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PILING.
79
mud against their sides to support both themselves and the load tliey cariy.
And although, under ciroumstances of this kind, great sustaining power could
hardly be expected, it is recorded that loads equivalent to 40 tons per pile
have been safely carried. This figure, indeed, is very much in excess of the
limit previously specified. At one-tenth of a ton per square incli a circulai
pile, 18 inches diameter in the butt (such as is commonly used at New York),
would only support 24 tons and a 22-inch pile not more than 36 tons.
Mr J. A. Bensel, engineer-in-chief of the Department of Docks and Ferries
at New York, has carried out some experiments on the limiting capabilities of
the piles employed there.1 A platform was built near the foot of Seventeenth
Street, North Kiver, and the piles to be tested, all about 80 feet long, were
driven in four groups within the area of the platform, and arranged as
Fie. 72.—Plan of Piled Platform of Quay Wall, New York Harbour;
follows :— Group I., plain, unlagged piles. Group II., piles lagged with four
pieces of 5-inch by 6-inch lumber, 30 feet long. Group III., piles lagged
as in Group II., but arranged in pairs, so as to obtain the effect of greater
proximity, the piles in each pair being spaced 2 feet 8 inches apart. Group
IV., piles lagged with two pieces of 5-inch by 6-inch lumber, and two pieces
of 4-inch by 10-inch lumber, in lengths of 30 feet, this with the object of
obtaining results for a different style of lagging.
The testing platforms were loaded with granite and concrete blocks
eighteen davs after the last pile had been driven, thus affording the mud an
opportunity of consolidating round the piles. A boring, taken at the site of
the platform, indicated mud of uniform character to a depth of 100 feet below
mean low water-line. The consistency of the mud at the top was such as to
admit of the piles sinking by their own weight through 10 or 15 feet when
lowered graduallyj a little further down the mud attained the consistency
1 Bensel on Dock Work in New York Harbour, Proc. Int. Eng. Cong. St Louis, 1904.