longwall

Longwall mining is an underground coal mining method in which a long wall of coal, typically hundreds of meters wide and several kilometers long, is mined in a single continuous operation from a panel. The method uses hydraulically powered roof supports, called shields, to retain the roof as the coal is cut from the face by a machine such as a shearer. The mined-out area forms a goaf behind the advancing face, and coal is transported to the surface via an armored face conveyor and belt system.

Key equipment includes an armored face conveyor (AFC), a shearer or plow, shield supports, and a belt conveyor network. After a panel is prepared, shields are erected to form a stable roof along the face. The shearer cuts coal as the face advances, and the coal is loaded onto the AFC and carried to surface. In retreat longwall mining, the face moves away from the intake, with the shield line and conveyors following until extraction is complete.

Advantages include high productivity, efficient coal recovery, and reduced need for development entries compared with room-and-pillar methods. Longwall can operate continuously, but it requires substantial capital, skilled ventilation and methane management, and strict roof control to prevent collapses.

Environmental and safety considerations include surface subsidence above mined panels, which can affect structures and hydrology, and the need to manage methane and dust through ventilation, gas drainage, and suppression systems.

Longwall mining emerged in the 20th century and is now a dominant method in many coal regions with thick seams. It is primarily used for coal, though related techniques exist for other minerals. It is contrasted with room-and-pillar mining, which extracts coal in multiple rooms with pillars left to support the roof.