Screw-pile.
A pile having a screw-thread at its lower end to enable it more readily to penetrate hard ground and to hold it firmly in position.
Screw-piles of small diameter are usually made of wrought-iron and solid; those of larger size are frequently hollow and made of cast-iron.
They were invented by
Mitchell, in
England, and are principally employed as foundations for lighthouses, for beacons, and for mooring buoys.
They were used in the foundations of the
Maplin Sand Lighthouse at the mouth of the
Thames, and the
Fleetwood Lighthouse, at
Fleetwood, in
Lancashire, both erected A. D. 1840.
a a a, mooring-pile.
b b, mode of sinking the piles into position.
c c, piles for signal, mile, or telegraph posts.
d d, piles for tethering animals, or, on a larger scale, for attaching guys or
crab moorings.
Fig. 4738 is a view of the screw-pile lighthouse on Thimble Shoal, near the entrance to
Hampton Roads.
This was designed by
Major Peter C. Hains, to replace the light-vessel on Willoughby Spit.
The shoal is of firm, hard compact sand, and the time employed in fixing the piles was rather less than two months. The light is of the fourth order.
A mooring-pile 3 feet 6 inches in diameter gives a resisting surface equal to 10 square feet, double that of a large anchor.
They are also more deeply imbedded than the latter, and thus acquire additional resistance.
They are screwed into the ground by vertical rods, and a lever above operated by men on barges.
A chain or buoy is attached to it.
The shafts of the cast-iron screw-piles used in the piers of bridges in the
East Indies were cylinders 1 inch thick, 30 inches in external diameter, and in lengths of 9 feet. They were connected by internal flanges and bolts.
The lowest section formed
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the screw of the pile, having a thread 54 inches in diameter.
The cylinders were eventually filled with concrete.
These piles were screwed into the ground by means of 4 levers, each 40 feet long, and having 8 bullocks yoked to it. They penetrated from 20 to 45 feet.
