works. New and solid roads, bridges, canals, magazines, workshops, forges, furnaces, and machinery had to be constructed; residences had to be built for the men, and offices for the engineers; in fact, at each extremity of the tunnel a complete establishment had to be formed. Those who153 have traversed Mont Cenis since the works began have been perplexed by the strange appearance and character of the machinery and establishments to be seen at Modane and Fourneau. ”

“ Of course the tunnel must be continually supplied with fresh air along its whole length, as well as at the heading. This is easily done from the compressed air tube in the covered drain.
The whole length of the Mt. Cenis tunnel is through rock varying in hardness, and veined throughout with quartz. In many parts it is liable to flake off, and in some places considerable masses have broken away during the construction. ”

“ Huge wood fires are made up against the face of the rock, which becomes shattered and traversed by cracks, and when cooled, it is easily detached with a pick or fork. Of late years, however, machines have been devised for boring or breaking the rock. Some form a hole by the continuous motion of a rotating drill, others by means of intermittent blows. One of these rock-boring machines, manufactured by Messrs Turner, of Ipswich, performs its work by a combination of both these operations. By the employment of these machines, the formation of the tunnel under Mount Cenis was greatly facilitated. ”

“ The Cenis tunnel, 71⁄2 miles in length, occupied some 13 years to complete, while some 8 years were required to drive 91⁄4 miles through the St. Gotthard. This was an achievement of which those engaged in the task were justly proud. Indeed, the Austrians hold a unique position in the rapidity with which they can drive these gigantic undertakings through the most formidable mountain chains.
The section of railway upon which this tunnel is situated sorely tried the ingenuity of the engineers up to the Paznaun valley. ”

“ J. B. Fell patented a locomotive designed for working over extremely steep gradients. At that time there was a break 47 miles long in the continuity of the iron road communication between France and Italy by the Mount Cenis route. This break has in later years been abolished by the construction and working of the famous Mount Cenis tunnel. Brassey and Co. in 1863 proposed that during the construction of the tunnel a temporary mountain railway worked on Fell’s system should be built over the mountain. An experimental locomotive was, therefore, constructed at the Canada Works, Birkenhead. ”

“ The construction of this subterranean road employed the labour of above a thousand men for nearly four years. Besides excavating the arch out of a solid rock, they used 23,000,000 of bricks, and 8000 tons of Roman cement in the building of the tunnel. Thirteen stationary engines, and about 100 horses, were also employed in drawing the earth and stone out of the shafts. Its entire length is 2869 yards, or nearly 13⁄4 mile—exceeding the famous Kilsby Tunnel by 471 yards.
The Midland Railway was a favourite line of Mr. Stephenson’s for several reasons. ”

“ When the rock is fissured or disintegrated and the roof of the excavation at the front requires timbering, the shield should be kept closer to the front. In this way the quantity of timber for strutting is greatly reduced, so lessening the probabilities of fires. It is very difficult, in compressed air, to extinguish fires and in almost every instance the only way is to flood the tunnel. This was done at the Manhattan end of the tunnel under the East River for the extension to Brooklyn of the New York Subway. ”

“ In the construction of railroads it is frequently necessary to pierce the hills, so as to preserve a line of road as nearly level as practicable. The method of proceeding with tunneling depends mainly upon the kind of material to be excavated. This having been generally ascertained by borings and trial shafts, the work is commenced by sinking the working shafts, which must be sufficiently capacious to admit readily of lowering men and materials, raising the material excavated, fixing pumps, and also for starting the heading of the intended tunnel when the required depth is reached. ”

“ 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. ”

“ It occasionally happens when filling-in is to take place in the future, or where landslides are liable to bury the tracks, that a railway tunnel has to be built on the surface of the ground. In such cases the construction of the tunnel consists simply in building the lining of the section on the ground surface with just enough excavation to secure the proper grade and foundation. Generally the lining [201] is finished on the outside with a waterproof coating, and is sometimes banked and partly covered with earth to protect the masonry from falling stones and similar shocks from other causes. ”

“ They never quite removed the machine from the heading when they were finished, but it was maintained right up to the outbreak of the Second World War, when it became derelict."
Adams and I walked back to the car. As we did so, he revealed himself as being pro-tunnel. "It's a tragic thing, this tunnel business, I think. If the tunnel had been built forty or fifty years ago, just think of what an asset to Europe it would have been," he said. We packed ourselves in, and Burgess drove us down a very rough, narrow road to the level of the railroad line. ”

“ When the Great Spring broke in and drowned the tunnel in October, 1879, the distance from the shaft to the face of the heading under the river was 10,100 feet, or more than a mile and three-quarters. All the skips were brought out by men pushing them that distance, the men being known as ‘runners Progress of the work—1881. out.’ These ‘runners out’ had very short lengths to push the skips, and the cost, when the Company was working the heading, was more than ten times what it could have been done for by ponies, or perhaps twenty times what it could have been done for by proper hauling-engines. ”

“ In reasonably stable material, like compact-clay, the front face will usually stand alone for the short time necessary to excavate the section and advance the shield one stage. In softer material the face can usually be sustained for the same short period by means of compressed air; or the face of the excavation, instead of being made vertical, can be allowed to assume its natural slope. In the latter case a visor-shaped front-end construction, such as was used on some portions of the Clichy tunnel, is particularly advantageous. ”

“ The character of the difficulties encountered in performing this duty will depend upon the depth at which the tunnel is driven. In constructing shallow tunnels by the cut-and-cover method care has to be taken first of all not to disturb the street traffic any more than is absolutely necessary. This condition precludes the single trench method of open cut tunneling in all places where the street traffic is at all dense, and compels the engineer to use the methods employed in Paris and New York, as previously described, or else the transverse trench or slice method employed in the Boston Subway. ”

“ When this was completed, the pumps were started again, and the clay was found to have effectually stopped the water.
At each end of the lengths of brickwork, where the water had broken in, a 6-ft. length of tunnel was immediately commenced, 4 feet thick; the ordinary work being only 2 feet 3 inches. These lengths were taken out as rapidly as possible, and brickwork in cement built in them, thus forming, in the chases which had been cut, a ring of brickwork nearly double the ordinary thickness to stop the water from travelling along the back of the work. ”

“ In working them, no process is more costly than that of tunneling. It is also not unfrequently the most discouraging. This is especially true of those mines that can only be prospected by means of a tunnel, as was the case with the Blue Gravel Mine. ”

“ 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. ”