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To: Chris Nyikos <br />From: Philip B. Solseng <br />Subject: Stability Analysis Results <br />Date: 16 September 2009 <br />Project: Pond MB5E Evaluation <br />c: Jed Greenwood, Brad Lindsay <br />1.00 against upstream slope failure for the normal pool elevation and a 100-year river flood event. The <br />minimum factor of safety for the undrained (USSA) case was 3.38 for the normal pool cases. The <br />minimum factor of safety for the drained (ESSA) case was 1.00 for the extreme seepage case (river flood <br />with steady-state seepage) and a normal pool in the pond. As seen in the model outputs in the Appendix, <br />the potential failure surface is fairly small relative to the interior (upstream) slope height of the <br />embankment and any potential deformation would likely result in maintenance and not a dike breach. The <br />resultant factors of safety for all static analyses are included in Table 3, and all stability model outputs are <br />attached in the Appendix. <br />Table 3. Analysis Results - Static <br /> Factor of Safe <br />Case Direction USSA ESSA <br />Maximum Pool El. Downstream 7.72 1.36 <br />Normal Pool El. Upstream 3.38 1.43 <br />Normal Pool El. with <br />Flood <br />Upstream <br />3.38 <br />1.00 <br />The results of the pseudo-static analysis using a PGA of 0.166g indicate a factor of safety of 2.03. This <br />corresponds to the normal pool elevation for the USSA on the upstream slope. The resultant model <br />output for the pseudo-static analysis is attached in the Appendix. <br />SUMMARY <br />The results of slope stability analysis indicate that the factors of safety are adequate given the seepage and <br />loading conditions described above. According to Rule 4.05.9(8)(b), a static factor of safety of at least <br />1.3 must be achieved for a normal pool with steady-state seepage, and the resulting factor of safety for <br />2H:1 V slopes and a 12-foot crest width is 1.43. Thus, the embankment will be stable when constructed <br />using the following specifications: <br />• Slopes equal to or flatter than 2H:1 V <br />• Crest width equal to or wider than 12 feet <br />0 Constructed of colluvial material which comprises predominantly fine-grained (cohesive) soils