2012-05-11_PERMIT FILE - C1981033 ‎(3)‎

• Permit No: C1981033
• IBM Index Class Name: Permit File
• Doc Date: 5/11/2012
• Section_Exhibit Name: Rule 2.05 Operation and Reclamation Plans
• Media Type: D
• Archive: No

2.05.6(6)
report reviewed the B -Seam mine plan. Its main purpose was to
predict the magnitude of subsidence expected from the B -Seam mine
plan in combination with the mining that had already occurred in
the C -Seam.
Underground mining frequently results in measurable rock response
remote from where the mining takes place. Shallow room and pillar
mining can breach the ground surface through the collapse of rock
above mine openings. This type of progressive upward collapse of
rock above an extraction is generally called chimney collapse,
Figure 7. The collapse chimney is generally centered over an
individual intersection or opening. When pillars fail or crush out
in room and pillar mining, the overlying and adjacent strata
deflect downward and laterally toward the area of extraction and
pillar failure. This is generally referred to as trough
subsidence, Figure 8. The deflection subjects the overlying strata
to compressive strain over the center of the extraction area and to
tensile strain adjacent to the extraction area. The subsidence
trough can extend well outside of the area of extraction and pillar
failure.
• Excavation of mains, sub - mains, and advance rooms in the mine under
less than 110 feet of overburden has the potential to produce the
chimney collapse type of subsidence. The chimneys that may form if
the mine workings are not supported will progress upward over time,
until the natural expansion of the collapsed roof rock fills the
individual mine opening and plugs the collapse chimney. When
chimney subsidence breaches the surface it is usually noticeable.
The potential adverse surface effects caused by chimney subsidence
are greater at this site opposed to the potential effects caused by
trough subsidence. Robbing of pillars during retreat from planned
panels would be anticipated to produce pillar failure and,
therefore, trough subsidence within the overlying strata.
Controlled pillar failure during retreat from a panel is preferred
to pillar failure occurring at some unknown time in the future.
Trough subsidence can all be residual, taking place long after
mining in the critical area has been completed. Subsidence of the
surface over room - and - pillar workings, that occurs when pillars
fail, depends on when and how the pillars fail. The time period
will be extremely short if all the pillars fail suddenly. On the
other hand, the gradual failure of pillars in an abandoned room-
and-pillar panel will result in the equally gradual subsidence of
2.05 -58 Rev. 11 -30 -93