Tunneling

Tunneling: A Practical Treatise is by Charles Prelini, with 167 illustrations, in a sixth edition, revised and enlarged. The text says the shield was invented and first used by Sir Isambard Brunel in excavating the tunnel under the River Thames at London, which was begun in 1825, and finished in 1841. Under the heading Choice Between a Tunnel and an Open Cut, the text says that when a railway line is to be carried across a range of mountains or hills the first question which arises is whether it is better to construct a tunnel or to make such a détour.

The text says two standard forms of centers are employed in the English method. The text says that the crown bars are not pulled ahead their full length at one operation, but are advanced by successive short movements as the excavation progresses. The text says the quantity of air required for breathing purpose and explosions is as follows: 1 workman with lamp needs 240 cu. yds. of fresh air in 24 hours.