A Treatise On The Principles And Practice Of Dock Engineering

502 DOCK ENGINEERING. backing. Numerous joints and fissures were exposed by the excavations in the hard mari and limestone, and from some of these sait water issued. Under the foundations of the west wall of the inner dock a cavern, 27 by 23 feet and 14 feet deep, was discovered in the mari, through a hole in which, sea water burst forth and continued to flow at eacli tide, but ceased at low water of spring tides. A brick wall in cement mortar was built round the hole at the top of the cavern to keep in the water. Rubble stones were then deposited in the cavern, and a Portland cement concrète floor, 6 feet thick, was laid on them, and on this the wall is founded. The floor is of Portland cement concrete, 6 to 1, and 2 feet in thickness, with stone drains. Across the floor, in and under the concrete, 4-inch land drains are laid, 20 feet apart, to convey any rising water to the open drains. The walls are built of mountain limestone, weighing 169 Ibs. per cubic foot, from the Alps quarry, about 5 miles away. The roughly-dressed face- stones are squared but not laid in courses, and have close beds and joints for 6 inches, lipped with cement for 3 inches inwards at the time of building. The remaining portions of the walls are built in blue lias lime mortar. Headers, not less than 3^ feet long, pass through from front to back and overlap each other. The altars, 2 feet by 9 inches, and the coping are of granite. The depth of the dock from coping level to floor is 32 feet 6 inches. The walls have not been designed to resist water pressure from the back, and cast-iron pipes are inserted in them to allow the water to escape. Any reflex action is prevented by brass clack-valves. There are wrought-iron ladders connecting the altar courses and flights of wooden steps in the corners for access to the floor. The walls of the entrance have a batter of 1 in 8. The sill stones and caisson quoins are of granite, fine-axed on the meeting face. The bearing blocks for the bottom of the caisson are limestone, 2 feet by 15 inches, standing 1| inches above the concrete floor, 6 feet apart centre to centre, and level throughout. Hydraulic pipes and electric light mains are carried in a recess, 8 feet wide and 18 inches deep, in the walls and across the invert. The last-named is built in brickwork with cement mortar, faced with two- courses of Staffordshire blue bricks. Beneath the engine and boiler house (fig. 505) are the suction and discharge chambers, 10 feet wide and 11 feet high, with floors 3 feet 6 inches lower than that of the graving dock. Two culverts, 6 feet 6 inches in width and height, conduct the water to the suction chamber and a similar sized barrel-culvert conveys the water from the suction chamber to the sea. There are three suction pipes in the pumping chamber, 33 inches diameter, and three similar discharge pipes in the discharge chamber. In addition, there are two suction pipes and one discharge pipe, 12 inches diameter, connected with the two drainage pumps. The pumps consist of three 33-inch horizontal, high-pressure condensing, centrifugal pumping engines and two- 12-inch drainage, centrifugal pumping engines, supplied with steam from three Lancashire boilers and one auxiliary Oornish boiler. The main.