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1608, a tunnel which at that period was points during many years. a very bold piece of engineering. It stances were those by which traffic was was designed to drain the Valley of carried across the Alleghany Mountains, Mexico, which has no natural outlet. connecting on each side with the PennThis tunnel was more than six miles sylvania railway lines. These old planes long and ten feet wide. It was driven through the formation called tepetate, a peculiar earth with strata of sand and marl. It was finished in eleven months. At first excavated without a lining, it was afterward faced with masonry. It was not entirely protected when a great flood came, the dikes above gave way, and the tunnel became ob
The Nochistongo Cut, Mexican Central Railway. structed. The City of Mexico was flooded, and it was are still visible from the present Penndecided that, instead of repairing the sylvania Railroad where it crosses the tunnel an open cut should be made. summit west of Altoona. The planes The engineer who had constructed the were operated by stationary engines tunnel, Enrico Martinez, was put in acting upon cables attached to the cars. charge of this enormous undertaking, These cables passed around drums at and others took his place after his the head of the planes, the weight of the death. The cut is believed to be the cars on one track partially balancing largest ever made in the world. For those on the other. Similar planes were more than a century the work was con- in use also at Albany, Schenectady, and tinued. Its greatest depth is now 200 other places. feet. It was cut deeper, but has par Another effective expedient is the tially filled with the washings from the central rack rail. No better or more slopes. The cost was enormous, more successful example of this method of conthan 6,000,000 dollars in silver having struction can be given than the Mount been actually disbursed ! Wages for Washington Railway [illustrated p. 12]. workmen were then from 9 to 12 cents The road was completed in 1869. Its a day. All convicts sentenced to hard length is 34 miles and its total rise 3,625 labor were put at work in the great cut. feet. Its steepest grade is about 1 foot The loss of life was very great. Writers rise in every 3 feet in length; the averof the time state that more than 100,000 age grade is 1 in 4. It is built of heavy Indians perished while engaged in the timber, well bolted to the rock. Low work.
places are spanned by substantial trestle
work. The gauge of the road is 4 feet When a line of railway encountered a 7} inches, and it is provided with the grade too steep for ascent by the trac- two ordinary rails and also the cention of the locomotive, the earlier en- tral rack rail, which is really like an gineers adopted the inclined plane. iron ladder, the sides being of angle Such planes were in use at important iron and the cross-pieces of round iron
14 inch in diameter and 4 inches apart. Into these plays the central cog-wheel on the locomotive, which thus climbs this iron ladder with entire safety. Very complete arrangements are made to prevent the descent of the train in case of
accident to the machinery. The locomotive is always below the train, and pushes it up the mountain. Many thousands of passengers have been transported every year without accident.
The rack railroad ascend
ing the Righi, in Switzerland, was copied after the Mount Washington line. Some improvements in the construction of the rack rail and attachments have been introduced upon mountain roads in Germany, and this system seems very advantageous for use in exceptionally steep locations.
When a line of railway meets in its course a barrier of rock, it is often best to cut directly through. If the grade is not too far below the surface of the rock, the cut is made like a great trench with
the sides as steep as the nature The Mount Washington Rack Railroad.
of the material will allow. Very
deep cuts are, however, not desirable. The rains bring down upon their slopes the softer material from above, and the frost detaches pieces of rock which, falling, may result in serious accidents to trains. Snow lodges in these deep cuts, at times entirely stopping traffic, as in the recent experience near New York. A tunnel, therefore, while perhaps greater in first cost than a moderately deep cut, is really often the more economical expedient.
And here is as good a place, perhaps, as any other in this article, to say that true engineering is the economical adaptation of the means and opportunities existing, to the end desired. Civil engineering was defined. by one of the greatest of England's engineers, as “the art of directing the great sources of power in nature for the use and convenience of man," and that definition adopted as a fundamental idea in the charter of the English Institution of Civil Engineers. But the development of engineering works in America has been
Trestle on Portiand and Ogdensburg Railway, Crawford Notch, White Mountains.
effected successfully by American engi: object of our profession is to consider neers only because they have appreciated and determine the most economic use another side of the problem presented of time, power, and matter." to them. A past president of the Am- That true economy, which finally seerican Society of Civil Engineers, a man cures in a completed work the best reof rare judgment and remarkable execu- sults from the investment of capital, in
first cost and continued maintenance, is an essential element in the consideration
of any really great engineering feat. Perspective View of St. Gothard Spiral Tunnels, in the Alps.
The difficulties involved in the con
struction of a tunnel, after the line and tive ability, the late Ashbel Welch, said, dimensions have been determined, dein discussing a great undertaking pro- pend generally upon the nature of the posed by an eminent Frenchman : "That material found as the work advances. is the best engineering, not which makes Solid rock presents really the fewest the most splendid, or even the most per- difficulties, but it is seldom that tunnels fect, work, but that which makes a work of considerable length occur without that answers the purpose well, at the
least meeting material which requires special cost.” And it may be remarked, as to provision for successful treatment. In the project which he was then discussing, that after a very large expenditure where the roof of the tunnel is to be,
some cases great portions of the rock, and an experience of eight years since
downward with enormous weight, that discussion, the plans of the work being detached from the adjacent mass have been modified and the identical
by the occurrence of natural seams. suggestions made by Mr. Welch of a This was the case at the tunnel excaradical economical change have been this vated for the West Shore Railroad near year adopted.* Another eminent Am- the bank of the Hudson River under erican engineer, whose practical experi- the Military Reservation of West Point. ence has been gained in the construction The time occupied and the cost of buildand engineering supervision of more than ing this tunnel were greatly increased five thousand miles of railway, said, in by this unexpected obstacle. his address as President of the American Society of Civil Engineers : “The high encountered, and the passage then is at
At other places soft material may be made to the substitution of locks in the tended great difficulty. Temporary Panama Canal for the original project of a canal at the
supports, generally of timber, and of
great strength, have often to be used at every foot of progress to prevent the material from forcing its way into the excavation already made. In long tunnels the ventilation is a difficult problem, although the use of com
pressed air drills has aided greatly in its solution.
Among the great tunnels which have been excavated the St. Gothard is the most remarkable. It is 94 miles long, with a section 26 feet wide by 19 feet high. The work on this tunnel was continuous, and it required 91 years for its completion.
The Mont Cenis tunnel, 8} miles in
length, was completed in 12 years. Plan of St. Gothard Spiral Tunnels.
The Hoosac Tunnel, 44 miles in length,
26 feet wide and 214 feet high, was not prosecuted continuously; it was completed in 1876.
These tunnels are notable chiefly on account of their great length; there are others of more moderate extent
which have peculiar features ;
curve would give;
at the side; still descending, it enters the mountain at another point and continues in another circular tunnel until it finally emerges again, under itself, but at a comparatively short horizontal distance from its first entry, having gained the required descent by a continued grade through the tunnels. The profile above shows the descent, upon a greatly reduced scale, the heavy lines marking where the line is in the tunnel.
Profile of the Same.
The remarkable success achieved by engineers in
Bridge Pier Founded on
securing suitable foundations at great expedient is the use of piles, which are depths is, of course, hardly known to driven into the ground, often to a very the thousands who constantly see the considerable depth, and sustain the load
placed upon them by the friction upon the sides of the piles of the material in which they are driven. It is seldom that dependence is placed upon the load being transferred from the top to the point of the pile, even though the point may have penetrated to a comparatively solid material. Wood is generally used for piles, and where the ground is permanently saturated there seems to be hardly any
known limit to their duraFoundation Crib of the Poughkeepsie Bridge.
bility. The substructure of
foundations generally, where structures supported on those founda- it is certain that they will always be in tions, but in any fair consideration of contact with water, can be, and gensuch engineering achievements this must erally is, of wood, and the permanency not be omitted. The beautiful bridge of such foundations is well established. built by Captain Eads over the Missis- An exception to this, however, occurs in sippi River at St. Louis, bold in its de- salt-water, particularly in warmer counsign and excellent in its execution, is an tries, where the ravages of the minute object of admiration to all who visit it, Teredo Navalis and of the still more but the impression of its importance minute Limnoria Terebrans destroy the would be greatly magnified if the part wood in a very short period of time. below the surface of the water, which These insects, however, do not work bears the massive towers, and which ex- below the ground-line or bed of the tends to a depth twice as great as the height of the pier above the water, could be visible.
The simplest and most effective foundation is, of course, on solid rock. In many localities reliable foundations are built upon earth, when it exists at a suitable depth and of such a character as properly to sustain the weight. Foundations under water, when rock or good material occurs at moderate
60 Feet. depth, are constructed frequently by means of the coffer-dam, which is simply an enclosure water. In many special cases hollow made water-tight and properly connect- iron piles are used successfully : ed with the bottom of the stream. The The ordinary method of forcing a pile water is then pumped out and the foun- into the ground is by repeated blows dation and masonry built within this tem- of a hammer of moderate weight; betporary dam. W1 th naterial is not of ter success being obtained by frequent a character to sustain the weight, the next blows of the hammer, lifted to a slight