PERMFILE58368

• Permit No: C1981020A
• IBM Index Class Name: Permit File
• Doc Date: 11/4/2002
• Section_Exhibit Name: 2.0 Mine Plan
• Media Type: D
• Archive: Yes

2. •~_~
As shown in Figure 2.2-12.13, it was decided to eliminate the
• catching toe bench, use 0.5H to 1V in the uncovered rock, then a
safety bench 10 feet wide. This shifted the toe of the colluvial
cut out about 10 feet, providing mass at the toe. This extra mass
combined with a cut slope of 1.5H to 1V yielded a factor of safety
of 1.199 for the road cut.
Reclamation design was also altered by altering the design cut. The
goal, once again, was to increase the safety factor over the design
road. Material at the top of the slope will be pushed down the cut
to the toe where a compacted buttress will be constructed. The
factor of safety was computed for both soil and rock boundaries and
yielded factors of safety of 1.596 and 1.484 respecti•~ely.
A tabulation of data and results can be seen in Table 2.2-3. Cross
sections of each case analyzed are shown in Figures 2.2-12.11
through 2.2-12.14. Revised plan and reclamation maps are also
submitted for insertion into the permit application.
Analysis of the cut at Station 97+00 was at first considered to be
the most critical but analysis of design shows an increase in factor
of safety above both original ground and existing cut. Original
ground exhibits a safety factor of 1.045. The existing road cut has
a safety factor of 1.040. The design road cut has safety factors of
1.107 and 1.106; respectively, when rock or soil boundaries are
analyzed.
• As with reclamation on Line 1, reclamation on line 2 consists of
excavating material from the crest of the cut to construct a
buttress at the toe of the cut. Safety factors are 1.235 for rock
boundary and 1.259 for a soil boundary. Additional cross sections
are in Figure 2.2-12.21 through 2.2-12.24 and data is shown in Table
2.2-4.
The original ground at Line 3 (Station 90+00) had a relatively high
factor of safety, 1.271, as compared with the other cases analyzed.
Instead of relatively weak colluvial soils as in Lines 1 and 2, Line
3 has largely alluvial soils with much better r_haracteristics. The
existing road cut reduced the factor of safety to approximately
1.116. Once again, it must be stated that all factors of safety are
only relative indications of slope stability. Historically, the cut
slope at line 3 has been more stable than those at lines 1 and 2.
Calculated factors of safety have shown this trend. Since all cuts
have been stable, it can be seen that assumptions used for design
are conservative. If a lower factor of safety than 1.0 had been
calculated for any cut, data used in calculations would have to be
adjusted since all cuts are now stable.

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