352
DOCK ENGINEERING.
Fig. 325.
to all classes of caisson. Swinging caissons are not numerous. One is
chosen for illustration from the entrance to a graving dock, leading out of
the Victoria Dock at Dundee (fig. 325). In plan, its only distinguishing
feature from a caisson of the ordinary rectangular type is the hinge about
which it turns, which is situated at the apex
of a triangular arm. One side of the arm
forms a continuation of the outer face of the
caisson, so that the latter can be swung well
clear of the entrance. The entrance itself is
splayed in order to admit of this arrange-
ment. When in the closed position, the
caisson is suspended from corbels in the
masonry at each side, and the process of
opening consists in floating it off these sup-
ports, by pumping air into a pneumatic
chamber. The reverse operation of allowing
the compressed air to escape causes the caisson to settle upon its bearings.
Figs. 326 to 329 exhibit the construction of the caisson in detail.
........................................ ,
ELEVATION. LONGITUDINAL SECTION.
SECTION.
Figs. 326, 327, 328, and 329. —Swinging Caisson at Dundee.
Traversing Caissons include all those whose motion is rectilinear. They
may be subdivided into sliding, rolling, and floating caissons, according to
the mode of travelling, but in each case they occupy a rectangular recess,