Retreat mining

In the first phase of room and pillar mining, tunnels are advanced into the coal or ore body in a rectangular pattern resembling city streets.

As the pillars are removed, the mine collapses because nothing remains to support the roof and overburden.

Removing pillars causes stresses within the mine to shift and must be planned and executed carefully to reduce danger to miners and control the amount of stress exerted on remaining pillars and the mine floor.

Tunnels only make up about 15% of the reserve, so during advance mining, only about 15% of the coal or ore is removed.

During retreat mining, an additional 75% of coal or ore may be removed because pillars make up much more of the reserve, bringing the total recovery of the resource to as much as 90%.