Engineering Wonders of the World
Volume I

62 ENGINEERING WONDERS OF THE WORLD. to buildings above was avoided. We may add here that the tunnel ran below the South Metropolitan Gas Works and other large buildings without affecting them in any way. Under favourable conditions the operations described took place four times in twenty- four hours, the shield advancing 10 feet in the tunnelling, and very little illness was caused by the use of compressed air. Tunnelling started from No. 3 Shaft in February 1906, and the shield reached the other side of the river in November of the same year. The conditions were similar to those met with in the pilot tunnel, and the MAKING RUST JOINTS BETWEEN RINGS. that time. To attain this result about seventy- five men were usually employed in the tunnel, Rate of Progress. greater part ground. No in three shifts of eight hours each. Most of these men were accustomed to tunnelling, many of them having spent the of their working lives under- fatal accident occurred during air pressure used was about the same. The lining of the small tunnel was taken out in front of the large shield as it progressed. While the big shield was working its way under the river-bed, a second of equal size had been erected in Shaft No. 3. By the time that the first shield had run its subaqueous course, the second was ready for action, and so the