2009-03-02_PERMIT FILE - C1980004 ‎(5)‎

• Permit No: C1980004
• IBM Index Class Name: Permit File
• Doc Date: 3/2/2009
• Section_Exhibit Name: Appendix R Stability Evaluation of Proposed Gob Wastepile
• Media Type: D
• Archive: No

Table 3. Effective Stress Shear Strength Parameters of Gob
From CU Triaxial Testing
Remolded Remolded
Sample Dry Density Moisture ~' Cohesion,
Ip (pcf) Content (%) (degrees) c' (psf)
1 71.6 to 73.2 20.6 to 22.0 3:2 0
5.0 STABILITY EVALUATIONS
Slope stability of the proposed the gob pile was evaluated using two-dimensional limiting
equilibrium stability analyses with the computer software SLIDEdev~eloped by Rocscience
(2004). The factor of safety was determined for critical circular arid block-type failure surfaces
using total and effective stress analyses. The simplified Bishop and Spencer procedures were
used and only static loading conditions were evaluated.
5.1 Cross-Sections and Geometry
Stability of the proposed gob pile was evaluated for two cross-sections, as indicated on
Drawing 3. Cross-section A-A' is a north-south trending section, while cross-section B-B' is
essentially an east-west trending section. The geometries of the sections are similar and
consist of 3H:iV (horizontal:vertical) side slopes and an ultimate maximum vertical height of 40
• feet.
The foundation soils were modeled as a single homogeneous mat~enial type. No bedrock was
incorporated into the model since bedrock was not definitely encounntered to depths of 51 feet
in the geotechnical investigation. Groundwater was not encountered within our boreholes.
Stability analyses were conducted both with and without groundwater to evaluate the sensitivity
to groundwater. A conservative estimate of 5 feet to the groundwater table was assumed to
evaluate shallow groundwater conditions.
5.2 Shear Strength Parameters
Total and effective stress strength parameters were estimated for compacted gob and
foundation soils based on our geotechnical drilling program, index testing, and triaxial
compression testing. Due to the anticipated variability of the gob nnaterial and uncertainty of
strength parameters, sensitivity analyses were conducted to evaluate the effects of variability of
gob strength parameters and unit weight. The strength parameters are discussed below for
gob and foundation soils. Table 4 presents the parameters used in the analyses.
5.2.1 Gob
Shear strength parameters for the gob were determined based on I1U and CU triaxial shear
tests as summarized in Tables 2 and 3. Total stress strength pararnoeters for the gob were
based on 3 UU triaxial shear tests, and effective stress strength parameters for the gob were
based on 1 CU triaxial shear test with pore pressure measurement. For the stability analyses,
the lowest undrained shear strength of the 3 UU triaxial tests was used. A conservative
estimate of effective strength parameters for the gob was used in the analyses based on one
McClave Canyon Mine stability report
Project #07-334-GEO
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