English+02.+tipos+de+tuneles

1.Who built the first tunnels and why they were built? Roman engineers created the most extensive network of tunnels in the ancient world. They built sloping structures, called aqueducts, to carry water from mountain springs to cities and villages

2. What are the basic types of tunnels? : son tres tipos de túneles,
 * Soft-ground tunnels**:are typically shallow and are often used as subways, water-supply systems, and sewers
 * Rock tunnels**:require little or no extra support during construction and are often used as railways or roadways through mountains
 * Underwater tunnels**:are particularly tricky to construct, as water must be held back while the tunnel is being built. Early engineers used pressurized excavation chambers to prevent water from gushing into tunnels.

3. What are the forces that act on each type?:
 * Soft-ground tunnels:**The heavy, wet ground pushes on all sides of the tunnel. The tunnel's walls are squeezed by the ground
 * Rock tunnels:**The rock walls are very dense and can support themselves. Some sections of the rock are less dense than other sections. These loose chunks of rock push on the sides of the tunnel.
 * Underwater tunnels:** Water pushes on the sides of the tunnel. The tunnel's walls are squeezed by the water.

4. What are the basic steps that an engineer must follow when building a tunnel? :three basic steps to building 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.