The re-modelling of graving dock at Southampton

The Graving Dock known as No. 3, which forms the subject of this paper, was built in 1853 from the design of the late Mr. Alfred Giles, Past President Inst.C.E., and was lengthened to its present dimensions in 1882. It is shown on the plan and section, Figs. 1 and 2. It has an inside length of 520 feet and a width at entrance of 80 feet. The keel blocks are placed at a level of 24 feet below H.W.O.S.T., the blocks themselves being 3ft. 3in. high. The Dock is closed by a pair of wrought iron gates which, when opened, lie back in recesses, and when closed shut against a stone cill which is raised about 2ft. 6in. above the rest of the floor. From the cross-section it will be seen that the walls are 15 feet thick at the base, and that they are reduced by means of three sets of altars to a thickness of 5 feet at the top. The floor has the shape of an inverted arch, and formerly contained five small altars or steps on each side. The walls are constructed of brickwork in lime mortar. The floor consists of the same material for a thickness of 4 feet, and below that of a similar thickness of lime concrete. The altars are capped with Portland roach stone, and the coping of the walls and the hollow quoins, against which the gates rest, are of the same material. The cill is of Bramley Fall sandstone, which was considered to be a very fine building stone at the time the dock was built. It is curious that granite, although much used in the older docks at Southampton, is hardly seen in this particular dry dock. There are no precise records of the nature of the subsoil on which the dock is placed, but there is no doubt that it consists either of a weak sandy clay or of a fine running sand, both of which strata prevail in this neighbourhood. It is probable that fine sand highly charged with water occurs under most of the floor. This conjecture is confirmed by the fact that at the south end of the dock there are two vertical holes through the brickwork of the floor through which water is constantly coming up. R. N. Sinclair