Laserfiche WebLink
Continued. <br />Crushed Ore and Drain Cover Fill. The crushed ore and drain cover fill were modeled <br />using an angle of internal friction of 40 degrees with zero cohesion, based on previous <br />testing performed on Cresson ore material. <br />Composite Liner. Interface shear strength testing has been conducted at multiple times <br />during design phases of the Cresson and SGVLFs (AMEC, 2011) to evaluate the shear <br />strength along various interfaces of the composite liner system. For these analyses, the <br />interface shear strength criteria used in the AMEC (2011) design report were adopted, <br />consisting of residual (at 45 mm displacement) interface friction angle of 23.5 degrees <br />and zero adhesion. It must be noted that most of the interface shear testing conducted <br />to date presents values for textured geomembrane (LLDPE and HDPE) failing along the <br />soil liner fill interface as this interface tends to be more critical than the interface of <br />granular fill along smooth geomembrane (as is the case in the PSSA). To address this <br />uncertainty, a sensitivity analysis was conducted for the interface shear strength between <br />drain cover fill and smooth LLDPE geomembrane. <br />Foundation Material. The foundation material shear strength was modeled with an <br />angle of internal friction of 40 degrees and zero cohesion, which represents either a <br />bedrock foundation or a granular fill foundation. <br />Phreatic Surface. The phreatic surface internal to the PSSA was modeled for various <br />conditions, including: (i) completely dry conditions (including no pond); (ii) completely <br />saturated drain cover fill; and (iii) pond in PSSA at current elevation 9,377.9 feet. <br />3.4 Results of Stability Evaluation <br />Stability analysis results for each of the critical stability sections are summarized in Table <br />2. Although both block and circular failure surfaces were evaluated, block type failures <br />along the liner system resulted in critical factors of safety. The output from the stability <br />analyses is presented in Appendix B. <br />Table 2 - Results of Stability Evaluation <br />Cross -Section / Condition <br />Factor of Safety <br />Static <br />Pseudostatic <br />(k=0.14) <br />Section A - No pool, dry conditions <br />1.2 <br />- <br />Section A - Pool elevation 9,377.9, saturated DCF <br />1.1 (localized) <br />1.3 (large scale) <br />0.9 <br />Section A - Ore placed to elevation 9,378 in PSSA <br />1.2 <br />1.2 <br />Section B - No pool, dry conditions <br />1.1 <br />- <br />Section B - Pool elevation 9,377.9, saturated DCF <br />1.0 <br />0.8 <br />Section B - Ore placed to elevation 9,378 in PSSA <br />1.5 <br />1.1 <br />As presented in Table 2, the stability evaluations conducted indicate that the factors of <br />safety for existing conditions at the PSSA do not meet the minimum criteria outlined in <br />Page 4 of 7 <br />