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

• 2.0 METHODOLOGY
This section describes the pillar design methods utilized in this
study, the model calibration methods, and the determination of
the minimum required factor of safety for pillars.
2.1 Pillar Design Methods
The confined core pillar design method of A. H. Wilson is used to
evaluate pillar stability. Wilson {1972) originally published
the method. Wilson subsequently expanded the method to include
the effects of yield in the roof and floor strata adjacent to a
pillar. Wilson (1977, 1981, 1982a, and 1982b) describes this
modified method.
Wilson's method differentiates between a rigid rock mass model
and a yield rock mass model. The yield model is characterized by
yield in the roof, pillar, and floor. The rigid model restricts
yield to the pillar while the roof and floor remain rigid.
The yield model was selected as the most representative rock mass
model for the proposed mining in the Steven's Gulch area of
Panel B at the Orchard Valley Mine. Mining in this area will
occur within the coal seam, leaving roof and floor coal. The
immediate roof and floor rocks are classified as moderately weak
• silty shale.
Wilson's method requires physical rock property data for the coal
seam and overburden density. The Table 1 summarizes the required
data and the design values used in the pillar stability analyses.
These data were developed from existing test data from the East
Mine area. Figure 1 summarizes the results of the test data
analysis.
Table 1
Physical Properties Data
Panel B Pillar Stability Analyses
Parameter Desi n Value
Maximum overburden de th 800 ft
Overburden densit 160 lb ft^3
Laborator com ression stren th 5681 si
Insitu stren th reduction factor 5
Internal an le of friction 40.2 de
•
Cyprus Orchard Valley Mine February 6, 7992
Panel B Pillar Analysis page 2