REV11883

• Permit No: M1980244
• IBM Index Class Name: Revision
• Doc Date: 8/6/1998
• Doc Name: REVISED SLOPE STABILITY EVALUATION FOR PROPOSED INTERMEDIATE HAUL ROAD CONFIGURATION UPPER WQ
• From: GOLDER ASSOCIATES INC
• To: CRIPPLE CREEK & VICTOR GOLD MINING CO
• Type & Sequence: TR27
• Media Type: D
• Archive: No

24,1998 -2- 983-2348.195
In November, 1997, one test pit was excavated within the general area of the proposed
intermediate haul road using a Case 2080 trackhoe operated by Conley Construction of
Cripple Creek, Colorado. Results of this test pitting program compared quite well with the
results of the investigation program conducted in 1993 for the Ironclad Overburden Storage
Facility (Golder Associates, 1993. Report on Ironclad Rock Storage Area Stability,
Cresson Project, October). Soils were found to reach thicknesses in excess of 15 feet
along the valley floor and generally consisted of cobbles, gravel and sand in a silty clay
matrix overlain by a topsoil layer.
Based on visual observation of material encountered in the test pit, Golder has used the
same material properties in this analyses as those presented in the earlier analysis
performed by Golder (Golder, 1993.). The following material properties were used for the
slope stability evaluation:
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Mine Overburden 120 130 39 0
Foundation Soils 110 120 29 0
Bedrock 120 120 40 1000
The primary potential failure mode considered in this stability analysis consisted of a block
or wedge failure through the foundation soils below the overburden material. While
circular surfaces are also possible, this potential failure mode typically consists of shallow
surface raveling, whereas the wedge failures would involve large intact blocks of the
overburden material translating horizontally. Therefore, the wedge failure mode was
considered more critical for this application because it would involve significant volumes of
displaced material, while the surficial slope raveling represents only relatively small slope
adjustments affecting small amounts of overburden material.
The static factor of safety (FOS) associated with deep seated movements along Section A-
A' was computed to be 1.2. Apseudo-static FOS of 1.0 was calculated for a peak ground
acceleration of 0.088. The section was developed based on the following configuration:
overburden material (placed at a 1.8H:1V sideslope) would be placed on a 10 foot thick
layer of foundation soils which overlay a competent foundation material. As the base
topography represents the top of a ridge where groundwater is not usually encountered, no
phreatic surface was used in the analysis. The static FOS for deep seated movements along
Section B-B' was computed to be 1.4. Apseudo-static FOS of 1.2 was calculated for a
peak ground acceleration of O.O8g. This section was taken along the low point of the
drainage, and was based on the following configuration: overburden material (placed at a
1.SH:1V sideslope) would be placed on 10 feet of foundation soils which overlay a
competent foundation material. As this was the low point of the drainage where
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