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Slope Stability Analysis <br />Varra Gravel Operation - Heintzelman Pit <br />Longmont, Colorado <br />Page 2 <br />The author used the software package PC-STABL to evaluate slope stability. Simulations <br />using Spencer, Modified Bishop and Modified Janbu methods were run to determine the <br />most conservative safety factor. The soil characteristics as presented earlier were used in <br />the analysis. Computer generated data sheets are presented in Attachment A. <br />A review of Attachment A shows proposed bank profiles are stable with a calculated safety <br />factor 1.34 during mine side dewatered conditions. Simulations for pit side flood conditions <br />(static water surface) indicate a safety factor of 1.86. <br />Discussion <br />Slope failure analyses for proposed open cut gravel operations at the Varra <br />Heintzelman site indicate proposed slope cuts will be stable for dewatered or static <br />water table conditions. The soil slope angel from the horizontal is much less than the <br />internal friction angel associated with sand and gravel deposits. The high permeability <br />of the bank material reduces the potential for excessive pore pressures within the bank <br />during rapid drawdown events such as dewatering. If any significant modifications to <br />proposed slopes occur this analysis should be considered invalid. <br />Comments <br />The discussions and recommendations in this report represent our professional opinions. <br />Our conclusions, opinions and recommendations are based from information available at <br />this time and we do not guarantee that undiscovered conditions will not become evident in <br />the future. CGRS' report was prepared in accordance with currently accepted engineering <br />practices at this time and location and no other warranties, representations or certifications <br />are implied or intended.