•case, it consisted of fine clean
sand filling, carefully watered
and rarnmed in thin layers.
The foundations of a neigh-
bouring lock rest directly upon
a very thick bed of fine sand
which underlies the district, and
a similar mode of foundation
was contemplated in the first
instance for the new lock. But
the work also occupies a portion
■of the site of the old sluicing
basin, and, on examination, it
was found that very extensive
excavation had resulted from
water scour in front of the
sluice gates, and that the sand
bed had been disturbed to a
considerable depth. Conse-
quently, as it was desirable
that so important an under-
taking should rest upon a
homogeneous base, it was de-
cided to carry out a general
scheme of close piling.
The piles employed were of
oak, of 10 inches mean dia.
meter, 14 feet 9 inches long
under the floor of chamber,
16 feet 3 inches long under the
sills, and 18 feet long under the
aprons. The piles were pitched
at distances proportionate to
the thickness of the masonry,
which attains 62 feet in the
side walls of the pierheads and
is reduced to 13 feet within
the chamber. The number of
piles was 6,300, and they were
driven by ten steam - piling
machines and three ringing
machines.
The floor, which varies in
thickness from 13 to 18 feet, is
formed by a layer of brick work,
186. —Dam at Dunkirk.