A Treatise On The Principles And Practice Of Dock Engineering

220 DOCK ENGINEERING. of underpinning operations as carried out at certain of the Liverpool docks. Owing to the exigencies of traffic the work had to be done in sections, with the dock full of water, so as to interfere as little as possible with shipping accommodation. Fig. 160 shows a section of the old wall, at the commencement of the underpinning, and fig. 161 is a section of the completed undertaking. It will be observed that the work was carried on under cover of a sheeting dam, described elsewhere (p. 105, ante), strutted and shored to the old wall, at a distance of about 17 feet. Below the level of the dock bottom, an inner trench was exeavated between two rows of sheet- ing piles, one of which was situated at the extreme back of the wall and the other in front of it. Within these limits the underpinning was effected on similar lines to the underbuilding at Ardrossan. The bays were from 10 to 15 feet in length and were dealt with singly, the work being attacked at several points simultaneously. The new work consisted entirely of 6 to 1 concrete, carefully tongued into the old masonry, the surface of which was well washed and picked rough. When the concrete had been deposited to within 3 feet of the underside of the existing base, the remaining layer was put in, in three sections, advanc- ing from the back towards the front, behind roughly constructed barriers of rubble, the concrete being carefully rammed tight and the whole grouted. Miscellaneous Types of Wall.—It will be as well to conclude the chapter witli some miscellaneous examples of the very varied range of types to be found among dock walls. Figs. 162 to 164 are plan and sections of the Albert Dock wall at Hull,* or, rather, the wall as originally designed and only executed for a part of its length, owing to modifications introduced as the work proceeded. This type of wall with an arched front is unusual, and it has obvious inconveniences, though as regards its structural qualities, a broad base with a minimum of masonry was held to counterbalance these drawbacks on a foundation which was incapable of sustaining much pressure. A similar type of wall, consisting of alternate piers and arches, is to be found at Bordeaux. The sections (figs. 165 and 166) of two dock walls at Greenock are self- explanatory and do not call for any remarks, except that it may be well to add that the quarry refuse filling behind the western tidal harbour Hawkshaw on “The Albert Dock, Hull,” Min. Proc. Inst. C.E., vol. xli.