28o
DOCK ENGINEERING.
though in some cases, pockets of earthwork have been employed. With
either system of construction, it is essential for the stability of the work
that the opposite facings should be securely tied together by well bonded
cross walls, or by horizontal lacing courses at regular intervals. The
largest possible stones should be chosen for the outer blocks, and they
should be secured to one another by dowels and plugs as well as dovetailed
Fig. 212. —Pier at Havre.
into the hearting by an efficient system of bonding. The south pier at
Havre (fig. 212) is a typical example of masonry construction. It has
inclined ashlar facings, averaging 5 feet in thickness, connected, at intervals
of 5 feet in height, by lacing courses, 2 feet thick. The bottom width is
Fig. 213. —Jetty at
Dover.
36 leet 6 inches, and the top width, between parapet
walls, 18 feet 6 inches. The pavement is 7 feet 6 inches
above high water of equinoctial tides, and 33 feet
4 inches above ground level.
A combination of a granite ashlar facing with a
hearting of concrete blocks is exemplified in a pier
at Dover, constructed about the year 1855. Present
practice at that port favours the concrete block system
throughout, with a thin facing of granite rubble above
low-water level (fig. 213).
Piers wholly of loose rubble are indistinguishable
from breakwaters, their principal function being the
destruction of waves. There are but few instances of such works being
used for landing purposes. There is one, however, at Kingstown Harbour,
near Dublin, where a long inclined mound of loose rubble, with slopes
ranging from 1 to 1 to 5 to 1, is crowned with a pitched surface on the
inner side, 38 feet in width. The maintenance of such disorganised masses
is apt to be costly, as they suffer considerably from the effects of wave
action.