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How are drilling and blasting used to expose a coal seam in surface mining?
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coal mining
Schematic diagram of an underground coal mine, showing surface facilities, access shafts, and room-and-pillar and longwall mining methods.
In surface mining, drilling and blasting are essential unit operations used to break up hard strata (overburden) that cover a coal seam, allowing for its eventual exposure and extraction.12
The Process
- Drilling: Operators drill blastholes into the hard rock layers above the coal. These holes are typically vertical, though horizontal drilling may occur in specific configurations. The holes are arranged in precise patterns defined by the burden (distance to the bench face) and spacing between holes to ensure the desired level of rock fragmentation.13
- Blasting: Once drilled, the holes are charged with explosives, most commonly a mixture of ammonium nitrate and fuel oil, known as ANFO. Specialized trucks often deliver and pump these explosive mixtures into the holes.13
- Fragmentation: The blasting is executed in a controlled sequence to fragment the rock and displace it into a pile. This process clears the overburden, enabling the removal of the blasted material and the subsequent cleaning of the coal seam surface.32