PERMFILE47451

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: Exhibit 51 Lower Refuse Pile
• Media Type: D
• Archive: Yes

Mountain Coal Company, L.L.C. Exhibit 51
West Elk Mine ~ Lower Refuse Pile
• 5.6.3 Analyses Results
The slope stability sensitivity-style analyses were conducted on twenty-four LRP profiles (Figure 4.0 in
Appendix K). The analyses involved evaluating the final development phase of the LRP (see Table 9.0 for
the complete list of factors of safety). The minimum factor of safety, using the sensitivity-sh~le analyses
parameters, for the reconfigured LRP is 1.63 on Profile'_ and 3.
The stability of the LRP, durin¢ an earthquake event, was also investigated using an assumed maximum
horizontal and vertical around acceleration of 0.1 g (earthquake loading factors). The minimum
psuedostatic factor of safety analysis was found to be 1 '6 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 8 -Summary of Stability Analysis Results Factors of Safety (F.S.)
~;
Profile: Percentage Fines' Static: Factor of Safety Psuedostatic: Earthquake (F.S.)

Profile 1:7.6 % 2.='_ 1.89
10 % 1.67 1.30
20 % 2.38 1.72
30 % 254 1.90

Profile 2: 7.6 % 2.23 1.76
10 % 1.63 1.27
20 % 1.96 1.~4
30 % 2.24 1.77

Profile 3: 7.6 % 2.6~ 2.14
10 % 1.63 1.26
20 % 2.23 1.77
30 % 2.68 2.17

1. Percentage fines represents the amount of coal, as a percentage of [he total amount of coal, that has
passed the x200 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 perimeter to properly connect the existing refuse
fill with Phase V fill. The keytivays were located: I) along the base of the existing north and east faces of
the LRP, and 2) along the existine bench which extends around the north and east faces at the 6'_30-feet
contour. Keyways were cut with 2H:1 V sideslopes to a minimum relative depth of '_-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-fee[.
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