2QO
DOCK ENGINEERING.
above the water line, an angle iron 6 inches by 5 inches by | inch, and the
lower, a channel iron 10 inches by 3 inches by J inch, connected in each
case by transverse through-bolts. The interior of the jetty is filled with
rubble. The top width is 14 feet, providing accommodation for a single
line of rails.
Figs. 229 and 230.—Jetty at Touapsé.
Composite Systems. —Perhaps the most remarkable development of
recent years is the intimate combination of iron and concrete for building
purposes, and not the least important application of the method is in
reference to piling. The earlier open-work systems, whether of iron or
wood, are subject to deterioration and decay—in the first case from
corrosion, and in the second from the ravages of sea worms. Hence a
combination of two materials, in which the durability of the one acts as
a preservative to the strength of the other, is an undoubted advantage.
Such is the principle of several well-known systems, in all of which iron
rods and bars are completely imbedded in concrete, so as to be beyond the
reach of external destructive agencies. Two of these systems, from their
primary application to building construction, are more fully described in
the chapter on Sheds and Warehouses. Here we are only concerned with
their adaptability to jetties and piers.
The Monier system, consisting of a mesh of metal wire incorporated in a
slab of concrete, has been used as an external cover for timber piles, and
also, in the form of cylinders, for bridge foundations. Monier tubes, in 3 feet
6 inch lengths, 21 inches internal diameter, If inch thick, with a hearting
of steel wire netting, 1| inch mesh, No. 16 gauge wire, have been used by
Mr. De Burgh for the protection of ironbark piles in Australia. In a
second instance, the cylinders were 3 feet 6 inches in diameter, with a
thickness of 2| inches. Both applications were successful, and indicate the
possibility of utilising Monier tubes on a more extended scale for marine
foundation work.