The underground routes or passages driven through the ground without disturbing overlying soil cover are called ______

Which type of strata is rare in occurrence?

Traffic tunnels are always constructed for kilometres.

Tunnels associated with hydropower generation are called ______

Geologically, how many classes of tunnels are recognized?

When can the rocks act as a natural arch?

Type of hydropower tunnel where water is conveyed under gravity is ______

In synclinal condition, low pressure areas are found at ______