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Why are coal pillars left behind in room-and-pillar mines?

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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 pillars are left behind primarily to provide structural support for the overhead strata of earth and rock. By creating a grid formation of these pillars, miners can maintain the stability of the mine's entries and prevent the collapse of the roof.123

These pillars are essential for ensuring the safety of workers and equipment by managing the pressure exerted by the overlying layers. While these pillars are left in place during the initial development of the mine, some or all of them may be extracted later—often starting from the boundary of the deposit—once the primary mining phase is complete. When pillars are removed, the process must be carefully managed to transfer the increased pressure to the remaining pillars, preventing failure and allowing the mined-out area to subside in a controlled manner. Additionally, leaving large, undisturbed blocks of coal can help reduce subsidence on the surface.123