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Road, represented in Plate I. Fig. 6., and the Fidlor Burn Bridge, on the Lanark Road, represented in Plate I. Fig. 7.*
The suspension bridge over the Menai Straits, in North Wales, is of a similar character, for, besides its use in passing these straits, it has improved the road by its being no longer necessary to descend to the level of the water. See Plate I. Fig. 8.
In most cases, however, valleys may be crossed by high embankments of earth, such as the chalk hill embankment near Dunstable, and that near Chirk, in North Wales.
In some situations it may be advisable to pass through a hill by means of a tunnel, instead of by deep cutting.
There are three works of this kind on the Simplon Road. One of them, “la grande galerie de Gondo,” is 240 yards in length, 8. in breadth, and the same in height. † There is a similar work at Puzzuoli, near Naples, which is nearly half a league long; it is fifteen feet broad and as many high.
* To this list may be added the Dean Bridge over the Water of Leith at Edinburgh, which is above 100 feet high, and consists of four arches of 90 feet span; and a bridge at Pathhead, on the Coldstream road of five arches of 80 feet span.
† It would appear from the following extract from a Memoir of M. Ceard, on the Simplon Road, that some great errors were made in laying out the line of this famous road.
M. Ceard was the chief engineer, and claims the merit of being the author of the plan.
Troop of M. CThe plan of the road, once adopted, it became the duty of the head engineers, and more especially of the younger officers under their command, strictly to follow what had been decided upon.
Cand the engineer with whom he acted, entertained, however, a different opi. nion, and exercised their discretion. After much labour was uselessly expended by them in attempts which they were obliged to abandon, the first ascent, which should have been an uniform inclined plane, rising regularly six inches in seventy-two, on the side of the mountain of Brandevald, was constructed in an irregular manner, the incline rising sometimes seven inches in seventy-two, sometimes eight, sometimes three, or less, and sometimes nothing. This error was committed in my absence, and when I discovered it, too much labour and money were expended, to abandon what had been executed, without considerable loss; besides which, the government would have been exposed to the public ridicule, which would be excited by the exposure of the blunders of those employed by it. Such was the first consequence of M. C-'s mismanagement in this ascent.
The second division of the road was arranged to proceed from the first summit to the bottom of the valley of Ganther. This was to have been effected by an inclined plane, at the rate of two inches in seventy-two; but the course followed by these engineers doubled this rate ; and if I had not interrupted their departure from the original plan, the road would
The peculiar circumstances of a river may render it necessary to deviate from a direct line in laying out a road.
have been carried across three torrents, over which bridges must have been thrown, in situations almost inaccessible, and exposed to destruction by avalanches, instead of a single bridge, which alone was necessary by the original plan, situated also in a position free from those objections.
The consequences of this second error in arranging the inclinations of the road were, that it was necessary to elevate the line of the road, (in order to avoid the inconvenience of having to make a descent and then an ascent,) and to give double the necessary height to the bridge of Ganther, the position of which admitted of no change. It was necessary
also to increase the height of the stone buttresses of the bridge, to the extent of at least twenty metres (sixty-five feet), to supply the place of the support which would otherwise have been derived from natural rocks; and finally, to construct considerable causeways, and to make the carpentry of the bridge of that height which the torrent required. Such were the consequences of M. C—'s proceedings.
I shall continue to investigate the labours of this young engineer.
Having to superintend, besides the Simplon road, fifty leagues of road in Italy, in the Valais, in Savoy, and upon Mount Jura, I could not be always present at the Simplon to watch the proceedings of these gentlemen ; but I trusted that the superintending engineer, C-, satisfied with the consequences of his first departure from the plan laid down by the council, would follow, for the future, implicitly the A difficulty may arise from the breadth of the river requiring a bridge of extraordinary dimensions, or from the land for a considerable distance on the sides of the river being subject to be covered with water to the depth of several feet in floods.
directions given to him. I was, however, deceived in this expectation.
The plan prescribed by the council did not permit, in the ascent from the bridge of Ganther to the summit of the Simplon, any inclination exceeding five inches in seventytwo. M.C—, however, caused to be constructed three pieces of road, in a zig-zag form, which, while they increased the length of the road to the extent of 2169 yards, far from moderating its acclivity, occasionally increased it, a serious error in works of this nature. He acted in this case on his own responsibility ; relying, perhaps, on that of his chief of brigade. As a consequence, it became necessary to mount and traverse some difficult ground, to form enormous excavations, worse than useless, because dangerous from the snow which would collect in them, a circumstance most to be avoided, and to carry the level of the road under the glaciers; all
consequences of the original error committed at the base, in having ascended too rapidly, instead of having ascended by one regular inclined plane, rising five inches in seventytwo, as had been decided on in the original plan, and thus reaching the summit of the Simplon and the Hospice, by the course at once the most gentle in its ascent, and the noblest in its length. This piece of work, on which about 300,000 francs had been squandered, is likewise due to M.C-, who in two leagues and a half of road has committed, as we have seen, several serious blunders, in spite of all my efforts to oppose him.
In these cases it may appear, upon accurately calculating and balancing the relative inconvenience and expense of endeavouring to keep a straight line and of taking a circuitous route, that upon principles of security, convenience, and expense, the circuitous course will be the best.
In general, rivers have been allowed to divert the direct line of a road too readily. There has been too much timidity about incurring the expense of new bridges, and about making embankments over flat land to raise the roads above the level of high floods.
These apprehensions would frequently be laid aside, if proper opinions were formed of the advantages that arise from making roads in the first instance, in the shortest directions, and in the most perfect manner. If a mile, half a mile, or even a quarter of a mile of road be saved, by expending even several thousand pounds, the good done extends to posterity, and the saving that will be the result in annual repairs and horse labour, will, before long, pay off the original cost of the improvement.
BOGS AND MARSH GROUND.
The elastic nature of all bogs and marshes, and of all boggy and bottom land, makes it im