Compressed Air Work And Diving 1909

6o COMPRESSED AIR WORK. replacing the kentledge is gained. When also it is necessary to go to any great clepths, and there is a considerable area exposecl to skin friction, the kentledge required may become so great as to put an unfair stress upon the shell, which, if single, woulcl have to take the whole of the weight as a column. I he new Redheugh Bridge (1901) cylinders were also of this double type, the outsicle shell being 8 ft. in diameter and g in. thick for the top 54 ft., which portion woulcl be above ground and exposecl to the action of the air and to salt water. The lower portion, below ground, was only in. thick. The inner tube was 3 ft. in diameter. The sides of the beil inouth were designed by the engineers, Messrs Sandeman & Moncrieff, with the sides approaching more nearly to the perpendicular than was the case at Barmouth. The object was that if the caisson should sink suddenly in soft ground, the men working inside would not be knocked clown by the sides, but woulcl be shot up into the inner tube. The sides terminateel 7 in. from the bottom, and were riveteel to a 7-in. by 7-111. angle bar, which formed a ledge intendeel to prevent the too rapid descent of the cylinders in soft ground. The King Edward VII. Bridge caissons differ from the others which have been described, inasmueh as they were not circular, but conformecl to the shape of the granite masonry piers with cutwaters, which are foundeel on them. The portion of the bridge across the river is in four spåns, with a clearance of 81 ft. above high water level. 1 he two centre spåns are 300 ft. in length, and the piers supporting them are foundeel on caissons in the bed of the river. These caissons (see Fig. 10) were built of mild Steel, and were 113 ft. long over cutwaters by 35 ft.