2009-09-21_PERMIT FILE - C1980007 ‎(2)‎

• Permit No: C1980007
• IBM Index Class Name: Permit File
• Doc Date: 9/21/2009
• Section_Exhibit Name: Exhibit 51 Lower Refuse Pile
• Media Type: D
• Archive: No

Mountain Coal Company, L.L.C. Exhibit 51
West Elk Mine Lower Refuse Pile
The stability of the LRP, during an earthquake event, was also investigated using an assumed maximum
horizontal and vertical ground acceleration of 0.1 g (earthquake loading factors). The minimum
pseudostatic factor of safety analysis was found to be 1.26 for Profile 3. Critical failure circles and their
associated factors of safety can be found in Appendix K. The complete results of the entire slope stability
analysis can be found in Table 9.0.
Table S. Summary of Stability Analysis Results Factors of Safety (F.S.)
Profile: Percentage Fines'
Static: Factor of Safety
Pseudostatic: Earthquake F.S.
Profile 1: 7.6 %
2.52
1.89
10%
1.67
1.30
20%
2.28
1.72
30%
2.54
1.90
Profile 2: 7.6 %
2.23
1.76
10%
1.63
1.27
20%
1.96
1.54
30%
2.24
1.77
Profile 3: 7.6 %
2.65
2.14
10%
1.63
1.26
20%
2.22
1.77
30%
2.68
2.17
1. Percentage fines represents the amount of coal, as a percentage of the total amount of coal, that has
passed the #200 sieve.
The stability analysis results indicated that no keyway was required for the Phase V reconfiguration;
however, two keyways were cut along the north and east perimeters to properly connect the existing refuse
fill with Phase V fill. The keyways were located: 1) along the base of the existing north and east faces of
the LRP, and 2) along the existing bench which extends around the north and east faces at the 6230 -feet
contour. Keyways were cut with 2H:1 V sideslopes to a minimum relative depth of 2 -feet and had a
minimum width of 10 -feet. The keyway along the existing bench was offset from the outside edge a
minimum of 10 -feet.
An additional stability analysis was completed in September 2009 (per TRl 18) to determine if the loading
resulting from the construction of the Coal Preparation Plant and associated facilities atop the LRP would
affect the stability. The analysis resulted in a factor of safety greater than 1.5 indicating that the LRP would
remain stable. A copy of this analysis is included at the end of Exhibit 51.
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