Comprehension check.

I. Decide whether the following statements are true or false according to the text.

1. Submerged tunnels lie in the trenches dug through rock.

2. Blasting is one of the main methods used in the construction of rock tunnels.

3. The length of the holes varies from 2 to 5 meters.

4. After the explosion it is always necessary to construct a support.

5. Rings of steel beams or timber can prevent large fragments of rock from falling.

6. Tunnel-boring machines dig tunnels in sandstone.

7. Tunneling through soft earth is more dangerous than through rock.

8. Concrete sections are always used in earth tunnels.

9. When the air pressure inside the tunnel is equal to the pressure of the water outside, the water is kept out.

10. Submerged tunnels are the cheapest.

II. Answer the following questions.

1. What is done first to blast the rock?

2. How are holes bored?

3. Where do workers pack explosives?

4. When doesn’t the tunnel require extra support?

5. Why do workers insert long bolts through the rock?

6. How does a tunnel-boring machine work?

7. When do worker hold the soil in place with bolts, steel ribs and sprayed concrete?

8. Tunneling beneath bodies of water is more dangerous, isn’t it?

9. What tunnels are cheaper?

10. Do you know any submerged tunnels?

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