A Treatise On The Principles And Practice Of Dock Engineering

298 DOCK ENGINEERING. length of 2,800 feet. For 2,340 feet of this length, the width at the top is 35 feet, while for the remaining portion, the width is 41 feet. The width at the bottom varies with the depth, and is generally 120 feet at a depth of 40 feet below low water. The top of the pier is 10 feet above high water. A subway, 6] feet high by 4 feet wide, runs the entire length of the pier, and afiords access to the lighthouse in stormy weather. The shoreward portion of this pier, for a length of 385 feet, is constructed of conerete en manse, faced with granite blocks ; for the remainder of the pier, the super- structure is formed of granite-faced conerete blocks, varying in weight from 43 to 54 tons, set in lengths of 42 feet 7 inches each, by a radial hydraulic block-setting crane, which could set a 60-ton block GO feet in advance of its leading wheel. The interior of each length is filled with conerete blocks and mass conerete. Ihe superstructure is set on a foundation levelled to 21 feet above low water. This foundation was formed of 56-ton and 116-ton bags of 4 to 1 conerete deposited in a plastic condition on the rock. The conerete was enclosed in bags of jute sacking, weighing 27 ounces per yard, 30 inches wide. These bags were made in boxes slung in the well of a Wake twin-screw bag-barge and suspended from hydraulic cylinders. The Fig. 244. —Pier at Sunderland. Tf « S Fig. 245. —Pier at Sunderland. barge steamed alongside a conerete mixing-house, where the bag was filled with plastic conerete and laced ; the barge then proceeded to sea and was moored directly over the place where the bag was required. The box and bag were then lowered as near the bottom as possible and the bag deposited. For a length of 460 feet at the outer end of the pier, the rock was covered with a layer of sand, varying in thickness from 1 to 17 feet, and this was removed by a sand pump dredger before the bags were deposited. The pierhead is formed, in the first place, of an iron caisson, 1001 feet long, 69 feet wide, and 26| feet deep, set on a specially prepared foundation of conerete bags, levelled to 23 feet below low water. The caisson was fioated out with a draught of 22 feet, containing 3,500 tons of conerete, and sunk on its site by partly filling it witli water. It was then built up with 15-ton and 25-ton blocks, mass conerete and cement-grouted granite rubble until, when completed, its weight amounted to 10,000 tons. On top of this the pierhead superstructure was constructed in blockwork and surmounted by a lighthouse, giving a total weight of 23,000 tons for the whole structure. The new south pier (fig. 245), on the south side of the harbour is constructed in a similar manner to the Roker Pier, but varies somewhat in