1.7. Read the text “Major Types of Tunnels” and find the answers to the following questions.

1. What are the basic steps to build a stable tunnel?

2. In what groups can all tunnels be divided according the setting?

3. Are soft-ground tunnels typically shallow or deep?

4. Do rock tunnels require little or extra support during construction?

5. Are underwater tunnels tricky to construct?

6. What groups can all tunnels be divided into according to their purposes?

Major Types of Tunnels

Today, engineers know that there are three basic steps to build a stable tunnel. The first step is excavation: engineers dig through the earth with a reliable tool or technique. The second step is support: engineers must support any unstable ground around them while they dig. The final step is lining: engineers add the final touches, like the roadway and lights, when the tunnel is structurally sound (прочный).

Based on the setting, tunnels can be divided into three major types:

Soft-ground tunnels are typically shallow and are often used as subways, water-supply systems, and sewers (канализационная труба). Because the ground is soft, a support structure, called a tunnel shield, must be used at the head of the tunnel to prevent (предотвращать) it from collapsing.

Rock tunnels require little or no extra support during construction and are often used as railways or roadways through mountains. Years ago, engineers were forced to blast through mountains with dynamite. Today they rely on (полагаться на) enormous tunnel boring machines.

Underwater tunnels are particularly tricky (хитроумный) to construct, as water must be held back while the tunnel is being built. Early engineers used pressurized excavation chambers (камеры) to prevent water from gushing (фонтанирование) into tunnels. Today, prefabricated tunnel segments can be floated (размещены) into position, sunk (погружены), and attached (присоединены) to other sections.

According to their purposes all tunnels can be divided into three broad categories: mining, public works and transportation.

Mine tunnels are used during ore extraction, enabling laborers or equipment to access mineral and metal deposits deep inside the earth. These tunnels are made using similar techniques as other types of tunnels, but they cost less to build. Mine tunnels are not as safe as tunnels designed for permanent (постоянный) occupation.

Public works tunnels carry water, sewage (сточные воды) or gas lines across great distances. Some tunnels are aqueducts to supply water for consumption (потребление) or for hydroelectric stations or are sewers. Other uses include routing power or telecommunication cables. Secret tunnels have given entrance to or escape from an area. Some tunnels are not for transport at all but rather, are fortifications (укрепления).

Before there were trains and cars, there were transportation tunnels such as canals – artificial waterways used for travel, shipping or irrigation. Just like railways and roadways today, canals usually ran above ground, but many required tunnels to pass efficiently through an obstacle, such as a mountain. Canal construction inspired some of the world’s earliest tunnels. By the 20th century, trains and cars had replaced canals as the primary form of transportation, leading to the construction of bigger, longer tunnels.