REV100176

• Permit No: M1977211
• IBM Index Class Name: Revision
• Doc Date: 12/12/2000
• Doc Name: MEMO-PIKEVIEW QUARRY SLOPE STABILITY M-77-210
• From: DMG
• To: LARRY OCHLER
• Type & Sequence: AM2
• Media Type: D
• Archive: No

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STATE OF COLORADO
DIVISION OF MINERALS AND GEOLOGY
Deparimen[ of Natural Resources
1313 Sherman 51., Room ? 15
Denver, Colorado 80?03
Phone: [phone]
FAx: (303) 83~-8106
December 12, 2000
To: Larry Oehler
From: James Dillie ~~
Re: Pikeview Quatry Slope Stability, M-77-211
DIVISION OF
MINERALS
GEOLOGY
RECLAMATION
MINING•SAFE TY
Bill Owens
Governor
Greg E Watcher
Ezecwive Director
Michael B. Long
Division Director
Per your request, I completed a cursory review of Exhibit T involving Dr. John Abel's slope
stability report.
The proposed amendment application provides information regarding the mining activities in the
north end of the quarry and the proposed method of reclaiming the area. Briefly, the operator
proposes to mine (layback) the mountainside in a configuration (bench and highwall) that will be
stable and look more like the natural undisturbed terrain after vegetation re-establishes.
The operator proposes to leave a sloped highwall (with several I.5:1 benches) which will be
partially revegetated and is designed to be stable. Stability will be achieved by creating an overall
slope gradient of 49 degrees which is less than the 60 degree dip of the granite joint sets.
Projected factors of safety (FOS) range from 7.4 to 41. It is not clear whether these are static or
pseudo-static calculations. However, if they are static factors of safety they appear large enough
that including a seismic coefficient in the calculation would, most likely, not reduce the FOS
below the point of equilibrium (when the driving forces equal the resisting forces).
Occasionally, geologic conditions change as quarry mining activities progress. A significant
change could drastically alter projected stability conditions which could require modifying the
mining plan. The operator suggests inspecting the mined cliff and slope configuration to verify
"[he stability and parameters" [o ensure the mined slope is stable prior to topsoiling and
revegetating the benched areas. It could be problematic if the slope is determined unstable after
the topsoil is replaced and the area reseeded since the operator will, most likely, be required to
reconfigure the slope if it is not stable. A technical revision, or permit amendment, submittal will
be required to modify the highwall design if, sometime in the future, it is determined not to be
stable. Periodic inspections are highly recommended. Also, if the operator observes changing
geologic conditions during mining operations, the Division should be notified.
If, at depth, geologic conditions do not drastically change, the proposed highwall configuration
has a high probability of remaining stable after the site is reclaimed (a degree or two change in
the dipping joint sets will not be considered drastic enough to be concerned with).
cc: James Stevens