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      Adit (or incline): A walkable outlet from the mine workings to the surface. Or, a passage for drainage or access, driven at a shallow angle (usually below the horizontal) often in a hillside. Also known as ‘drift’ particular when driven as a major access from a level ground surface (also termed ‘slough’ or ‘sough’).

      Angle-of-draw (limit angle): The angle of inclination from the vertical of the line connecting the edge of the workings and the edge of the subsidence area.

      Barrier: Coal or rock left unworked to keep workings separate or to give protection form a natural hazard (like groundwater).

·         Backfill: (a) Material used to fill the void following the extraction of the mineral. (b) Overburden replaced after the opencast extraction of the mineral. (c) Loose material placed behind the shaft wall or the lining of any other excavation.

·         Bed separation: The moving apart of bedding planes caused by mining subsidence.

·         Bulking: (a) Process of increasing in volume of a mineral or rock when mined and stored. (b) Ground which has collapsed into a void.

·         Cap: A strong slab or block of concrete placed over a shaft and capable of supporting the weight of any ground above it and a specified superimposed load.

·         Caving. The process of permitting the roof or hangingwall into the space from which coal or mineral has been excavated.

·         Cover: A timber, steel or concrete platform placed over a shaft at the surface.

·         Convergence: Movement of roof and floor towards each other after the extraction of the mineral.

·         Critical area: That area the workings of which causes the complete subsidence of one point on the surface.

·         Crown hole: (a) Surface cavity created by the collapse of soil into mine workings. (B) solution formed void.

·         Dam: A roadway stopping capable of supporting a saturated fill extending to ground level without significant leakage through either the dam or the surrounding rock.

·         Discontinuity: Fracture or break in soil or rock (such as a joint, bedding plane or subsidence induced fracture).

·         Differential settlement: The difference in settlement between any two points on a foundation or loaded area of soil.

·         Drift: see ‘adit’.

·         Drift mining: Mining along a mineral body from ground surface, at a shallow angle usually along the dip of the strata.

·         Displacement: (The horizontal displacement of a point caused by any workings).

·         Enclosure: A fence, wall or building designed to prevent unauthorised access directly to a shaft or adit.

·         Face: Any surface exposed by excavation or for the purpose of extracting coal.

·         Fall: Loose material (rock or soil) which has fallen from the roof or sides of an excavation.

·         Fault: A discontinuity in rock (sometimes soil) where there has been observable and measurable relative displacement.

·         Fill: (a) Soil, rock or waste material placed in a shaft to occupy voids. (b) Soil, rock or waste material placed to fill or to raise the surface elevation or to provide a more stable base. (c) Structural fill refers to material placed and compacted in layers under careful and controlled conditions to achieve a uniform and dense mass capable of supporting structural loading.

·         Gallery: A void left behind following the extraction of a large mass or rock or mineral, often mined in a vertical direction (known also as chamber).

·         Gangue: Minerals of no value (waste) from a mineral vein.

·         Goaf: The caved area where coal (or mineral) has been worked.

·         Gob: Synonymous with ‘goaf’ (sometimes applied to metalliferous mines).

·         Ground investigation: Exploratory investigation to determine the structure and characteristics of the ground influenced by a development or mining operation. The established information is used to predict, for example, the characteristics of the ground, groundwater behaviour and geohazards during, and subsequent to construction and/or mining.

·         Groundwater: Aqueous liquid present in soils and rocks.

·         Groundwater level: The subsurface elevation(s) at which water is usually present.

·         Grout acceptance: The quantity or rate of grout consumption (injected into the ground).

·         Hydraulic fill: Grout moved and placed by water.

·         Limit angle: Known also as ‘Angle-of Draw’, the angle of inclination of a line connecting the edges of the workings and the edges of the observable subsidence, measured from the normal to the seam.

·         Longitudinal subsidence profile: A curve depicting subsidence on a vertical section drawn parallel to the direction of advance of an underground excavation.

·         Longwall mining: A method for the total extraction of a coal seam along a longwall face. Usually about 200 m wide and may be several hundreds of metres long.

·         Mining: The process of extraction or abstraction of mineral deposits from either the surface of the Earth or from beneath the surface.

·         Mining consolidation: Remedial measures to increase competence of collapsed workings or to infill voids associated with mining.

·         Mining investigation: That part of a site investigation which explores the ground to determine the type, extent, and condition of old mine workings, shafts and/or adits and their effects with respect to existing or potential new developments. In some circumstances and investigation may be carried out to assess the effects of an existing or proposed structure from existing or proposed mining.

·         Offset: Mine roadways that extend laterally outwards from a shaft. These may be at different stratigraphic levels.

·         Panel: The area of coal extracted by a longwall face.

·         Pillar: A block of coal left unworked (known also as bord or stall).

·         Plug: A substantial block of concrete in a shaft keyed into the surrounding rock or into a roadway connecting with the shaft. A plug must be capable of supporting a saturated fill extending to the surface.

·         Profile: A curve depicting subsidence on a section drawn at right angles to the direction of advance of an underground excavation.

·         Pneumatic stowing: The filling or partial filling of the goaf with waste material transported through pipes by compressed air.

·         Prop: An individual straight support member set between the rook and floor of the mine.

·         Settlement: (a) The amount of downward vertical movement of the foundation of a structure, under conditions of applied load. (b) The downward vertical movement experienced by structures or a soil surface as the underlying supporting ground compresses.

·         Shaft: Vertical or near vertical opening used for access, removal of minerals or ventilation of a mine.

·         Shaft diameter: The largest plan dimension of a shaft whether the shape be circular (as is most usual), rectangular or oval.

·         Site investigation: Comprehensive investigation of a site, including past land use and environmental constraints, to determine its suitability for development and to provide information which leads to safe, economic and practical design of structures.

·         Slope: The slope of any part of the subsidence trough.

·         Staple shaft: Shaft connecting two or more offsets, but not connecting those to the ground surface.

·         Stope mining: Mining method adopted for extensive mineral extraction where collapse of the mine roof is induced and the mineral is collected at lower levels through rock funnels.

·         Stopping: Partition constructed across underground access road or mine goaf, usually to cut off old mine workings or direct ventilation.

·         Strain: Change in length per unit of length.

·         Stopping: A permeable obstacle constructed in a mine roadway and designed to retain fill material in an abandoned shaft with which the roadway connects.

·         Sub-critical area: An area of workings smaller than the critical area. (When a sub-critical area is being worked, the point on the surface under investigation does not undergo complete subsidence).

·         Super critical area: An area of working greater than a critical. (An area on the surface undergoes complete subsidence).

·         Subsidence: (a) The term subsidence as applied to the Earth’s surface normally refers to a point sinking to a lower level. (b) This term also commonly refers to en mass lowering of the ground rather than localised effect of consolidation or shrinkage of soils. (c) In a coal mining context this may be regarded as the downward vertical movement of the ground anywhere within a subsidence trough as a result of processes independent of the loads applied. (d) Movement of the ground caused by loss of support over mine workings. Subsidence is a three dimensional process involving rotations, and translations with the ground and often gives rise to differential vertical movements and horizontal strains of the ground surface.

·         Subsidence (maximum): The maximum vertical movement caused by working a sub-critical area.

·         Subsidence (maximum possible): The maximum possible vertical movement caused by working a sub-critical area. (This corresponds, in general, to the seam thickness, multiplied by the subsidence factor).

·         Subsidence factor: The ratio of complete subsidence to seam thickness.

·         Subsidence development: The manner in which surface subsidence starts increases and finishes in relation to the position of the advancing face of an underground excavation.

·         Subsidence development curve: A line on a graph depicting subsidence of a surface point in relation to the position of the face of an excavation passing through the critical area of that point.

·         Subsidence wave: The line on the ground surface along which the initial subsidence progresses.

·         Trough: The surface depression caused by subsidence.

Subsidence Index | Coal Mining Index |  Diagnostic Characteristics | Geographic Occurrence | Investigation & Mitigation | Key Contacts & Expert Advice | Photo Gallery | Essential References & Further Reading |  Definitions & Glossary |