I82
DOCK ENGINEERING.
faces become apparent. Oid walls are frequently to be found with considér-
able batter, both straight and curved, as in lig. 106, an old wall at Leith, and
fig. 107, a wall at Sheerness, constructed by the late Sir John Rennie. These
may be compared with the latest type of quay wall at Liverpool shown in
fig. 169.
A curved or splayed toe to a wall is a valuable feature, provided it be
not carried so high as to nullify the advantage of a vertical face. Prolonged
to some distance beyond the face line, the “toe” becomes an apron. The
former is illustrated in figs. 165 and 169, the latter in fig. 223. The object
of an apron is to prevent any abrading or softening action upon the ground
in front of the wall, whereby any forward movement would be assisted.
Fig. 108. —Wall at Kidderpur Docks, Calcutta.
Counterforts should be disposed, as far as possible, to form foundations
for the bases of columns of sheds, or other structures intended to be built
upon the quay. They can be carried up from any offset level. The inter-
vening spaces, instead of being occupied with filling, may in certain cases be
arched over, and the vaults thus formed left vacant in order to relieve the
pressure. Such arched counterforts are often arranged in two or more tiers.
Where circumstances render it desirable to still further lighten a wall,,
pockets may be introduced into its interior, either to be left empty or filled
with fight material. Fig. 108 shows the Kidderpur Dock wall treated in
this way, because of its weak foundation. Walls thus constructed, however.