PERMFILE41795

• Permit No: M1980244
• IBM Index Class Name: Permit File
• Doc Date: 8/1/2005
• Doc Name: geotechnical analyses
• From: cripple creek and victor gold mining company
• To: dmg
• Media Type: D
• Archive: No

Cripple Creek & Victor Gold Mining Company July 21, 2005
Timm C. Comer -3- 053-2399
The prism survey data was also analyzed using the method presented by Pettey et al. (2002). This
method of analysis is commonly used to evaluate potential landslide and slope stability problems and
consists of plotting the time-series of the inverse of velocity for each prism. The shape and slope of
the time-series of the inverse of velocity are then used [o assess the type of behavior within the slope.
In general, if a slope is trending toward potential failure, the velocity of movement will increase with
time as crack growth and ducleation occurs. As the velocity increases, the inverse of velocity
decreases. The intercept of the inverse of velocity line with the time axis can then be used to estimate
the potential time to failure. Studies on failing slopes have indicated that the shape of the inverse
velocity curve can be related to internal mechanics:
Linear trends occur when crack growth is the dominant process within the mass;
and
• Non-linear [rends develop as slidiag occurs along apre-existing shear surface
A typical inverse velocity plot is shown in Figure 3. Appendix B presents time-series plots of prism
data for the SGOSA, and include: total displacement, velocity, and inverse velocity. As evident from
the time-series plots, there is considerable variation in the velocity and inverse velocity curves of the
SGOSA prisms. The measurement records show velocity increases and decreases over time without a
definite trend. This type of behavior indicates that the prisms are not monitoring a potential failing
slope, where movements would be more consistent. The prisms are monitoring a mass that is moving
at different rates, which would be more indicative of three-dimensional deformation related to
settlement. Therefore, based on the prism data, the measured movements of the SGOSA facIlity are
not indicative of potential major slope failure.
Slope Stability Analysis
A slope stability analysis was conducted to further verify the interpretations and conclusions reached
based on the prism data. The slope stability analysis was conducted on a critical cross-section section
cut through the facility. The location of the critical cross-section and the cross-section itself is
presented in Figure 4. The critical cross-section is along the axis of Squaw Gulch, where there is the
maximum overburden thickness with a minimal buttressing effect from the valley sideslopes.
The stability analyses included overburden, subgrade soils, and bedrock. The material properties used
for the ana]yses are summarized in Table 1. The shear strength of the overburden was back-calculated
using the observed angle of repose and fitting the data to rockfill shear strengths presented by Leps
(1970). The results of the stability analyses are presented in Appendix C.
The stability analyses were conducted using SLIDE 5.0, a commercially available computer program
(Rocscience, 2000). Stability analyses were conducted for both static and earthquake loading
scenarios. For each loading scenario, arcuate modes of failure were analyzed using Spencer's method
(Spencer, 1967) to determine the least stable failure surface via the critical surface search routine.
Static loads were calculated based on self-weight of the overburden and subgrade materials.
The stability analyses focused on-theoretical, relatively deep-seated failure surfaces involving a
significant volume of overburden and the subgrade materials at the base of the facility. Shallow slip
surfaces involving only the "outer skin" of the overburden materials in the SGOSA facility aze not
germane to a stability analysis. Such shallow-seated movements aze expected as part of waste
i~.osz~vmacroscosasr~n~.~mziasosrzss.aooam.da Golder Associates