Glossary - Coal Waste Impoundments: Risks, Responses, and Alternatives - page 198

BLOW-OUTOpposite of blow-in; catastrophic failure resulting from build-up of
underground water pressure against an outcrop coal barrier. Material
“blows out” from underground workings to the surface.

BONY
COAL

Coal high in mineral content, usually clay shale particles.

BREAK-
THROUGH

Catastrophic failure/opening of mine working along a fracture, joint,
bedding plane, or other zone of weakness.

BTU
(BRITISH
THERMAL
UNIT)

Heating value for a unit weight of coal. The heat needed to raise one pound
of water one degree Fahrenheit.

BULK-
HEAD

A seal constructed to prevent water from entering or exiting an area of the
mine. Barrier design and construction is based upon the amount of water
pressure (water head, expressed in feet) that will be exerted against the
bulkhead.

CLOSED-
LOOP
SURVEY

Method of establishing the accuracy of a mine survey by conducting a loop
traverse to the point of beginning. The accuracy is measured in terms of a
ratio of feet of error to feet of traverse, e.g., 1:5000 indicates an error of 1
foot over a 5000-foot traverse.

COMPRES-
SIVE
STRESS

Stress that pushes together material on opposite sides of a real or imaginary
plane.

CON-
TROLLED
PLACE-
MENT

(as used in this report) Injection of coal waste slurry into an underground
mine that has been mapped and inspected, whose volume is known, and in
which bulkheads may be built to control the direction and extent of flow.

DAM An artificial barrier or wall constructed across a watercourse to confine

flowing water for a variety of purposes, such as creating a pond or lake for
storage of water; creating a hydraulic head that can used to generate power;
controlling floods; or retention of debris.

DEPTH-TO-
MINED-
HEIGHT
RATIO

Ratio of the depth of the coal seam to the mined-height, or “effective
thickness,” of the mined seam.

DOWN-
STREAM
CON-
STRUCTION
EMBANK-
MENT

A method of staged embankment construction where the embankment
centerline is moved downstream with subsequent embankment raises.

EMBANK-
MENT

(as used in this report) A linear engineered structure extending above the
natural ground surface that retains fine coal slurry waste material; it is built
with earthen materials or coarse coal refuse (waste material).

EXTEN-
SOMETER

An instrument for measuring changes caused by stress in a linear dimension
of a body.

FACTOR
OF SAFETY

A quantitative measure of the ratio of available strength to applied force.
For slope stability, factor of safety is the ratio of forces resisting slope
movement to forces causing slope movement.