Assertion: retreat mining | /r/HasProperty | method
Facets:
Source sentences:
text: Vertical retreat mining (VRM) also known as Vertical crater retreat (VCR) is a method where mine is divided in vertical zones[ clarification needed ] with depth of about 50 meters using open stoping, bottom-up mining.
text: Retreat mining is a method in which the pillars or coal ribs used to hold up the mine roof are extracted; allowing the mine roof to collapse as the mining works back towards the entrance.