The Viaduct Works' Handbook

so The cost of sinking and fixing cylinder bridge piers in England may be approximately reckoned as follows. These prices will of course vary with circumstances peculiar to the country or locality, or price of labour. Taking cylinders 6 feet diameter as the basis, a cylinder of this size may be sunk to a depth of 20 feet below water- line by the use of scoops alone for about 30s. per foot down; beyond this depth the scoops become inconveniently long for use, but the process of sinking may be continued, circumstances being favourable, by divers, from 20 to 60 feet, for about 60s. per foot down; and below that depth, from 60 to 90 feet, still by divers and scoops, for about 80s. per foot down. Where the ground contains boulders or hard strata the com- pressed air apparatus is used, and the cost may be taken at £4 per foot down to 60 feet below water-line, and from 60 feet down to 90 feet at £6 per foot down. If the strata is loose sand and gravel full of water, the sinking can be done by Kennard’s patent sand pump, (particulars of this machine are given in another part of this book,) and the cost may be reckoned by this process to be 30s. per foot down, and may be carried to almost unlimited depth without increase of cost. The above prices include building up, and weighting and removing weights where necessary. Upon the same principle, and with the same object (avoiding the construction of the ordinary coffer-dam), cylindrical and rectangular caissons are employed for foundations of abutments. The opposite engraving represents an example of screw pile piers, used in a railway bridge lately made at these works, which is erected in this country over an arm of the sea, where the water is 23 feet at high water and 3 feet at low water. The bridge is nearly a mile in length, consisting of spans of 30 feet each. It is made sufficiently strong for a double line of railway. The piles are arranged in a single row, as shown in sketch, and are 12 inches diameter, and are of cast metal, in 10-feet lengths, J of an inch thick, turned at ends, jointed with flanges containing 8 bolts, 1 inch diameter, in each joint. The lower lengths are made 17 feet each, and cast with screws 2 feet 10 inches diameter, and the metal at bottom is 1g inches thick; they are braced together with angle iron horizontally and flat bars diagonally. It may be mentioned that in some cases where a very