Blasting in mining involves the chemical and physical process of detonating explosives to break mineral-bearing materials like coal and ore. Explosives can be placed in drill holes or on the rock surface, impacting blasting efficiency. Solid blasting, utilizing specific shot hole patterns and detonators, presents advantages like low capital costs and flexibility despite drawbacks such as lower coal output and higher explosives consumption.
Fremont, CA: Blasting in mining involves a chemical and physical process achieved by detonating explosives and breaking mineral-bearing materials such as coal, ore, and mineral stone. This process fragments materials, dislodges rock blocks, and demolishes existing structures.
Explosives placement can occur in drill holes within the rock mass or on the surface. The effectiveness of blasting depends on the precise location of the explosives. The charge placement in a borehole requires a specific charge, which can vary from up to ten times in excess to at least three times for an appropriate lay-on charge. Blastholes, cylindrical openings drilled into rocks for explosives placement, require dewatering before charging, achieved through compressed air-operated pumps or electrical submersible impellent pumps.
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Prescribing a specific blasthole inclination is vital for effective blasting. In some cases, angled holes are used to break the toe and achieve better fragmentation, leading to reduced drilling and blasting costs due to increased burden and a stable bench edge. The blaster or shotfirer, a qualified individual, is in charge of the blast. This article delves into explosives used in mining, air blasting, and solid blasting techniques.
Chemical compounds or mixes that react quickly to release heat and gas and create high pressure are called explosives and are employed in mining. High explosives detonate, while low explosives deflagrate. Blasting agents, including slow-burning compositions, are used for initiation systems like detonators, detonating relays, and fuse heads. Explosives are classified into four groups: high explosives, low explosives, special explosives, and explosive substitutes.
Air blasting in mining involves using compressed air at high pressure, piped to a steel shell in a shot hole and discharged, creating an air overpressure. Underground mining experiences a rush of air following an explosion caused by factors like rock displacement, ground vibration, gas release, and stemming release pulses. Unconfined surface charges contribute to the most damaging air blast cases.
Solid blasting in mining, used in coal faces, consists of shot holes drilled in a pattern in the coal face, utilizing specific explosives and millisecond delay detonators. The popular wedge-cut pattern involves creating an initial free face by blasting wedge shot holes, followed by enlarging to the gallery size using detonators with lower delay numbers. Fan cut is another shot hole pattern used for solid blasting during development, creating split galleries in pillars. Despite drawbacks such as low coal output and higher explosives consumption, solid blasting offers advantages like low capital costs, operational flexibility, and suitability for steep and dipping coal seams. Delayed blasting of shot holes mitigates roof damage and allows more efficient burden displacement.
