terstices between the blocks with concrete, a continuous masonry
wall faced with ashlar was built on the top out of water. A quay wall
was built up to a little above low water on a similar principle at
Cork, with three smaller blocks as a foundation, in lengths of 8 ft.
Cylindrical well foundations have been extensively used for the
foundations of the quay walls along the Clyde, formerly made of brick,
but subsequently of concrete, sunk through a considerable variety of
alluvial strata, but mostly sand and gravel fully charged with water.
Compressed air in bottomless caissons has been increasingly employed
in recent years for carrying down the subaqueous foundations of river
quay walls, through alluvial deposits, to a solid stratum. About 1880,
a long line of river quays was commenced in front of Antwerp,
extending in the central portion a considerable distance out into the
Scheldt, with the object of regulating the width of the river
simultaneously with the provision of deep quays for sea-going vessels;
and the quay wall was erected, out of water, on the flat tops of a
series of wrought-iron caissons, 82 ft. long and 29-1/2 ft. wide,
constructed on shore, floated out one by one to their site in the
river between two barges, and gradually lowered as the wall was built
up inside a plate-iron enclosure round the roof of the caisson, which
was eventually sunk by aid of compressed air through the bed of the
river to a compact stratum (fig. 14). The weight of the wall
counteracted the tendency of the caisson and the enclosure above it to
float; and the caisson, furnished with seven circular wrought-iron
shafts, provided with air-locks at the top for the admission of men
and materials and for the removal of the excavations, was gradually
carried down by excavating inside the working chamber at the bottom,
6-1/4 ft. high, till a good foundation was reached. The working chamber
was then filled with concrete through some of the shafts, the
plate-iron sides of the upper enclosure were removed to be used for
another length of wall, the shafts were drawn out and the hollows left
by them filled with concrete, the apertures between adjacent lengths
were closed at each face with wooden panels and filled with concrete,
and a continuous quay wall was completed above. The most recent quay
walls constructed in the old harbour at Genoa were founded under
water on a rubble