A Treatise On The Principles And Practice Of Dock Engineering

498 DOCK ENGINEERING. There are two culverts for filling the dock, one in each aide wall, with a sectional area of 87 square feet, closed with vertical paddles of the ordinary type, working in granité grooves. Each paddle consists of a built-up mild steel frame, covered with tongued and grooved oak planks and provided with greenheart rubbing fillets. Canada Graving Dock at Liverpool. The extreme length of the dock (figs. 500 and 501) from point of sill to head of dock is 925 feet 6 inches. It has an entrance width of 94 feet and a depth of water of 32 feet at high water of ordinary spring tides. The height of the pierheads is 41 feet above sill level. In the interior of the dock the bottom width is 94 feet, whence the side walls recede in a series of thirteen offsets, or altar courses, of irregular height, to a width of 124 feet 2 inches at coping level. The coping level is 35 feet 8 inches and 36 feet 1 inch above sill level on the north and south sides of the dock respectively. Communication with the bottom is made by means of six sets of stone steps and slides, three at each side, and there are also two stairways at the head of the dock. The floor of the dock has a fall of 9 inches from the centre to the sides, where drainage channels communicate through 18-inch drain pipes with the two central culverts. These are parallel to each other, and to the longi- tudinal axis of the dock, commencing with a section, 4 feet by 3 feet, of which the sides are vertical and the roof and floor curved, passing through the circular form with 5 feet 6 inches diameter, and finally assuming an egg-shape, 8 feet deep. A rectangular pit, 12 feet by 35 feet open save for an iron grating, receives the water from the dock at its north-west corner, whence it is transmitted by two large rectangular culverts, each 10 feet 9 inches by 9 feet, to the pumping well at a level of 18 feet below the sill. The pumping plant consists of three 51-inch centrifugal pumps, each driven by a condensing engine of 700 H.P., with two high-pressure cylinders, 25 inches diameter and 2 feet stroke. Steam at 110 Ibs. pressure is supplied from six sets of Babcock and Wilcox patent water-tube boilers, having 3,116 square feet of heating surface and 59^ square feet of grate area to each boiler. The pumps are capable of lifting 1,000 tons per minute, and of emptying the dock, whose capacity is 3,226,648 cubic feet, in an hour and a-half. There is also a small 14-inch drainage pump for dealing with leak- age, which is very slight. The bulk of the walls and floor are of concrete, composed of 1 part of Portland cement to 6 and 8 of Harrington gravel, faced with 2 to 1 concrete, and having granite coping, quoins, sills, steps, and slides. The keel-blocks are of cast-iron wedges, surmounted by a birch cap 12 inches thick. The top of the blocks is 4 feet above the floor level. The entrance is closed by green- heart gates, and the clough paddles are also of greenheart. Behind the gate heel-posts are two culverts for filling the dock.