278
DOCK ENGINEERING.
side of the case. The poste were provided with grooves, into which panels
were slid, extending from post to post. The bottom and sides of the case
were lined with jute bagging, and tie-rods, passing through the posts and
from side to side, prevented the case from being burst open by the lateral
pressure of the fluid conerete. The heart of each post was a piece of Baltic
fir, 20 feet long by 12 inches by 6 inches, scantling; the pieces of wood for
forming the grooves were fixed to the larger sides. The panels were built
up of short pieces of plank 2 feet long, placed vertically, so as to form a
slab 7 feet 9 inches by 2 feet by 3 inches, and they were backed by two
horizontal planks 7 feet 4 inches by 11 inches by 3 inches. The ends
of these formed the tongues which slid in the grooves in the sides of the
posts. The tie-rods were of wrought iron | inch diameter, in convenient
lengths, connected by f-inch shackles. The jute bagging was 39 inches
wide and weighed 29| ozs.; it cost 8d. per lineal yard and could generally
be used twice. The proportions of the conerete found best for the work
were 1 cement to 3 sand and 4 gravel; much of it was executed, however,
in the proportion of 1 cement to 4 sand and 5 gravel.
CROSS SECTION
PLAN METAL FRAMEWORK
Figs. 207, 208, 209, and 210. —Caisson at Zeebrugge.
A spécial adaptation of the concrete block system, as practised in the
construction of the outermost portion of a mole at Zeebrugge, merits some
notice. It consisted in the formation of hollow blocks of concrete of height
sufficient to reach above low water from the ground level. These were
floated out into position, sunk, and filled with concrete. The circumstances
at Zeebrugge were favourable to this method, the depth of water not
exceeding 30 feet at low water and being generally 26 feet.
The blocks, or caissons (figs. 207 to 210), were moulded about an iron
frame with plated sides, and were 80 feet long by 30 feet wide by 30 feet deep.
This gives a volume of 72,000 cubic feet each, and a total weight of about