Pull mining proceeds away from the mine entrance and then back forward.
Retreat mining is the last phase of a common type of coal mining technique known as room and pillar mining. In room and pillar mining, a mining machine known as a “continuous miner” drills a network of chambers or “rooms” into a coal seam, leaving behind an unexcavated pillar of coal in each room to support the roof of the mine . . Room and pillar mining progresses inward, away from the mine entrance. When the coal seam is depleted or the mine property boundary is reached, pullout mining is a process that reclaims the supporting coal pillars by working from the rear of the mine towards the entrance, hence the word “withdrawal”.
Coal mining is known as a dangerous and dirty profession.
Room and pillar mining leaves behind approximately 57% of the coal in the mine for support. This represents a strong financial incentive for retreat mining as a way to recover more material and maximize profits. However, retreat mining is a dangerous operation, guided by strict safety regulations.
By pulling up support pillars, various techniques are used to prop up mine roofs and prevent them from collapsing. Movable roof supports relieve pressure on adjacent pillars during this precision-driven extraction phase. In some cases, wooden cradles or hydraulic jacks are fixed. Working from the rear of the mine towards the entrance, roof collapses are expected as a result of the mining withdrawal, although the collapsed portions should already be mined and vacated.
Retreat mining is the last phase of the chamber and pillar technique used by coal miners.
One of the dangers associated with back mining is coal blasting. As the stabilizer pillars are removed, pressure builds on the remaining walls and pillars. Just as a stick breaks when enough pressure is applied, pressure can build to the point where a wall or pillar explodes, throwing material down the mine. The result can be lethal to nearby miners and can be complicated by localized roof falls. A massive collapse of one pier can also trigger a domino effect on adjacent piers, leading to catastrophic failure.
Extractive mining made headlines in August 2007 when six miners were stranded at Utah’s Crandall Canyon mine. The miners were trapped at the rear of the mine on August 6 in a cave-in that generated a seismic reading of 3.9 to 4.0 recorded in Nevada. In the rescue attempt that followed, a secondary collapse occurred ten days later, killing three and injuring six. The original miners were never found and rescue operations were canceled due to security concerns. Although retreat mining was carried out on parts of the mine, co-owner Robert E. Murray publicly stated that it was not taking place at the time of the collapse.
In the United States, the US Department of Labor’s Mine Safety and Health Administration (MSHA) is responsible for regulating mining operations, including retreat mining. Research to improve mine safety is ongoing.