III. Fill in the words: feet, shallow, circular, mining, steel, conditions, waterproofed, cost, dangerous, downward

The … industry has been the primary constructor of shafts. Depth of several thousand … are common. In public works projects, such as sewer tunnels, shafts are usually only a few hundred feet deep and because of their high … are avoided in the design stage whenever practical … shafts find many uses. Being essentially vertical tunnels, shafts involve the same problems of different types of ground and water …. Inflowing water is far more … during construction and generally intolerable during operation. Hence, most shafts are concrete-lined and …, and the lining installation usually follows only a short distance behind excavation. The shape is usually …, although, before current mechanized excavation methods, mining shafts were frequently rectangular. Mining … is called shaft sinking. In soil, shallow shafts are frequently supported with interlocking … sheet piling held by ring beams.

FOLLOW UP ACTIVITIES

Speak on:

Basic procedures in tunneling operations.

The construction of tunnels.

Unit 8: FAMOUS TUNNELS

Lead in:

1. What famous tunnels do you know?

2. Why are they called famous?

Find the following terms and memorize their meaning.

bank blow into determination divergence draw off duct banquet brick cylinder bricklayer chamber compressed air controversy drainage enlarge exhausts engineering failure fraction heading internal combustion lining motor traffic

flooding frames impede impel inch leaks prop propel purposes survey technique temporary underwater tunnel screw sealing shaft shield shotcreting sinking surface approach