Coal Mining Terms 1

Strata

beds or layers

Goaf

Caved roof materials

At the face

Where the microenvironment is located in a longwall operation

Longwall Mining

It is one of the high extraction methods of mining coal underground

Climate

It is the most important geographical factor influencing coal formation, which affects the rate of floral growth and the degree of preservation of accumulated plant materials in a peat swamp

Tar

It is a liquid, very viscous, hydrocarbon not extractable from oil wells

Kerogene

A solid petroleum that occurs as a component of shale

Pillar extraction and longwalling

The two predominant methods in underground coal mining.

Continuous mining

In room-and-pillar mining, this method is more preferred than the conventional mining method because separate unit operations are eliminated or performed by a single high-performance mining machine. It is also more efficient than the latter, lends more easily to, and benefits from simulation analyses for improving its performance

Pitch Mining

This method is a variation of room-and-pillar mining and is used when the deposit dip exceeds 15 degrees. The necessary modification is to mine cross-pitch to reduce the effective haulage grades.

Air blast

In a longwall mining, it is a sudden and forceful rush of air caused by the violent collapse of the goaf (the mined-out area). This happens when the main roof, usually a strong rock like limestone, remains intact for some time as the face advances (typically 100–150 meters). Eventually, the unsupported roof collapses under its own weight, rapidly compressing the air in the cavity beneath.

Abutment

The solid coal blocks adjacent to the mined-out area. When the roof collapses, the overburden load shifts: some is absorbed by the compacted goaf, while the rest transfers to the _____

Methane Drainage

It is the practice of removing the gas contained in a coal seam and adjoining strata before actual mining through wellbores drill holes, and pipelines

Floor heave

A mode of pillar failure wherein the pillar load exceeds the foundation (floor) material's unconfined compressive strength. The failure is manifested by upward deformation of the floor.

Pillar Scaling

A failure mode where chunks of coal gradually break away from the sides of a pillar due to backpressure and stress. This process slowly reduces the pillar’s size, weakening its structural integrity.

Rock fall

A beam failure mode wherein the roof materials break due to its own weight and presence of natural fractures. The roof debris falls into the opening. However, this is not stress-related

Flexure Failure

A beam failure mode manifested by flexure of the roof under the influence of its own weight plus the weight of the material underneath which is suspended from it by bolting and the weight of softer material overlying it

Tributary Area Theory

The theory that assumes that each pillar carries its full share of the overburden load provided that the width of the panel is as great as or greater than the mining depth and where the mining layout is regular, i.e. where the pillars in a panel are of the same size.

Pillar Run

A large-scale instability involving the failure of a great number of pillars in a partial high extraction system. The massive failure is caused by tremendous pressure transmitted to the pillars by a strong roof

cut+drill+blast+load+haul

The production cycle of operations in the room-and-pillar mining of coal with conventional equipment is modified from the basic cycle by the insertion of cutting to improve breakage.

Simulation

A systematic means of evaluating performance and operational factors for optimizing cycle of operations in conventional mining. This is done usually with the aid of computers

Subsidence

An inevitable outcome from the high-extraction method of mining coal

Easier coal cutting

Effect of high stress on the face

High load transfer

Effect of competent roofs

High stress concentrations

Effect of corners in coal mining

joints striking parallel to the face

Dangerous joints in coal mine

High stress concentration and weak floor

Floor heave is a result of

Easier Coal Cutting

The advantage of a strong roof in longwalling is

High stress concentration at the face

Disadvantage of a strong roof in longwalling is

It begins to destabilize

When the goaf has fully developed, the extraction panel

Increases

As the face advances, stress acting on it

The stresses are redistributed

When the roof caves in longwalling

Roof is weak

Violent caving of the roof happens when

Floor is weak and roof is strong

Floor heaving happens when the

Structures present in the pillar

The strength of a coal pillar is dependent upon the strength of the coal material and

Barrier Pillars

Large pillars in a coal mine to protect smaller onesBu

Bump

Failure of a coal pillar by overstress

Longwall mining

The coal mining method that best control coal bumps

Pressure Arch Theory

The theory which implies that upon excavation of an opening in a coal seam, the redistributed stress forms an elliptical arch