Engineering Wonders of the World
Volume I

THE GREAT VICTORIA BRIDGE. 207 To with- stand the enormous pressure of the ice, the bridge piers had to be ELEVATION OF PIER. mos^ solid con- struction. It was decided to build them up from the solid rock with stones weigh- ing from 5 to 20 tons apiece. The down- stream face of a pier was vertical ; the up- stream face carried a large sloping ice-breaker, sharp edged, of stones bonded with iron clamps. This gave the pier an outline roughly resembling that of a boot, up which the ice would climb until its own weight shattered it on the sharp angle of the breaker. At summer water-level twenty-two of the piers measured 90 feet by 18 feet; the other two, those for the central span, 90 feet by 28 feet. The employment of divers in an 8-mile current being impracticable, some plan had to excluding the water from the sites of the piers and abutments, and working on a dry bed. In a sluggish stream the forma- tion of cofferdams would have presented little difficulty ; here the reverse was the case. After careful de- liberation, the engineers decided to build in the quieter water near the banks the cais- sons needed to form the walls of a dam, tow them into position, sink them, and line them with an inner wall of puddled clay, rammed hard down in a puddle chamber so as to exclude all water when the pumps should be set to empty the dam. To prevent the cais- sons shifting when once sunk, they were pro- vided along the outside with steel piles, moving in grooves, which could be driven down into the bed of the river and so anchor the caisson. During the winter of 1854, as soon as the ice-bridge had formed, the contractors began be devised for Plan of Pier- building Operations. Marking out the Pier Sites. each pier was operations by marking out the positions of the piers on the ice, cutting holes, and taking soundings, while a road of a more or less level character was made, in the line of a bridge, over the rudely packed ice. The site for the centre of carefully marked by sinking an iron bar, 5 feet long and 4 inches in diameter, into the bed of the river, to serve as a guide for opera- tions in the spring following. This done, large cribs of woodwork and stone were sunk in position above the piers to act as anchorages while the dams were being floated into position. PLAN OF PIER AND REMOVABLE COFFERDAM INSIDE WHICH IT WAS CONSTRUCTED. The pointed end faces up-stream. The spring of 1854 opened early. On the 24th of May the first caisson to form part of the dam for the north abutment was towed up-stream and sunk, and in due course that part of the Work , j . . . commences, river-bed on which the masonry was to rise had been pumped dry. The first stone was laid at the end of August 1854, and before work ceased for the winter more than 85,000 cubic feet of stone had been set. Mean- while the approach embankment was built of stone faced with masonry on the up-stream side, and the dam for No. 1 pier—namely, that nearest the north abutment—was got into position and sunk. This pier was finished in November. Great trouble was experienced during the making of the dam for No. 2 pier, consequently for some of the other piers large cribs were used instead of caissons as barriers against the water.