Shafts, which are generally vertical, are usually distinguished from tunnels , which are horizontal.
Little difficulty is experienced in shaft sinking through solid rock, which contains little water.
When loose, water-bearing strata have to be contended with, careful shoring and sealing of the shaft lining become necessary, and pumping facilities are needed. Shafts are usually circular or rectangular and are generally lined with wood, masonry, concrete, steel, or cast iron. Shaft sinking through rock is generally accomplished by blasting. When the loose surface material has been removed, holes are drilled, and the charges are placed and are fired by electricity. The broken rock is removed and the process is repeated.