Retreat mining
Retreat mining is a term used to reference the final phase of an underground mining
Mining is the extraction of valuable minerals or other geological materials from the earth, from an ore body, vein or seam. The term also includes the removal of soil. Materials recovered by mining include base metals, precious metals, iron, uranium, coal, diamonds, limestone, oil shale, rock...

 technique known as room and pillar
Room and pillar
Room and pillar is a mining system in which the mined material is extracted across a horizontal plane while leaving "pillars" of untouched material to support the roof overburden leaving open areas or "rooms" underground...

 mining. This involves excavating a room or chamber while leaving behind pillars of material for support. This excavation is carried out in a pattern advancing away from the entrance of a mine. Once a deposit has been exhausted using this method, the pillars that were left behind initially are removed, or 'pulled', retreating back towards the mine's entrance. After the pillars are removed, the roof (or back) is allowed to collapse behind the mining area. Pillar removal must occur in a very precise order in order to reduce the risks to workers, due to the high stresses placed on the remaining pillars by the abutment stresses of the caving ground.

Retreat mining is the term commonly referred to as the mining method employed by the Crandall Canyon Mine
Crandall Canyon Mine
The Crandall Canyon Mine, formerly Genwal Mine, was an underground bituminous coal mine in northwestern Emery County, Utah.The mine made headline news when six miners were trapped by a collapse in August 2007. Ten days later, three rescue workers were killed by a subsequent collapse...

 and is believed, by some, to be a factor in the August 2007 collapse which trapped six miners. On November 21, 2007, the mine was sealed, entombing the deceased miners. The bureau of land management says retreat mining was being used. Robert E. Murray
Robert E. Murray
Robert E. Murray is an American CEO of Murray Energy Corporation, a mining corporation based in Pepper Pike, Ohio, near Cleveland. He is one of the largest independent operators of coal mines in the United States.-Personal details:...

, CEO of Murray Energy (owner of the mine) says the technique was not being used at Crandall Canyon.

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