Page:Popular Science Monthly Volume 89.djvu/551

 Holding the Hudson at Bay

���When the project is completed New York will have piers large enough to enable the world's largest ocean-liners to dock in a few minutes instead of several hours

��TO make wa\' for the giant steam- ship piers which when finished will enable the world's largest ocean- liners to dock within a few minutes, instead of a few hours, which is now the case, the Citj' of New York, through its Department of Docks and Ferries has constructed a cofferdam which holds sixty-eight feet of the Hudson Ri\L'r at bay while workmen are clearing out rock from the river-bottom and laying the shore-ends of the piers.

The engineering world was much interested in the raising of the battleship Maine in Havana Harbor, where a head of water thirty-seven feet deep had to be reckoned with, but interest has now shifted to New York. At Havana the cofferdam was elliptical and the rounded ends helped to reinforce the sides. In New York the wall holding back the waters is L-shaped, eight hundred feet long on one side and three hundred feet on the other.

Interlocking sheet steel-piling was used to form the backbone of the coffer- dam, and this was dri\en so as to make a succession of contiguous pockets ap-

��proximately sixteen feet in width and twenty-four feet in length. These pockets were filled with material dredged from the river-bottom, and as it settled it turned the pockets into steel-clad pillars of earth. The steel piles were driven down to the underlying bed-rock which dipped riverward. But this was not a sufficient guaranty of rigidness. The object of shutting out the ri\-cr was to- enable hundreds^ of workmen, with pneumatic drills, to get at the rock normally below the tide so that it could be blasted away smoothly, and structural work reared upon the resultant clean ledge. This structural work is eventually to support long piers for the accommoda- tion of liners one thousand feet in length. To guard against any possible collapse it was decided to build a slanting rip-rap bank inside the cofferdam, and stone was piled up until the base of the dam had a width of seventy feet. But there was a point where this rip-rap could not be built; it was at the corner where the inshore end of the cofferdam joined the main bod\' of the bulkhead. There the engineers had to have the rock uncovered

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