Engineering Wonders of the World
Volume I

THE ST. LOUIS BRIDGE. 167 to the passing steamers. Two floods sufficed to remove every vestige of the island, leaving the wreck of the America uncovered by sand and 40 feet below water mark, where, in 1856, the property was recovered. Pilots are still navigating the river who saw this wreck lying near the Arkansas shore, with her main deck scarcely below low-water mark at the time she was lost. When the wreck was recovered the main channel of the Mississippi was over it, and the hull had been let down by the action of the current at the bottom nearly 40 feet below the level at which it first rested ; and the shore had receded from it by the abrasion of the stream nearly half a mile.” The coffer-dam used at the west abutment consisted of outer and inner jackets of close- fitting iron sheet piles, with the space between the two packed and rendered Troubles and , ,. , , 7 r , water-tight with clay. Before Obstacles. , each separate sheet was sunk a path had to be cut for it with a chisel-edged iron pile, driven by steam. The obstacles this chisel had to deal with comprised oak timbers four inches thick, paddle wheels, iron plates and furnace bars, and a heavy engine crank; and even when the dam was regarded as complete, it was found that large sections of the wrecks had been enclosed within the space or built into the walls. The pressure and necessary removal of these foreign bodies caused fre- quent flooding and considerable consequent delay in the operations. The difficulties at the west abutment have deserved notice from the curious mischance that gave rise to them ; but the next section of the work to be undertaken, the sinking of the east pier, was in the highest degree criti- cal. It would appear that suc- cess or failure here was, in general opinion, to decide the fortunes of the whole bridge, and the engineers were well advised in proceeding promptly to settle the doubts of the capital- ists. Exploration borings had found bed- rock in this part of the channel at the great depth of 117 feet below the “city direc- trix ” or standard of high water, from which Pneumatic Caissons adopted. CLOSING THE ARCHES. (From a Sketch by Howard Penton.)