Compressed Air Work And Diving 1909

B ARMOU TII BRIDGE. 59 fresh water spring the air pressure had to be raised to 46 Ibs. This is the greatest pressure at which work of this clescription has been carried out in this country, and in spite of this faet, and that on account of the open nature of the ground the pressure coulcl not be lowered below that of the head of water outsicle, as is possible on some work, there were no fatal cases of caisson disease, and only one case of paralysis, from which recovery was complete. The men worked at the highest pressure for one and a half hours at a time twice a clay. When the sinking was completed the bell mouth working chamber and inner tube were fillecl with concrete under pressure before the removal of the lock. The lock itself (Fig. 9) consisted of a circular plate bolted to a special short length of cylinder, and had an inverted D-shaped entrance chamber for men and material. The air valves were so arrangeel that the pressure in the entrance chamber coulcl be raised or lowered either from the top or, by authoriseel persons, from inside the chamber. The inside of lock, entrance chamber, and working chamber were lighted electrically. For the remaining piers of the bridge, it was not con- sidered necessary to go clown to rock level, as a slight settlement would not, with them, be of serious conse- quence. Cylinders with a -f-in. thick single shell were therefore adoptecl, and after these had been sunk by the compressed air method, piles were driven rouncl the cutting edge in the open, and the interiörs then filled up with concrete in the usual way. The type of cylinder built up with Steel plates and with an inner shell is perhaps the best that can be adoptecl. The rate of sinking will be faster, because when moving the lock to aekl fresh lengths, the time which would otherwise be wasted in taking off and