Blasting activities are carried out in mine fields, be it underground or Open pit. It consists of reducing a solid body such as rocks into small fragments using explosives.
A conventional blasting operation always include the following operations:
- Drilling holes
- Placing a charge and detonator in each hole
- Detonating the charge
- Clearing away the broken material
When an explosive detonates, its chemical energy is released, turning the compact explosive into a highly pressurised, incandescent gas. This pressure can rise above 100,000 atmospheres in a hole that is closely packed.
The drill hole’s surrounding area is broken apart by the intense pressure, exposing the surrounding rock to extreme stresses and strains that lead to the formation of cracks. The rock in front of the drill hole yields and advances as a result of the fissures widening due to the gas pressure. The rock in front of the hole will break loose if the gap between it and the nearest surface is not too great.
The placement of the holes ensures that a minimum amount of explosive is needed for every volume of rock broken (referred to as the powder factor). The majority of blast-hole designs stem from the observation that fragmentation is most consistent when the detonating charge is located a specific distance away from an exposed rock face. Charges are inserted into a sequence of holes that are drilled so that, when the holes closest to the exposed surface are fired, the blasts form new exposed faces at the appropriate distances from the following set of holes, in which the firing of the charges is somewhat delayed, in order to break up a big body of rock. The holes are shot at very short intervals of time, following a predefined order.
Common applications for blasting include the breaking of materials like coal, ore, stone, or other mined minerals; building demolition; and excavating foundations for civil projects.
