120
Molesworth’s pocket-book
Hydraulic Piles.
bottom length.
These piles were sunk for a railway viaduct over the sands
In Morecambe Bay. Spans, 30 feet; two main and two raking
piles per pier; rake of piles, 1 in 12. Piles in lengths of
9 feet, 10 inches diameter outside; metal f thick. Diameter
of discs of main pile, 30 inches; ditto of raking pile, 18 Inches.
Sustaining power of sand, about 5 tons per square foot.
Average depth sunk below surface of sand, 20 feet; ditto at
opening spans, 26 feet; piles defended from scour by a weir
of rubble stone.
Orifice at disc, for discharge of water, 2 inches diameter.
MODS OF SINKING.
The piles were sunk from pontoons, each pontoon being
filled with a pile engine and a donkey engine about 2 horse-
power. Mr. Brunlees recommends for future operations the
fitting of the pontoons with sufficient appliances for sinking
all the piles of a pier simultaneously. The piles are lashed
to the block of the pile engine, which acts as a guide; there
is another guide low down on the pontoon; the pile hangs
with a loose chain, so that its weight assists in the sinking.
When attachment is made with a flexible hose to the donkey
engine, and the water pumped in issuing at, the orifice washes
away the sand in the marly deposit, an alternating rotatory
motion is given, by which the cutters cast on the disc loosen
the marl and allow it to be washed away. Piles are drawn
by pumping and lifting the pile by means of the pile engine.
Two piles generally fixed during an ebb tide.