2011-09-30_PERMIT FILE - C1980007A ‎(2)‎

• Permit No: C1980007A
• IBM Index Class Name: Permit File
• Doc Date: 9/30/2011
• Doc Name: Refuse Pile Expansion East
• Section_Exhibit Name: Exhibit 82 Refuse Pile Expansion East
• Media Type: D
• Archive: Yes

(static) and 2 -4 (seismic) provide modeling results for the colluvium residual shear strength ESSA.
Figures 2 -5 (static) and 2 -6 (seismic) show the results for the 2D USSA.
The 3D modeling results for static conditions are shown in Figures 2 -7, 2 -8, and 2 -9 for the
colluvium fully- softened shear strength ESSA, the colluvium residual shear strength ESSA, and the
USSA.
It can be seen in Table 2 that the computed 3D factors of safety are approximately 0.4 higher than the
2D factors of safety. This is likely the result of the effect of the shear resistance along the flanks of
the potential failure surface, and the slope geometry is more accurately represented in this manner.
The 3D modeling results indicate that the static ESSA factors of safety are greater than 1.5 for both
colluvium shear strength cases, and the static USSA factor of safety is greater than 1.2. While the
seismic factors of safety were not computed using the 3D models, they are considered adequate based
on the results of the 2D models and the 3D effects computed with the static models.
2.2.3.2 Geotechnical Design
A sampling, testing and monitoring plan, as presented in Appendix C, will be implemented as part of
RPE East operations to verify the refuse characteristics during actual refuse placement and to
monitor refuse pile conditions.
An initial evaluation will be conducted over the first two years of CPP operations when the refuse
pile is very small and there is no danger of instability and will be performed as described in the
sampling, testing and monitoring plan. Test results will be compared to the results already collected
from the field and the laboratory as discussed in Sections 2.2.2.1 and 2.2.2.2 and used in the
geotechnical design presented in this section.
2.3 Subsidence
The potential for subsidence related to mining activity in the area of the RPE East was examined.
Historically, the Oliver Mine developed the E -Seam near the current elevation of Highway 133
(Elevations 6,130 to 6,300 in the area underneath the proposed RPE East refuse pile). This mine
used the room - and - pillar mining technique in which pillars of coal remain after mining is completed
to support the roof. This type of mining typically results in very little subsidence observed at the
Revised July 21, 2011 Y o
P \Mpls \06 C0126 \06261003 RPE E. Permit Mod Support\WorkFiles \Permit Application \Text \Exhibit 82 RPEE design 2011 -07 -21 TR 127 doc 10