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How is coal recovered from pillars after mine entries have been developed?
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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 room-and-pillar mining, coal recovery from pillars occurs after the initial development phase, during which approximately 30 to 50 percent of the coal is typically extracted.1
The recovery process involves the following considerations and procedures:
- Methodology: The general procedure is to extract one row of pillars at a time. While complete extraction is the ideal objective, partial pillar extraction schemes are more frequently practiced.1
- Pressure Management: As pillars are removed, the resulting increase in pressure must be transferred in an orderly manner to the remaining pillars. This prevents excessive stress accumulation, which could cause unrecovered pillars to fail and endanger personnel or equipment.1
- Subsidence: Once pillars are removed, the mined-out area, known as the gob, is left free to subside.1
- Conditions: The specific methods used for pillar recovery depend heavily on the local roof and floor conditions of the mine.1
Because this process involves significant risks related to roof stability and pressure, it becomes increasingly difficult to practice at depths exceeding 400 to 500 metres.1