The Viaduct Works' Handbook

at a third less than masonry, as may be seen from the following estimates:— COST OF AN IRON PIER. £ S. 163 tons castings, at £13 .2110 0 7 tons wrought-iron, at £‘16 112 0 1128 yards excavation, at 1s. Cd. 84 12 1400 cube feet Ashlar masonry, at 3s...........................210 0 42 yards concrete, at 8s. . 16 6 £2541 18 COST OF A MASONRY PIER. £ S. d. 2197 yards excavation, at 1s.6d. . . . 164 15 6 1041 yards masonry foot- ings, at £15s. . 1301 5 0 2120 yards, at £1 5s. . 2650 0 0 £4110 0 6 The difference in favour of iron pier, £1574 2s. 6d. The cost of erecting, in England, structures of this kind varies from £2 to £4 per ton. The piers of Tagus Bridge, the superstructure of which has been already described, at page 12, with illustrations, are an example of the larger cylindrical piles ; in this bridge fifteen piers were required, the average height of each pier 50 feet above the bed of the river— a detail sketch is given at opposite page. Each pier is formed of three cast-iron cylinders, 6 feet in diameter, 1 inch thick, made in lengths of 6 feet, each length being built up of 4 plates or segments, planed and turned at their junctions, so that when bolted together with li-in. diameter bolts, and caulked with a little red lead, the joints are made air-tight. The weight of these piers averages 25 cwt. per foot run. The weight of bracings and bolts about 2 cwt. per foot run. Estimating the price of the cast-iron at £8 per ton, and wrought-iron at £16 per ton, f. o. b. an English port, it gives the price of such a pier at £11 12s. per foot run. The foundations of these piers, or that portion which is sunk below the bed of the river, to an average depth of 36 feet, are constructed by prolonging the outer piles 6 feet diameter to the requisite depth, while the central piles, which carry a greater weight, are increased to 8 feet diameter, to give the requisite area of bearing ‘ surface; they were sunk in the following manner :— A sufficient number of 6-feet lengths, to reach a convenient distance through the water, are bolted together (with thick paint at the joints, to make them tight), and thus lowered from a raft or temporary stage into the position required; the earth is then removed from inside by scoops or spoons, furnished with long