2019-06-19_REVISION - M1980244 ‎(2)‎

• Permit No: M1980244
• IBM Index Class Name: REVISION
• Doc Date: 6/19/2019
• Doc Name: Adequacy Review Response
• From: CC&V
• To: DRMS
• Type & Sequence: TR113
• Email Name: TC1
• Media Type: D
• Archive: No

January 9, 1996 -5- 943-2847.001
100 mil textured HDPE geomembrane / Area No. 2 Soil Liner Fill configuration, but
allowed the Area No. 2 Soil liner Fill material to consolidate com l.etelY prior to shearing
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the sample.
When the consolidated interface shear strength test was performed, the material had a peak
cohesion of 1475 psf and a friction angle of 17 degrees, and a residual, cohesion of 1315
psf and a friction angle of 17 degrees. It was noted that the failure surface for both tests
occurred in the Soil Liner Fill, adjaa.--nt to the 100 mil textured HDPE geomembrane.
At the time the interface shear strength testing was being performed for the 100 mil
textured HDPE geomembrane, only double sided textured geomembrane was available. As
the weaker interface in the Low Volume Solution Collection Fill / 100 mil textured HDPE
geomembrane / Area No. 2 Soil finer Fill interface is the geomembrane / Soil Liner
interface, Golder considers the test results obtained for the double sided textured
geomembrane to be representative for one sided textured geomembrane.
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Slope stability was evaluated according to the Force Method of Analysis (Force Method).
The Force Method considers potential failure masses as rigid bodies divided into adjacent
regions or "slices", separated by vertical boundary planes and is based on the principal of
limit equilibrium, i.e., the method calculates the shear strengths which would be required
to just maintain equilibrium, and then calculates a "safety factor" by dividing the required
shear strength by the available shear percentage by which the available shear strength
exceeds, or falls short of, that required to maintain equilibrium. Therefore, safety factors
in excess of 1.0 indicate stability and those less than 1.0 indicate instability, while the
greater the mathematical difference between a safety factor and 1.0, the larger the "margin
of safety" (for safety factors in excess of 1.0), or the more extreme the likelihood of
failure (for safety factors less than 1.0).
The stability analyses were conducted using the XSTABL computer program. For the
wedge or translational failure modes, the operator manually iterated through a variety of
potential failure surface and calculated the factor of safety for each surface according, to the
Janbu's Method Stability algorithm. The surface with the minimum factor of safety was
then selected as the critical wedge or translational surface.
In the design report prepared by Golder for CC&V in 1994 that was submitted to the
Office of Mined Land Reclamation (OMLR), critical slope stability sections were
developed for both the Phase I and Phase II Pads. In the original analysis, Golder assumed
an interface shear strength friction angle of 24• degrees and a cohesion of 100 psf, which
? was realistic for the Very Low Density Polyethelene I Ironclad Soil Liner Fill. interface. At
r the time the stability was performed, the pre-railings topography in the Phase II Pad was
not fully known. Golder has re-evaluated the :ritical Phase H Pad stability sections, using
the 1995 Phase II Pad post construction topography. Based on the topography, the
minimum strength requirements for the Soil liner Fill / geomembrane interface were back-
Golder Associates