Coal Mining
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.
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.
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.
bolt
A coal mining support (post, bolt, peg, stake)
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.
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
kerogene
A solid petroleum that occurs as a component of shale.
face break
A sudden spalling or collapse of the coalface caused by stress concentration at the face resulting from goaf hang-ups and presence of joints near and parallel to the surface. This happens under strong roof and floor conditions.
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
abutment
After the collapse as in air blast, a redistribution of the overburden pressure occurs. Part of the load now rests on the goaf and the remainder is partly carried by the
subsidence
An inevitable outcome from the high-extraction method of mining coal
pillar scaling
Another pillar failure mode wherein the coals pillar, due to backpressure, gradually scales off. This effective reduces the size of the pillar, thereby reducing its strength and increasing the pillar stress.
increases
As the face advances, stress acting on it (increases, decreases, fluctuates, will not change)
joints striking parallel to the face
Dangerous joints
high stress concentration at the face
Disadvantage of a strong roof in longwalling is
high load transfer
Effect of competent roofs
high stress concentrations
Effect of corners in coal mining
easier coal cutting
Effect of high stress on the face.
bump
Failure of a coal pillar by overstress.
high stress concentration and weak floor
Floor heave is a result of
floor is weak and roof is strong
Floor heaving happens when the
caved roof materials
Goaf means (in-situ rock, caved roof materials, coal refuse, powdered coal)
there is a high concentration at the face
If the coal is easy to cut
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.
tar
It is a liquid, very viscous, hydrocarbon not extractable from oil wells
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.
barrier pillars
Large pillars in a coal mine to protect smaller ones.
beds or layers
Strata means (beds or layers, beams or bars, coal seams, surrounding rocks)
easier coal cutting
The advantage of a strong roof in longwalling is
longwall mining
The coal mining method that best control coal bumps.
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.
structures present in the pillar
The strength of a coal pillar is dependent upon the strength of the coal material and (height of pillar, width of pillar, structures present in the pillar, load imposed on the pillar)
no answer
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.
pressure arch theory
The theory which implies that upon excavation of an opening in a coal seam, the redistributed stress forms an elliptical arch.
pillar extraction and longwalling
The two predominant methods in underground coal mining.
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
This phenomenon in longwall mining is a result brought about by the violent collapse of the goafs compressing the cavity underneath the main roof. The occurs when the roof is competent (e.g. a massive limestone) and the face has advanced for a distance of 100 - 150m.
roof is strong
Violent caving of the roof happens when the
it begins to destabilize/is finally stable
When the goaf has fully developed, the extraction panel
the stresses are redistributed
When the roof caves in longwalling
at the face
Where the microenvironment is located in a longwall operation. (at the face, at the roof, at the floor, in the entire panel)
