Compressed Air Work And Diving 1909

RO TITERIII THE TUNNEL. *5 the head of water and the air pressure. What might perhaps happen in a shielcl of this design, should an inrush of water take place, is that the traps would become fillecl with silt and mud which woukl check the outflow of air, and allow the pressure to rise suffi- ciently to stop the water coming in. In the centre of the river the tunnel was only 7 ft. below the bed of the river. In the case of the Blackwall Tunnel the Thames Conservancy allowed about 10 ft. of clay to be deposited on the river bed, but in the present case, on account of the works being opposite the Surrey Commercial Docks and the London Docks, they were unable to grant permission for any clay to be deposited. This 7-ft. cover was composeel of sand, and the work had therefore to be carried out with great care, and so carefully was the work done that at no time did the water break in. At the lowest point in the line of the tunnel the level of the crown was 48.67 ft. below high water mark, and the deepest shaft, No. 2, was carried clown to a depth 96.56 ft. below high water mark. The section of tunnel under the river, about 1,500 ft., was completed in nine months. On several occasions 12 ft. 6 in. was completed in the twenty-four hours, and 267 ft. was completed during the month of October 1906. All the work under compressecl air was carried on in three shifts of eight hours each. At one time there were 800 men engaged on the works and of these about 450 were working in compressecl air at one time, or about 150 men per shift. The tunnel lining is composeel of cast-iron segments bolted together, each ring is 2 ft. 6 in. wide, external diameter 30 ft., diameter between flanges 27 ft. 8 in. The thickness of the metal in the bodyCof the segments