wicket

In pillar-and-stall (or room-and-pillar) mining, a wicket is the open space driven between two load-bearing pillars left standing in the seam. The pillars themselves are rectangular blocks of unmined coal or ore, typically 15 to 30 meters wide depending on depth and roof condition. The wicket is the worked-out corridor connecting one pillar group to another, allowing extraction to continue and access for haulage and ventilation.

The term appears to derive from the resemblance to a wicket gate: just as a gate frames an opening in a fence, the wicket frames the open space framed by pillars on either side. In practice, wickets are driven perpendicular or parallel to the main extraction direction. Their width must balance extraction efficiency against roof stability; too narrow and ore yield falls, too wide and pillar load increases dangerously.

Roof support and geometry

Wicket width is constrained by the span the roof can safely carry unsupported. In shallow seams with strong overburden, wickets may reach 8 to 12 meters across. In deeper workings with poorer roof conditions, widths may be limited to 4 to 6 meters. The pillars flanking each wicket share the weight: wider wickets force taller, wider pillars, consuming more of the seam as coal. Conversely, narrow pillars need closer spacing, which means more wickets to extract the same block.

Roof falls and pillar squeeze are the chief hazards at wicket boundaries. As mining advances and stress redistributes, pillars near active wickets carry elevated load. Bump (sudden pillar failure) is a risk in deep, high-stress mines. Systematic monitoring of pillar convergence, sometimes by surveying or radar, helps predict instability before failure. Propping or crib supports are occasionally installed in wider wickets as extra insurance.

Wicket geometry also affects ventilation distribution. Air must flow through wickets to reach the working face; badly designed wicket layouts can create dead zones where firedamp or dust accumulate. Mine planning therefore treats wicket spacing and orientation as part of the overall ventilation circuit, not merely as a byproduct of pillar geometry.