2013-02-15_PERMIT FILE - C1981020 ‎(2)‎

• Permit No: C1981020
• IBM Index Class Name: Permit File
• Doc Date: 2/15/2013
• Section_Exhibit Name: 3.0 Reclamation Plan
• Media Type: D
• Archive: No

STATION 18+00
The analysis of this area was complicated by the fact that the original slope was
not extremely stable, a common condition in the mine area. The analysis of the
assumed original slope indicates a factor of safety of only 1.154. The existing
configuration with the road had a factor of safety of 1.081. Since the slope had shown
no tendency of failing in the nearly thirty years, it is assumed that the soil parameters or
underground stratigraphy is not accurately defined within the data set. Although a "true"
factor of safety was not generated, the relative stability of the various configurations
was attained.
The next configuration that was tested for this line was for.the reclaimed
configuration. The analysis yielded a factor of safety of 1.166. The reclaimed
configuration includes backfilling the cut with material that will be compacted to achieve
a density of 135 pounds per cubic foot, while it was assumed that the original ground
has a density of 120 pounds per cubic foot. The backfill was also assumed to have a
higher cohesion, 300 vs. 200 psf, since it will be a blend of the existing gravelly material
and the hi hl cohesive soils found in the u er opion t
9 Y pp p s of the road. It was noted tha
none of the failure circles generated by REAME intersected the reclamation backfill.
Therefore, the failure would occur in the host material not in the backfill.
Since this analysis did not yield a factor of safety of 1.3 or higher, and none of
failure circles involved the backfill, analysis of just the backfill was performed. The
analysis of the backfill itself indicated a factor of safety of 2.115. Since the backfill was
shown to be stable, the stability of the original configuration is the weak point. No effort
to enhance the overall stability of the slope would be capable of creating a 1.3 factor of
safety without a major reduction in the steepness of the original slope. This option is not
feasible.
There was not adequate material available to backfill the cut slope as shown on
Figure 3.1-8. Thus, a significant remnant cut slope was left in place. The backfill
should be more stable than explained above because it was constructed to a flatter
slope than anticipated. The remnant cut slope has been stable for nearly thirty years so
it should remain relatively stable for the foreseeable future.
TR-23 3-10 12/07