2008-04-15_REVISION - M1980244 ‎(192)‎

• Permit No: M1980244
• IBM Index Class Name: REVISION
• Doc Date: 4/15/2008
• Doc Name: VOL IV APP 5 Attachment 2 Globe Hill Mine Slope Design
• From: CC & V
• To: DRMS
• Type & Sequence: AM9
• Media Type: D
• Archive: No

GHMXSIopeEvaluation
GLOBE HILL MINE EXPANSION SLOPE DESIGN SUMMARY
1. The slopes of the proposed Globe Hill Mine Expansion (GHMX) have been evaluated and
designed.
2. A total of 26 geotechnical holes were logged and samples strength-tested to obtain information
for the design of the GHMX slopes.
3. The materials in the GHMX walls will be predominantly highly fractured and weathered
volcanic breccia and phonolite. The Globe Hill pipe is located on the east side of the GHMX,
and is made up of very weak, highly fractured and weathered volcanic materials, with significant
intersections of intact anhydrite and fluorite.
4. The mine wall will contain only small quantities of surficial alluvium comprising dense, clean
volcanic and granitic particles, with limited clay.
5. The mine has been previously mined and backfilled. The backfill will be removed during the
expansion, and no backfill will remain in the final mine slopes.
6. The wall rocks are of generally low intact strengths, with the following unconfined compressive
strengths:
•
a. Volcanic material near the pipe: approximately 500 psi.
b. Anhydrite in the pipe: approximately 2,000 psi
c. Volcanic material west of the pipe: approximately 8,000 psi.
7. The structure of the GHMX area is dominated by the Globe Hill pipe. Structural features (the
pipe, and major faults) are sub-vertical. However, the entire area is highly fractured and
weathered, resulting in low RQD, low intact strength, and low overall rock-mass quality.
8. Discontinuities in the rockmass are in general strong, with an overall friction angle in excess of
40°, and significant cohesion in rubble samples.
9. Slope stability at GHMX is principally governed by the rock quality. For the height of wall
proposed at GHMX (maximum 600 foot), the following slope angles have been determined.
Predominant Slope Material Alluvium/
Colluvium Very Poor
Rock Poor
Rock Fair
Rock
Overall angle degrees 36° 40° 50° 55°
Berm width feet 17.5 45 35 35
Inter bench angle degrees 40° 79° 79° 79°
Intermediate berms feet 1 30 16 9
Bench height feet 3@35 3@35 3@35 3@35
10. Slope excavation at the GHMX will require special attention to blasting practices:
•
a. Pre-split or trim blasting using close-spaced blast holes on each bench.
b. Depth control on blast holes on the level above benches.
c. Location control to avoid blasting on the future crest.
Report 1385E.20071126