CHAP. XX.] FOUNDATIONS AND CONSTRUCTION OF PIERS. 479

abutments contain about 6000 tons of masonry each, while those which support the great centre tube contain about 12,000 tons. The former are 15 feet wide, and the latter 18. Scarcely a block of stone used in the piers is less than seven tons in weight, while many of those opposed to the force of the breaking-up ice weigh fully ten tons.

As might naturally be expected, the getting in of the foundations of these enormous piers in so wide and rapid a river was attended with many difficulties. To give an idea of the waterpower of the St. Lawrence, it may be mentioned that when the river comes down in its greatest might, large stone boulders weighing upward of a ton are rolled along by the sheer force of the current. The depth of the river, however, was not so great as might be supposed, varying from only five to fifteen feet during summer, when the foundation-work was carried on.

The method first employed to get in the foundations was by means of dams, or caissons, which were constructed on shore, floated into position, and scuttled over the places at which the foundations were to be laid, thus at once forming a nucleus from which the dams could be constructed. The first of such dams was floated, got into position, scuttled, and sunk, and the piling fairly begun, on the 19th of June, 1854. By the 15th of the following month the sheet-piling and puddling was finished, when the pumping of the water out of the inclosed space by steampower was proceeded with, and in a few hours the bed of the river was laid almost dry, the toe of every pile being distinctly visible. By the 22d the first stone of the pier was laid, and on the 14th of August the masonry was above water-level.

The getting in of the foundations of the other piers was proceeded with in like manner, though frequently interrupted by storms, inundations, and collisions of timber-rafts, which occasionally carried away the moorings of the dams. Considerable difficulty was in some places experienced from the huge boulderstones lying in the bed of the river, to remove which sometimes cost the divers several months of hard labor. In getting in the foundations of the later piers, the method first employed of sinking the floating caissons in position was abandoned, and the dams were constructed of "crib-work,"* which was found more con*The dams of "crib-work" were formed by laying flattened pine logs along the

venient, and less liable to interruption by accident from collision or otherwise.

By the spring of 1857 a sufficient number of piers had been finished to enable the erection of the tubes to be proceeded with. The operations connected with this portion of the work were also of a novel character. Instead of floating the tubes between the piers and raising them into position by hydraulic power, as at Conway and Menai, which the rapid current of the St. Lawrence would not permit, the tubes were erected in situ on a staging prepared for the purpose, as shown in the following engraving. Floating scows, each 60 feet by 20, were moored in position,

whole outer edge of the work, and at intervals of from 5 to 10 feet parallel therewith throughout the whole of the breadth, connected with transverse timbers firmly treenailed and notched into them. When one course was formed, another was laid upon and firmly treenailed to it. After two or three courses were laid, transverse timbers were placed over them close together, so as to form a flooring, on which stone was placed to suit the crib as the work progressed. When the under side of the crib touched the bottom, it was carefully filled with loose stones and clay puddle to the water level. The process of puddling and pumping out the water, and building up the pier within the dam thus formed, then proceeded in the usual manner. In some cases a powerful steam dredge was employed to clear out the puddle-chambers.

CHAP. XX.]

BREAKING UP OF THE ICE.

481

and kept in their place by piles sliding in grooves. These piles, when firmly fixed in the bed of the river, were bolted to the sides of the scows, and the tops were leveled to receive the sills upon which the framing carrying the truss and platform was erected. Timbers were laid on the lower chords of the truss, forming a platform 24 feet wide, closely planked with deals. The upper chords carried rails, along which moved the "travelers" used in erecting the tubes. The plates forming the bottom of each tube having been accurately laid and riveted, and adjusted to level and centre by oak wedges, the erection of the sides was next proceeded with, extending outward from the centre on either side, this work being closely followed by the plating of the top. Each tube between the respective pairs of piers was in the first place erected separate and independent of its adjoining tubes; but after completion, the tubes were joined in pairs and firmly bolted to the masonry over which they were united, their outer ends being placed upon rollers so arranged on the adjoining piers that they might expand or contract according to variations of temperature.

The work continued to make satisfactory progress down to the spring of 1858, by which time fourteen out of the twentyfour piers were finished, together with the formidable abutments and approaches to the bridge. Considerable apprehensions were entertained as to the security of the piers and the unfinished parts of the work at the usual breaking-up of the ice. We take the following account from a letter written by Mr. Ross to Mr. Stephenson descriptive of the scene.

"On the 29th of March, the ice above Montreal began to show signs of weakness, but it was not until the 31st that a general movement became observable, which continued for an hour, when it suddenly stopped, and the water rose rapidly. On the following day, at noon, a grand movement commenced; the waters rose about four feet in two minutes, up to a level with many of the Montreal streets. The fields of ice at the same time were suddenly elevated to an incredible height; and so overwhelming were they in appearance, that crowds of the townspeople, who had assembled on the quay to watch the progress of the flood, ran for their lives. This movement lasted about twenty minutes, during which the jammed ice destroyed several portions of the quay wall, grinding the hardest blocks to atoms. The embanked approaches to the Victoria Bridge had tre

mendous forces to resist. In the full channel of the stream, the ice in its passage between the piers was broken up by the force of the blow immediately on its coming in contact with the cutwaters. Sometimes thick sheets of ice were seen to rise up and rear on end against the piers, but by the force of the current they were speedily made to roll over into the stream, and in a moment after were out of sight. For the two next days the river was still high, until on the 4th of April the waters seemed suddenly to give way, and by the following day the river was flowing clear and smooth as a millpond, nothing of winter remaining except the masses of bordage ice which were strewn along the shores of the stream. On examination of the piers of the bridge, it was found that they had admirably resisted the tremendous pressure; and though the timber "cribwork" erected to facilitate the placing of floating pontoons to form the dams was found considerably disturbed and in some places seriously damaged, the piers, with the exception of one or two heavy stone blocks, which were still unfinished, escaped uninjured. One block of many tons' weight was carried to a considerable distance, and must have been torn out of its place by sheer force, as several of the broken fragments were found left in the pier."

Toward the end of January, 1859, the plating of the bottom of the great central tube was begun. The execution of this part of the undertaking was of a very formidable and difficult character. The gangs of men employed upon it were required to work night and day, though the season was mid-winter, as it was of great importance to the navigation that the staging should be removed by the time that the ice broke up and the river became open. The night gangs were lighted at their work by wood-fires filling huge braziers, the bright glow of which illumined the vast snow-covered ice-field in the midst of which they worked at so lofty an elevation; and the sight as well as the sounds of the hammering and riveting, the puffing of the steam-engines, and the various operations thus carried on, presented a scene the like of which has rarely been witnessed. The work was not conducted without considerable risk to the men, arising from the intense cold. The temperature was often 20° below zero, and notwithstanding that they all worked in thick gloves, and that care was taken to protect every exposed part, many of them were severely frostbitten. Sometimes, when thick mist rose from the river, they would become covered with icicles, and be driven from their work.

CHAP. XX.]

ERECTION OF THE CENTRAL TUBE.

483

Notwithstanding these difficulties, the laying of the great central tube made steady progress. By the 17th of February the first pair of side-plates was erected; on the 28th, the bottom was riveted and completed; 180 feet of the sides was also in place,

and 100 feet of the top was plated; and on the 21st of March the whole of the plating was finished. A few days later the wedges were knocked away, and the tube hung suspended between the adjoining piers. On the 18th of May following the

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