Glossary for mining subsidence

 

This glossary contains terms found in this report and common terms that are found in publications and subsidence investigations. These definitions have been adapted from the Dictionary of Mining, Mineral and Related Terms.

Abandoned Workings — Mined excavations that are deserted and in which further mining is not intended.

Adit — A horizontal or nearly horizontal passage driven from the surface for the working or dewatering of a mine.

Backfill — In general refers to material placed to refill voids left after mining.

Barrier pillar — A solid block or rib of coal left unworked between two adjacent mines.

Bentonite — material composed mostly of the clay mineral montmorillonite. This rock has great ability to absorb water and swell.

Bituminous — A subclass of coal, high in carbonaceous matter.

Chimney — A pipe-like, more or less vertical, vent or opening in the earth.

Cleat — The main joint(s) in a coal seam along which it breaks most easily.

Coal — Solid, brittle, combustible rock composed of at least 50% (by weight) of carbon; formed from altered plant remains and classified by plant material(type), impurities (grade) and degree of metamorphism (rank).

Compression — The stress that tends to compress material, or shorten its length.

Crownhole — A bell-shaped hole at the surface caused by subsidence.

Depositional Environment — The sum total of all external conditions acting on the natural accumulation of rock forming material.

Drift — Applied to coal mining, an entry on the slope of a hill, driven horizontally into the coal seam.

Drilled piers — A circular column formed by a drilled hole, usually filled with concrete, used to support concentrated loads.

Entry – An opening or set of openings driven in coal for the purpose of developing a mining section.

Fault — A break in a mass of rock along which there has been movement parallel to the fracture.

Helical Pier — A steel tube or rod with helical flights (threads) that is screwed into soil or soft rock to form a support for foundation loads.

Haulageway — The entry or tunnel through which mine cars are hauled in and out of the mine.

Joint — Fractures in rock along which no appreciable movement has occurred.

Lignite — A soft, brownish-black coal of low rank and grade. (see coal)

Longwall Mining — A mining technique where the coal seam is removed in one continuous operation by means of a long working face or wall. The workings advance in a continuous panel which may be several hundred yards in length.

Mudstone — A rock made up of clay and silt sized particles.

Overburden — Material of any nature (rock or soil) that overlies a deposit of ore or coal.

Piping — The action of moving groundwater removing small soil/rock particles and creating new void space.

Potholes — A circular or funnel-shaped depression at the surface, caused by subsidence.

Pull Pillars — To remove the coal pillars.

Rob — To extract coal (or ore) previously left for support, to remove pillars without regard to maintaining the mine workings. Also used where coal is removed illegally from beyond property boundaries.

Room and Pillar — A system of mining in which the coal is mined in rooms separated by narrow pillars.

Sandstone — A rock consisting of cemented or compacted sand-sized grains. These grains are commonly, but not always, composed of quartz.

Section — The working area in a coal mine operated by one crew of men.

Shaft — A vertical (or near vertical) excavation made for ventilation and hoisting equipment and personnel from underground workings. A mine will most often have two or more shafts.

Shale — A fissile , platy rock made up of clay-sized particles.

Siltstone — A rock made up of silt-sized particles.

Slope — An inclined tunnel driven from the ground surface to a coal bed or seam.

Strain — The change in length per unit length in a given direction. See Tension and Compression.

Stoping — upward propagation of subsidence along a dipping mined-out seam.

Subsidence — The lowering of the strata, including the surface, due to underground excavations, withdrawal of fluid, or loss of strength in the supporting material.

Swelling Soils — Clay soils that have the capability to expand when wetted. These soils may contain bentonite. Bedrock composed of clay can also swell.

Tension — A force tending to produce elongation or extension.

Tilt — The change in surface slope of a part of a subsidence trough.

Working Face — The place where the coal is actively being removed from the seam.