Methods of Quarrying

The following methods of quarrying are listed based on the outcrop of the rock and the purpose for which stones are intended to be used.

1. Digging

In soft rocks, stones are obtained merely by digging with the help of hand tools, viz., pick-axes, hammers, chisels, etc. Only those stones that occur in the form of detached nodules buried in the Earth can be easily quarried by this method.

2. Heating

This method is adopted by burning certain kinds of fuel (usually wood is used) and the exposed surface of the portion of the rock to be separated. On burning for several hours continuously, due to unequal expansion of the rock, the rock gets separated from the cold mass with a dull noise. The detached portion is then removed and made to the required sizes by using quarrying tools. This method is employed for obtaining road metals, ballast for railways and aggregates for concrete.

3. Wedging

Soft stratified rocks can be removed by wedging as these rocks are in the form of layers and are easy to split. Soft rocks are removed with the help of pick axes and crow bars. Limestone, marble, slate and laterite are removed by this simple method.

In hard rocks, holes are made and grooves are cut at shorter intervals. Blunt wedges are inserted into the grooves and are forced to get separated. Alternatively, conical pairs of steel are driven into the holes with a hammer and further force to get separated. In the case of very hard stones, the holes are originated by a pneumatic drill.

4. Blasting

This technique is employed for quarrying hard and compact rocks. Blasting is done in stages as discussed below.

Holes may be made with a steel bar with knife-edged ends called jumpers. In case large quantities of stones are required, holes may be drilled by a drilling machine. In order to facilitate the operation, water is used. The slurry produced as a result of drilling is removed by a scraper or a spoon or by a compressed air blast.

The drilled holes are charged with an explosive of suitable capacity. It is necessary for the holes to be made a day before charging with explosive.

Tamping of the explosives is done before firing in order to prevent the blasting within the hole itself. Tamping consists of filling the hole with stiff sandy clay and tamping with a brass rod. A fuse is inserted to fire the explosive. While tamping, a small quantity of gun powder is sprinkled to link the explosive to the bottom of the fuse.

The fuse is fired carefully. During the explosion, masses of stones around the hole are removed. A properly packed explosive shall produce a dull sound followed by displacing of the mass of rock around it.