Geologically, how many classes of tunnels are recognized?

Folded rocks are often best storehouses of which of water?

Which type of rocks requires double lining, i.e., temporary and permanent lining?

Underground excavations for carrying pipes, sewage etc. fall under which type?

Which outline is preferred for weak rocks with unequal lateral pressure?

Method of placing tubes in public utility tunnels is called ______

In synclinal condition, low pressure areas are found at ______

Which type of strata is rare in occurrence?