History The use of explosives in mining goes back to the year 1627, when gunpowder was first used in place of mechanical tools in the Hungarian (now Slovakian) town of Banská Štiavnica. The innovation spread quickly throughout Europe and the Americas. While drilling and blasting saw limited use in pre-industrial times using gunpowder (such as with the Blue Ridge Tunnel in the United States, built in the 1850s), it was not until more powerful (and safer) explosives, such as dynamite (patented 1867), as well as powered drills were developed, that its potential was fully realised. Drilling and blasting was successfully used to construct tunnels throughout the world, notably the Fréjus Rail Tunnel, the Gotthard Rail Tunnel, the Simplon Tunnel, the Jungfraubahn and even the longest road tunnel in the world, Lærdalstunnelen, are constructed using this method. In 1990, 2.1 million tonnes (2.32 million short tons) of commercial explosives were consumed in the United States, representing an estimated expenditure of 3.5 to 4 billion 1993 dollars on blasting. Australia had the highest explosives consumption that year at 500 million tonnes (551 million short tons), with Scandinavian countries another leader in rock blasting (Persson et al. 1994:1).
Procedure As the name suggests, drilling and blasting works as follows: A number of holes are drilled into the rock, which are then filled with explosives. Detonating the explosive causes the rock to collapse. Rubble is removed and the new tunnel surface is reinforced. Repeating these steps until desired excavation is complete. The positions and depths of the holes (and the amount of explosive each hole receives) are determined by a carefully constructed pattern, which, together with the correct timing of the individual explosions, will guarantee that the tunnel will have an approximately circular cross-section. During operation, blasting mats may be used to contain the blast, suppress dust and noise, for fly rock prevention and sometimes to direct the blast.
Rock Support As a tunnel or excavation progresses the roof and side walls of need to be supported to stop the rock falling into the excavation. The philosophy and methods for rock support vary widely but typical rock support systems can include: Rock bolts or rock dowels Shotcrete Ribs or mining arches and lagging Cable bolts In-situ concrete Typically a rock support system would include a number of these support methods, each intended to undertake a specific role in the rock support such as the combination of rock bolting and shotcrete.