II. Match the words with their opposites.

1. Solid a) pack

2. Extract b) remote

3. Add c) cheap

4. Long d) behind

5. Complete e) separate

6. Expensive f) permanent

7. Connect g) start

8. Ahead h) short

9. Temporary i) soft

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.

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Basic procedures in tunneling operations.

Дата добавления: 2015-08-27