icipated, as in excavating for the
foundations, these holes might give rise to the outflow, under
pressure, of underlying quicksand into the foundations. As docks are
generally formed near rivers or estuaries, these strata are commonly
alluvial; but being situated at some depth below the surface, they are
usually fairly hard. When they consist of gravel, clay or firm sand,
the walls can be founded on the natural bottom excavated a few feet
below the bottom of the dock, their weight being somewhat distributed
by making them rest on a broad bed of concrete filling up the
excavation at the bottom. When, however, fine sand or silt charged
with water, or quicksand is met with at the required depth, the
necessary pumping and excavation for the foundations might occasion
the influx of sand or silt with the water into the excavations,
leading to settlement and slips; or the soft stratum might be too
thick to remove. The wall may then be founded on bearing piles driven
down to a solid stratum, and having their tops joined together by
walings and planking, or by a layer of concrete, upon which the wall
is built. Or the soft stratum can be enclosed with a double row of
sheet piling along the front and back of the line of wall, by which it
sometimes becomes sufficiently confined and consolidated to sustain
the weight of the wall on a broad foundation of concrete; or it can be
excavated without any danger of sand or silt running in from outside;
whilst the sheet piling at the back relieves the wall to some extent
from the pressure of the earth behind it, and in front retains the
wall from sliding forwards. Firmer foundations have been obtained by
sinking brick, concrete or masonry wells through soft ground to a
solid stratum, upon which the dock wall is built. Clusters of small
concrete cylinders, in sets of three in front, and a line of double
cylinders at the back, were used for the foundations of the walls of
Prince's dock at Glasgow. Wells of rubble masonry were sunk in the
silty foreshore of the Seine estuary for the walls of the Bellot docks
at Havre; and they served as piers, connected by arches, for the
foundations of a continuous dock wall above, being carried down to a
considerable depth through alluvium at the St Nazaire, Bordeaux and
Rochefort docks. These well foundations, derived from the old Indian
system, are built up upon a curb, sometimes furnished