A Treatise On The Principles And Practice Of Dock Engineering

ENTRANCES AT BARRY DOCKS. 263 inspection of figs. 188 to 192. The following interesting experience occurred during its construction :— A very large bed of running sand was met with just at the intended level of the bottom of the foundation of the north sill. The sand was so troublesome that all pumping had to be at once suspended, and the level of the bottom of the foundations raised and widened out so as to reduce the weight per unit area on the soft white tosca overlying the running sand. To overcome the difficulty an iron cylinder, 8 feet in diameter (fig. 193), was sunk through both strata into the hard tosca below, the excavation being performed by a diver. When the cylinder was well down, a good layer of strong concrete was put in, making the cylinder quite watertight below, while it was allowed to receive by lateral holes the drainage from the upper white tosca, at a level between the bottom of the foundations and the top of the running sand. A centrifugal pump, working continuously, kept the water in the cylinder below foundation level. Before building the masonry of the north sill, the entire surface was covered with a layer of concrete, 25 inches thick. Laying the concrete in bags, which was the method first attempted, did not succeed, and canvas in long strips was sub- stituted, with the joints so placed that the water would run underneath. This plan answered well, and although the level at which the canvas was laid was only 2 feet above the running sand, the whole of the concrete was put in quite dry. When the invert was completed, the cylinder was filled with concrete and built over. Eastham Entrance Locks. Manchester Ship Canal.—There are three entrance locks (fig. 194) con- structed in parallel lines pointing down the River Mersey, 600 feet by 80 feet, 350 feet by 50 feet, and 150 feet by 30 feet, respectively. The lower sill of the largest lock is 42 feet below high water of ordinary spring tides. This lock has culverts on each side, 12 feet high by 6 feet wide, which enable it to be filled or lowered, so that a vessel can pass through in less than ten minutes. Two 20-foot Stoney sluices adjoin the locks and assist to fill and lower the canal at tide and flood times respectively. Entrances at Kidderpur Docks, Calcutta. Plans and sections ef the entrance locks and passages at these docks which have already been referred to (p. 236) åre shown in figs. 195 to 200. Entrances at Barry Docks. The harbour is approached by a sheltered channel, 450 yards long, enclosed by two breakwaters, the heads of which are 350 feet apart. There are two entrances—one, leading to a basin, is available for 2^ hours before and 2| hours after high water ; the other, known as the Lady Windsor