roomandpillar

Room and pillar is an underground mining method in which a sedimentary or ore body is excavated in a network of in situ rooms while substantial pillars of material are left standing to support the roof. The technique is widely used for relatively flat-lying seams or beds, such as coal, limestone, and some metal ores, where the roof can be safely held by pillars and where extraction equipment can access the rooms.

In a typical room and pillar operation, a mine plan defines a regular grid of rooms separated by corridors and supported by pillars. Excavation proceeds with continuous mining equipment or drill-and-blast methods to create the rooms while leaving pillars in place. Roof stability is maintained with temporary supports, rock bolts, and other ground-control measures. Ventilation and ore transport are organized through the room network. Pillars can be square, rectangular, or irregular in cross-section, and their size and spacing depend on the rock mass, seam thickness, and roof conditions.

There are several variants. Conventional room and pillar leaves pillars throughout the mine to provide long-term support, while retreat mining or pillar extraction gradually removes some pillars in a controlled sequence to recover additional material. This can increase the extraction ratio but also raises the risk of roof collapse and surface subsidence.

Advantages of the method include suitability for thin seams, relatively simple equipment requirements, and good control over ventilation and ground stability. Disadvantages include lower surface subsidence control compared with longwall methods, limits on extraction ratio, and potential for pillar failure if rock conditions change.

Environmental and surface effects, including ground subsidence and potential surface impacts, are central considerations in planning and operating room and pillar mines.