Explosives used for rock blasting

Rock drilling and blasting is the controlled use of explosives and other methods such as gas pressure blasting pyrotechnics, to break rock for excavation. It is practiced mostly in mining, quarrying and civil engineering such as dam, tunnel or road construction. The result of rock blasting is commonly known as a rock cut.

Rock blasting uses a variety of explosives with varying compositions and performance properties. Higher velocity explosives are utilized for relatively hard rock in order to shatter and break the rock, while low velocity explosives are utilized in soft rocks to generate more gas pressure and a greater heaving effect. For example, an early 20th-century blasting manual compared the effects of black powder to that of a wedge, and dynamite to that of a hammer. The most commonly used explosives in mining today are ANFO based blends due to their lower cost than dynamite.

Prior to the advent of tunnel boring equipment, drilling and blasting was the only economical way of excavating long tunnels through hard rock, where digging is not possible. Even today, the method is still used in the construction of tunnels. The decision whether to construct a tunnel using a tunnel boring machine or using a drill and blast method includes a number of factors. Tunnel length is a key factor that must be addressed because large tunnel boring machines for a rock tunnel have a high capital cost, but because they are usually quicker than a drill and blast tunnel the price per metre of tunnel is lower. This implies that shorter tunnels tend to be less economical to construct with a tunnel boring machine and are therefore, usually constructed by drill and blast. Managing ground conditions can also have a significant effect on the choice with different methods suited to different hazards in the ground.


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