A Treatise On The Principles And Practice Of Dock Engineering

4/8 DOCK ENGINEERING. intervals of 3 feet or more. Under the keel-blocks, the piling is still more concentrated. Their heads having been cut off to a uniform level, the piles are connected by longitudinal and transverse beams some 12 inches square, upon which is laid the 3-inch planking forming the floor surface. The pile- tops and the longitudinals are bedded in concrete provided with a smooth sloping surface to drain off the water. Square balks, set at an angle of about 40 degrees, form an inclined foundation for the altar courses at the sides of the dock. The courses have vertical and horizontal faces and splayed undersides. The supporting timbers are carried on rows of piles, pitched about a yard apart. Above the concrete under floor level, the sides are backed with clay-puddle, confined within a second and outer row of sheet-piling driven well down below the floor level. A combination of timber, stone, and concrete construction is exemplified at a graving dock (fig. 461) at Halifax, Nova Scotia.* The substratum of the dock is rock, and it was proposed to form a floor of concrete upon this Fig. 461. —Section of Graving Dock at Halifax, Nova Scotia. Scale, 50 feet = 1 inch. foundation, 2 feet thick, but, to meet the wishes of the City Corporation, a pitchpine floor was substituted, laid on sleepers bolted to the concrete, which was reduced to a minimum thickness of 12 inches. “The flooring has proved a great convenience, as, when the dock is pumped out, the water drains away from the surface immediately.” Above the rock level the walls consist of rubble-in-cement backing, and they are faced with concrete, 3 feet thick, from top to bottom, the altars being capped with granite, 12 inches thick. Mud docks of a very primitive description are apparently still in use at some insignificant oriental ports, but they do not call for any serious notice. Types of Floating Docks. The earliest floating docks were of wood, with a sectional profile resembling that of a ship. They were fitted with a pair of gates at one end, which were closed after the entrance of a vessel, and the impounded water was then pumped out. Wooden docks of a later type are known as the “ Sectional Dock ” and the “ Balance Dock.” * Parsons on “ Halifax Graving Dock, N.S.,” Min. Proc. Inst. C.E., vol. cxi.