goaf

A goaf is a term used in mining to describe the void left behind after ore or coal has been extracted from a mine working. The space, which may include collapsed roof and broken rock, can extend behind the active face and beneath or around the completed sections of mine workings. The term is commonly used in British and other Commonwealth mining contexts, and it can refer to both the empty cavity itself and the surrounding collapsed or backfilled material.

In formation, a goaf develops as extraction proceeds, especially in longwall and room-and-pillar mining. As ore or coal is removed, supporting structures may fail and the roof may cave, creating a network of voids filled with broken rock. If the goaf is later backfilled with waste rock or other fill material, it becomes a backfilled goaf; if it remains unfilled, it may remain as an empty or partially caved space, potentially permeated by air or water.

Goafs present several hazards. Subsidence can affect surface structures and ecosystems, while trapped gases such as methane can pose explosion risks. Water inflow can lead to flooding, and long-term deformation can impact groundwater flow. Because of these risks, goafs are typically monitored and managed through geological studies, ground control practices, drainage, and, in some cases, backfilling or grouting to stabilize the void and mitigate subsidence.

The concept is primarily of interest in coal and metal mining operations, where understanding goaf geometry and behavior is important for mine safety, ground stability, and groundwater management.