REV07535

• Permit No: M1980244
• IBM Index Class Name: Revision
• Doc Date: 8/6/1998
• Doc Name: PAD 1 SLOPE STABILITY EVALUATION
• From: GOLDER ASSOCIATES INC
• To: CRIPPLE CREEK & VICTOR GOLD MINING CO
• Type & Sequence: TR27
• Media Type: D
• Archive: No

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forces while pseudo-static analyses modeled design seismic conditions by incorporating a
constant horizontal force. For the pseudo-static analyses, 0.14g was used as the seismic
coefficient in the slope stability models. The criteria used to determine the acceptability of
the sideslope revision were: (1) the static FOS must be greater than 1.3 and (2) the pseudo-
static FOS must exceed 1.0.
MODEL DEVELOPMENT
The geometric profile of the stability model developed consisted of crushed ore, a composite
liner, and the foundation material. The FOS was calculated for overall slopes of 1.6H:1V, to
a maximum depth of 320 feet, as shown in Figure 1. The ore is underlain by a composite
liner consisting of a 1-foot-thick Soil Liner overlain by a geomembrane. Foundation
material, assumed to be bedrock, or clean and granular native soils, was modeled beneath the
composite liner.
The piezometric head was modeled as 1 foot above and parallel to the lined surface, which is
consistent with the conditions used in Amendment Number 6.
The material properties used in the stability analyses aze discussed below, and summarized in
the following table:
Crushed Ore: For the stability analysis, the crushed ore material was modeled with an angle
of internal friction of 40 degrees with no cohesion, based upon site-specific testing performed
on Cresson ore material. The results of the site-specific testing performed on nominal 1-1/2
inch minus Cresson ore was reported to the OMLR in a January 9, 1996 letter from CC&V
titled "Cresson Project: Permit M-80-244: Procedures and Materials for 1996 Construction."
The in-place bulk density of the material is modeled at 110 pcf.
Composite Liner: Results from interface shear strength testing performed as part of the
Phase I Ore Storage Area showed that the Soil Liner Fill /geomembrane interface was the
weakest interface of the composite liner. Therefore, strength parameters of this interface was
incorporated into the stability model.
The composite liner used in the stability model is represented by one of the two following
configurations depending upon the location within the valley leach facility:
1. A 1-foot-thick layer of Ironclad Soil Liner Fill overlain by an 80-mil
smooth VLDPE geomembrane liner, representing the material used as
the composite liner for Phase I. Interface direct shear testing results
were presented to the OMLR in Amendment Number 6 as part of
Golder's October, 1993 report titled "Permitting Level Design
Evaluation of the Expansion of the Mining and Ore Processing Facilities:
Cresson Project". While a residual angle of internal friction of 28
degrees and a cohesion of 1,635 psf were measured, the composite liner
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