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i86
HARBOUR ENGINEERING.
5 tons when submerged. They were fitted with the electric light and
telephonic communication, but it is recorded that the men preferred
mechanical signals.
The foundations generally were carried from 4 feet to 6 feet into the
chalk and flint bed, and were protected from the abrading action of sea
currents on the outer face by an apron of concrete blocks 25 feet in width.
Excavation for foundation work was carried out by grab-dredging down to
within 12 inches of the finished level, and the remaining material removed by
the aid of bell-divers. Four men were engaged in the bell, excavating and
finishing the foundation ready to receive the lowermost course of blocks.
Each shift was of three hours' ’duration, and two shifts per diem were generally
worked by the men. When the weather was favourable, work was con-
tinuons, night and day.
The greatest depth of the foundations is 53 feet below L.W.O.S.T., the
average depth being 47 feet. There was thus an average working head of
66 feet at H.W.O.S.T., corresponding to a pressure of 29 Ibs. This head has
been found to be a maximum for working under comfortable conditions; on
several occasions, when the depth was exceeded for a short period, incon-
venience was experienced from the extra pressure.
Very excellent plant was provided by the contractors for the préparation
of the concrete blocks. In the workyards six electric portable concrete
mixers were used, each capable of turning out about 100 cubic yards of
concrete a day. The mixers were of the Messent type, revolved by a motor
of 18 H.-P., and driven from the point where the aggregate was received to
the block moulds where the finished concrete was deposited, by a 25 H.-P.
motor. The gauge of the mixers was 11 feet 7 inches.