PERMFILE100116

• Permit No: C1981038
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: VOLUME 2 MINE PLANNING APPENDIX - PILLAR STABILITY
• Media Type: D
• Archive: No

OUTCROP BARRIER STUDY
Purpose of Stud Y:
The purpose of this study is to:
1. describe previous mining around the burnline and outcrop barrier
pillar,
2. set future outcrop barrier sizes,
3. describe future monitoring and control procedures during develop-
ment mining of outcrop barriers both underground and on the sur-
face, and
4, describe procedures for modifying the outcrop barrier design.
Previous Mini
Previous mining is shown on Maps 2-4 and 2-5. On these maps, the outcrop
for the "D" seam and the burnline are also shown. CWI has mined in the
vicinity of burnlines in sections designated 1 West, 1 East, 2 East, 8E-25,
5E-15. Typically, the sections have been developed to the burnline as shown
on the drawinys. Rased on the location of the outcrop and this burnline,
the distance varies from 300 to 1000 ft.
The mininy conditions experienced in those sections were as follows. As in
the entire permit area, the "D" seam dips to the north. Under clay litholo-
gies are not common as floor strata, although present in isolated locali-
ties. The burnline is not the interface between altered and unaltered coal,
but a zone where indication of oxidation is evident (limonite staining,
• fractured strata, etc.) AS the burnline was approached, the roof condi-
tions did not change. Also, the floor conditions and ribs indicating pillar
stability did not change. Finally, no groundwater changes were experienced,
In 8E-15 section, CWI mined past the burnline for approximately 100 ft., and
again there were no apparent changes in roof conditions, floor conditions,
stability, or groundwater. Upon retreat mining in this section, no evidence
of barrier pillar failure was indicated. No unusual stress relief evidenced
by bumping occurred, Areas around the outcrop and burn are typically under
low overburden and stresses are relatively low,
CWI has not mined past the burn and into altered coal areas. No observa-
tions or strength of this material can be ascertained.
Outcrop Barrier Desion:
CWI chose to be conservative in designing of outcrop barrier pillars and
give no stability strenyth to the altered coal areas. Because no tests
could be made on this materiai, it was deemed most conservative Lo not give
it any support characteristics.
Because of the low overburden depths around the burnline and outcrop, pillar
stability Calculations show a high factor of safety of approximately 4,
using Wilson's formulas for a 50 ft. wide pillar. See calculations
attached.
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