shearing

In coal mining, shearing is the controlled vertical cut made into the coal face to create a clean edge from which extraction can proceed. The shear produces a vertical wall of exposed coal, typically 1.5 to 3 meters in height, and stands as the primary working surface for the next phase of mining. This cut is fundamental to room-and-pillar mining systems, where coal is extracted in blocks separated by supporting pillars of unmined coal.

The cut is made using a coal shearer, a machine equipped with a rotating drum or chain fitted with cutting picks. The shearer advances horizontally along the coal face while cutting downward, or in some cases, advances vertically while cutting horizontally, depending on the machine design and seam geometry. The resulting void, called the shear or shear cut, is typically 0.5 to 1 meter wide and provides access to the uncut coal mass beyond it. Modern automated shearers can work faces up to 3.5 meters high in a single pass.

Shearing differs from undercutting or other preparatory cuts because of its emphasis on creating a vertical working surface rather than a horizontal one. The vertical orientation of the shear cut makes it particularly suited to seams of moderate to substantial thickness and is less suitable where coal is very thin or highly fractured. Rock quality, coal hardness, and moisture content all affect cutting speed and tool wear during shearing operations.

The term reflects its function: the shearer shears through the coal face as a blade shears through material, producing a clean geometric separation. In older systems, shearing was done with hand tools or compressed-air picks, a labor-intensive process; modern shearer drums cut at rates of several cubic meters per shift. The shear cut also serves a safety function by isolating loose or unstable coal in the unmined block, allowing miners to work in a more controlled geometry.

Shearing sits within the broader sequence of coal extraction: after geological surveying and roof support installation, shearing prepares the face; drilling and blasting or further mechanical extraction then follow. In longwall mining systems, which dominate modern large-scale operations, shearing has been partially superseded by shearer drums that work continuously along the coal seam, but the principle of vertical face cutting remains central to the operation.