Canadian engineer . sides. When everything wasclear below the shoe, the blow-pipes were opened and theair pressure lowered three or four pounds. The weight ofconcrete on top was so regulated that the caisson would then L February 29, 1912. THE CANADIAN ENGINEEE 339 settle down on to the hard bench below the shoe. Clay wasthen used to mud-up underneath the shoe, to prevent theleakage of air; and excavation commenced again. About 900 cubic yards of material was excavated fromNo. I caisson, including about 50 cubic yards of bed rockwhich had to be blasted out in one end of the caisson to geta lev
Canadian engineer . sides. When everything wasclear below the shoe, the blow-pipes were opened and theair pressure lowered three or four pounds. The weight ofconcrete on top was so regulated that the caisson would then L February 29, 1912. THE CANADIAN ENGINEEE 339 settle down on to the hard bench below the shoe. Clay wasthen used to mud-up underneath the shoe, to prevent theleakage of air; and excavation commenced again. About 900 cubic yards of material was excavated fromNo. I caisson, including about 50 cubic yards of bed rockwhich had to be blasted out in one end of the caisson to geta level bearing for the pier. When the excavation was completed, the work of con-creting the caisson began. The concrete was poured on tothe bottom door of the material locks and then dropped intothe caisson. Wet concrete was used until the caisson wasfilled to within four feet of the deck. It was then sent downvery dry; and benched and packed tight against the deck,leaving a narrow passage down the centre. This passage. 6. Excavating Stone. was then packed full, up to the locks and the air taken weeks was the average length of time required to exca-vate and concrete each caisson. Two other caissons of the same construction were sunkfor the McKellar bridige. These caissons, however, *^entdown 45 feet and required 18 lb. pressure. Mr. A. C. Stewart was in charge of the work ; the writerwas contractors engineer; and G. N. W. Otty, , resi-dent engineer for the Canadian Pacific Railway. NEW OCEAN DOCKS. Messrs. Harland and Wolff, the famous Belfast ship-buildino- firm, intend to establish ship repairing works atLiverpool. At a meeting of the Mersey Docks and Harbor Board, itwas recommended by a committee that the North dock yardat Bootle should be let to Messrs. Harland and Wolff, andthe motion was adopted. The site has been taken on asixty years lease. It will not be necessary to construct anew dock in connection with the scheme. Lord Pirrie, head of Harland and Wolff, is
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