A Treatise On The Principles And Practice Of Dock Engineering

CONSTRUCTION IN THE OPEN. 197 righted again by the excavation.” Old rails and kentledge were used as sinking weights. The heaviest load was 350 tons. Having reached a satisfactory depth, a little copper slag was put in the bottom of the wells prior to filling the whole with 7 to 1 concrete containing rubble. Small bags of concrete were packed by divers all round the toe under the curb, and then the bulk of the concrete was lowered in skips through the water to the bottom, and gently released. Ihe intervening spaces of about 2 feet between adjacent piers were piled, back and front, and concreted. The superstructure consisted of a sandstone ashlar facing, backed by 5 to 1 cement concrete with granite coping. The face has a batter of I in 12.* General Methods of Construction. Apait from the means adopted to secure a firm and reliable foundation on sites more or less unsatisfactory and untrustworthy, there are a great variety of methods practised in constructing the dock wall itself : so varied, in fact, as to scarcely admit of any classification, though an attempt will be made here to include some of the more prominent and typical systems under five heads, viz. :— (a) Ordinary construction —■ In the open. In trenches. Within temporary dams. (ß) Subaqueous construction — In pneumatic chambers. With monoliths. Construction in the Open.—A description of this method calls for little or no amplification. Where the base rests upon the natural surface of the ground, the wall, if of masonry, is built in the ordinary way, generally with the aid of overhead travellers. If of concrete, it will be necessary to provide means for the support of the face moulds. This may be done by the use of temporary uprights, sometimes called “ soldiers.” These uprights (fig- 39), placed at convenient distances apart, have a rebate on their inner faces, within which the moulds are free to move vertically. When the latter have been lifted or lowered to their assigned position, they are temporarily fixed by means of wedges. The swivel hooks shown in the fig. are for the purpose of raising the moulds. Alternatively, the moulds may be supported by wooden cantilevers built into the wall at each succeeding course, as shown in fig. 38, and temporarily counterweighted by concrete blocks. These cantilevers can be afterwards cut away to an inch or so within the face line * Scott on “ Deep-water Quays, Newcastle-on-Tyne,” Min. Proc. Inst. C.E.. vol. exix.