Compressed Air Work And Diving 1909

KING EDWARD VII. BRIDGE. 65 were high enough to allow pins to be put through at the level of the top of the thirty-two little cast-iron saddles which were placed on the top of the box girders. 1 he valves of the rams were then openecl and the weight taken by the pins resting on the cast-iron saddles. The packings underneath the cutting eclge were then knocked out and the timber cantilevers sawn through at ff. The weight was again taken by the rams, the pins at the level of the top of the cast-iron saddle were withdrawn and placed in the holes 18 in. higher up, hh, and the caisson was then lowered 18 in. until the pins at hh rested on the cast-iron saddles. I he top pins bb were then withdrawn and placed at ll, the rams were pumped up, the weight of the caisson taken by them, and the bottom pair of pins withdrawn and placed in the next pair of holes higher up. The pressure of water in the rams was again taken off and the caisson lowered another 18 in. This operation was repeatecl until it was floating in the water. Sufficient concrete was then put in above the working chamber to cause the caisson to sink. I he excavation was then commenced. In two of the caissons the concrete was carried to a height of about 50 ft. from the cutting edge, and in one —the centre pier caisson—to about 26 ft. from the cutting eclge. But in this caisson 16 ft. high of the granite pier had to be set also in order to give the necessary kent- ledge. All the plant in connection with the caisson sinking was electrically driven. In the United States of America pneumatic caissons are commonly constructed of timber. Por the construc- tion of a stone-arched bridge at Hartford, Connecticut (1904), caissons 29 by 143 ft. were employed. The height of the working chamber was 6 ft. The ceiling was made of three thicknesses of 12 by 12 in. yellow pine timber,