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January 9, 1996 -S- 943-2847. <br />001 <br />100 mil textured HDPE geomembrane /Area No. 2 Soil Liner Fill configuration, buc <br />allowed the Area No. 2 Soil Liner Fill material to consolidate completely prior to shearing <br />the sample. <br />When the consolidated interface shear strength test was performed, the material had a peak <br />cohesion of 1475 psf and a friction angle of 17 degrees, and a residual cohesion of 1315 <br />psf and a friction angle of 17 degrees. It was noted that the failure surface for both tests <br />occurred in the Soil Liner Fill, adjacent to the 100 mil textured HDPE geomembrane. <br />At the time the interface shear strength testing was being performed for the 100 mil <br />textured HDPE geomembrane, only double sided textured geomembrane was available. As <br />the weaker interface in the Low Volume Solution Collection Fill / 100 mil textured HDPE <br />geomembrane /Area No. 2 Soil liner Fill interface is the geomembrane /Soil Liner <br />interface, Golder considers the test result; o~tained for the double sided textured <br />geomembrane to be representative for one sided textured geomembrane. <br />Sloe Stability iyjodeling <br />Slope stability was evaluated according to the Force Method of Analysis (Force Method). <br />The Force Method considers potential failure masses as ri;id bodies divided into adjacent <br />regions or "slices", separated by vertical boundary planes and is based on the principal of <br />limit equilibrium, i.e., the method calculates the shear strengths which would be required <br />to just maintain equilibrium, and then calculates a "safety factor" by dividing the required <br />shear strength by the available shear percentage by which the available shear strength <br />exceeds, or falls short of, that required to maintain equilibrium. Therefore, safety factors <br />in excess of 1.0 indicate stability and those less than 1.0 indicate instability, while the <br />greater the mathematical difference between a safety factor and 1.0, the larger the "margin <br />of safety" (for safety factors in excess of 1.0), or the more extreme the likelihood of <br />failure (for safety factors less than 1.0). <br />The stability analyses were conducted using the XSTABL computer program. For the <br />wedge or translational failure modes, the operator manually iterated through a variety of <br />potential failure surface and calculated the factor of safety for each surface according to the <br />Janbu's Method Stability algorithm. The surace with the minimum factor of safety was <br />then selected as the critical wedge or translational surface. <br />In the design report prepared by Golder for CC&V in 1994 that was submitted to the <br />Office of Mined Land Reclamation (OMLR), critical slope stabiIiry sections were <br />developed for both the Phase I and Phase II Pads. In the original analysis, Golder assumed <br />an interface shear strength friction angle of 24 degrees and a cohesion of 100 psf, which <br />~3 was realistic for the Very Low Density Polyethelene /Ironclad Soil Liner Fill interface. At <br />~ the time the stability was performed, the pre-railings topography in the Phase II Pad was <br />not fully known. Golder has re-evaluated the .ritical Phase II Pad stability sections, using <br />the 1995 Phase II Pad post construction topography. Based on the topography, the <br />minimum strength requirements for the Soil liner Fili /geomembrane interface were back- <br />Golder Associates <br />