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Juh 7979 Scum Coal Comparg * }'oar! dlirre Sedlmur7ation Pard 013 SlabrGg Anu)rir I 1 <br />• 1.0 INTRODUCTION <br />1.1 PURPOSE <br />The purpose of this stability analysis is to calculate the static safety factor (SF) for the Sedimentation Pond <br />013 embankment in order to document design compliance with applicable regulatory standards under Rule <br />4.O~b(l l)(j) or (k). <br />1.2 METHODOLOGY <br />The static SF for Sedimentation Pond 013 was calculated using a basic, one-dimensional equilibrium <br />analysis program called XSTABL (v5.2). The calculated SF is the ratio of those resisting forces [ha[ would <br />prevent embankment movement or failure to the corresponding driving forces. Resisting forces include [he <br />internal strength parameters for both the soil materials used in the construction of the embankment and the <br />underlying base materials on which the facility will be constructed. Potential driving forces include <br />gravitational forces on the embankment and foundation materials and the gravitational and lateral forces <br />associated with the water volume that could be impounded behind the embankment. For this analysis, a <br />circular failure mode was assumed, and the SF was calculated using the Bishop method. <br />1.3 PROCEDURE <br />The embankment cross-section shown on Exhibit 13-1?.2 of the Yoast Permit, (Leidich, 1999), was used to <br />evaluate embankment stability. For the analysis, a water surface elevation behind the embankment of <br />7,366 feet above mean sea level (msl) was used. This water surface elevation is equivalent to the elevation <br />of the invert to the principal spillway. <br />• The embankment is designed with upstream and downstream slopes not steeper than 3H:1 V. The design <br />width of the embankment crest is IS feet. The upstream height (measured from the top of the embankment <br />to the original upstream channel elevation) is approximately 12 feet. Total height from the bottom of the <br />pond to the [op of the embankrrtent is I ~ feet. As designed, the base of the embankment slopes from the <br />upstream embankment toe to the downstream embankment toe at approximately 8`70. <br />The potential phreatic surface for the stability analysis is based on a water surface elevation of 7,366 ft-msl <br />corresponding to the invert elevation of the principal spillway. The phreatic surface through the <br />embankment was estimated based on Darcy's Law and Casagrande's procedure as outlined by Huang <br />(1983). The resulting surface is shown on the XSTABL computer printouts contained in Appendix B. <br />Based on soil surveys performed by Jim Nyenhuis (1993 - 1996) and as indicated in Table I, the soil and <br />subsoil materials in [he Sedimentation Pond 013 area are predominantly slightly sandy to sandy clays. <br />These materials are of a similar type to the soils previously collected and analyzed for Sedimentation Pond <br />O10 based on soils mapping information and NRCS soils characterizations. Given reasonable <br />comparability based on soil type, the soil physical parameters previously determined for Sedimentation <br />Pond O10 have been used in the stability analysis for Sedimentation Pond 013. <br /> <br />blar(gomrp~ lF/almn fLnrrrrru, Inr. 1G5 Saulh Union Bou/ward, Suilr 110 * Lnkrmood, Co/orada 80??8 * (303J IG3~5140 <br />J: \8i 7 \nporr~Dandl IrrabiGry <br />07/ IG/77 r.b <br />