The Viaduct Works' Handbook

54 The cost of cast-iron piles is not materially affected by the diameter adopted; but with wrought-iron solid piles the cost in- creases very much with the diameter, whether the bars be produced by the rolls, or formed, as the larger sizes are, under the steam hammer, the difficulty of producing them from the rolls increasing with their weight. The cost of cast-iron screw piles may be approximately calculated at per foot run from the following:— s. d. Piles 10 inches diameter, 3 inch thick, per foot run 7 6 Ditto 12 ditto 1 ditto ditto 10 11 Ditto 15 ditto 1 ditto ditto 14 2 Ditto 18 ditto 1 ditto ditto 17 5 Wrought-iron screw piles would be, approximately, as follows :— 20 feet. 30 feet. 40 feet. £s. d. £ 8. d. £ 8. d. 4 inches diameter, per length 6 0 0 8 8 0 13 13 0 each 5 ditto ditto 9 10 0 13 10 0 20 17 6 „ 6 ditto ditto 15 17 6 22 10 0 83 0 0 „ 7 ditto ditto 25 10 0 41 10 0 51 15 0 „ PIERS OR JETTIES AND LANDING-STAGES. The following illustrations of a screw-pile jetty, 300 feet long, 33 feet wide, manufactured at Crumlin, may serve as a useful example on the wrought-iron “ Mitchell ” screw principle. It is supported upon 60 piles of solid iron, 4 inches diameter, arranged in the form of fixed trestles, and placed 15 feet apart; the screws are of cast-iron, 3 feet diameter; each screw is carefully fitted to its wrought-iron shaft, and secured thereto by a turned steel pin passing horizontally through a corresponding hole drilled through the boss of screw and end of pile shaft; each pile extends about 12 feet into the ground, and the part above ground varies in height according to the slope of the surface, from 19 feet to 25 feet; the top of each trestle is surmounted by a fight iron latticed girder, 33 feet long; the height from high-water mark to level of platform is 5 feet. The platform consists of timber, and is composed of longitudinal joists, 12 inches by 9 inches, placed about 3 feet 9 inches apart, centre to