Overburden

Overburden is the layer of soil, rock, and organic material that lies above an underlying deposit such as a coal seam or ore body. In surface mining, overburden must be removed to access the ore; the material removed is typically stored as spoil or used for backfilling after extraction. The term can also refer to the cover above other subsurface targets or features, including tunnels, pipelines, or reservoirs.

Overburden commonly includes topsoil, subsoil, weathered rock, clay, silt, sand, and organic matter, and may contain groundwater. Only part of it may be considered waste rock; if it contains small amounts of valuable minerals or chemically reactive minerals, it may be managed separately.

Strip ratio is the amount of overburden that must be removed per unit of ore and is a key economic parameter in open-pit mining. Overburden management also affects slope stability, land disturbance, and potential acid mine drainage.

Environmental and reclamation considerations involve erosion control, sedimentation management, and restoration of vegetation. Reclaimed overburden may be graded and replaced with topsoil to support revegetation, and non-mineralized material can be used as structural fill. Proper handling minimizes long-term environmental impact and aids in post-mining land use.

In petroleum geology and civil engineering, the term overburden can also describe the rock and soil above a buried reservoir or tunnel, influencing hydrostatic pressure, stability, and design considerations.