Page 14 - Minutes of Proceedings of Civil Engineers Vol CXCV 1913-14 Part 1

54 WENTWoRTI{-SHEILDS oN TrrE coNsTRucTIoN or, fMinutea of jetty (berth No. 42), lay outside the old enclosing lxrnk rrnd near to the existing deep channel. The rvalls for these belths hntl to be con- structed by the aid of helmet divers. Fig. 8, Plu,te 2, shows a cross section of the rvnll adoptod for berth No.47, antl the other walls were similar though smnller. In these walls the toe rvns made shorter than in the wnll for portion A, os n longer toe u'ould have needed to be reinforced, and this could not havo been tccornplished satis- factolily under wtter'. The slope on the lxwe of the wtll was intro- duced as before, but tho steps at the lru,ck wero rn'r'anged differently, so as to frcilitn"te the divers'work. The wnll wns all formed of Port- Innd-cement concrete, partly of blocks rveighing 6 to 8 tons, and partly of moss concrete deposited under w&ter. 'l'he blocks were placed along the front and back of the wall ns facework, which extended from dock-bottom to rrbove low-water level. The mnss wolk was used in the foundation of the wall below dock-bottom and in the hearting between the blocks. Above low water the wall was also built of mass concrete, but this was deposited in the dry between tides, and not under water. The concrete mixtures used in this wall varied according to cir- cumsLr,nces, The blocks were of 6-to-1 concrete, and the mass work deposited under water 5-to-1, or, in the more exposed portions, 4-to-1. The mass work above low water was of 7-to-l concrete. For the backing of this wall special material was selected, as it lur.d to lrc tipped out into deep water. The sandy clay from the dock excavation, if used in these circumstances, would have become soft and slippery, and rvould have imposed severe pressure on the wrll. Accortlingly it was discarded in favour of a better rnaterirr,l, consisting p""1ty of broken concrete cut away from the wllls of l, dry dock which was being widened at the same time, and pnrtly of ships'tshes, which were set aside for the purpose, Dreilging and Ternporary Stages.-T.he construction of this portion of the rvall, although involving a large amount of diving work, proved to lrc fairly straightforward. The arrangement of the temporary work is shown in tr'igs. 9, Plate 2. A cut was first excavated by dredger to 35 feet below L.W.O.S.T., the bottom width of the cut being 60 feet, or 20 feet wider than the base of the wall. Temporary stages, consisting of steel girders resting on timber-pile dolphins, were next erected olong the brlck and front of the site of the wall, and just outside it. On these sbages were placed pile-drivers, grab-cranes for excavotion, nnd trv<.r 8-ton titan cranes for setting concrete blocks anrl lowerirrg rntss concrete. tr\ntsulatitn-Trenclu:t.- Frorn the temporary stages & row of timber sheet-piling rvrs driven along the back and front of the wall-site. The piles wore rnlde to penetrate to the foundation-level of the wall,