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]u~~ 1999 Suiera Coa! Comfmrry~ * Senem II lf% D(rrre Sedrmeatnlion Po+rd 01 G Stnbrtip~ slnaly+ir ~ 1 <br />• 1.0 INTRODUCTION <br />1 <br />1.1 PURPOSE <br />The purpose of [his stability analysis is to calculate [he safety factor (SF) under static conditions for the <br />Sedimentation Pond 016 embankment in order to document design compliance with applicable regulatory <br />standards under Rule 4.05.6(11)(j) or (k). <br />1.2 METHODOLOGY <br />The static SF for Sedimentation Pond 016 was calculated using a basic, one-dimensional equilibrium <br />analysis program called XSTABL (v6.2). The calculated SF is the ratio of [hose resisting forces that would <br />prevent embankment movement or failure [o the corresponding driving forces. Resisting forces include the <br />internal sveng[h parameters for both [he soil materials used in [he construction of [he embankment and [he <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 [he embankment. For this analysis, a <br />circular failure mode was assumed, and [he SF was calculated using [he Bishop method. <br />1.3 PROCEDURE <br />The embankment cross-section shown on Exhibit 13-8A of the Seneca II W Permit, (Leidich, 1999), was <br />used to evaluate embankment stability. For the analysis, a water surface elevation behind [he embankment <br />of 7,462.5 fee[ above mean sea level (ams]) was used. This water surface elevation is equivalent [o the <br />elevation of the invert to the principal spillway. <br />The embankment is designed with upstream and downstream slopes of 3H:1V. The design width of the <br />•~ embankment crest is 15 fee[. Total height from [he bottom~of [he pond to [he top of the embankment is 21 <br />feet. The emergency spillway invert is 2.5 fee[ below the embankment crest. As designed, [he base of the <br />embankment slopes from the upstream embankment toe to the downstream embankment toe at <br />approximately 6%. <br />The potential phreatic surface for the stability analysis is based on a water surface elevation of 7,462.5 ft- <br />amsl cotresponding to the invert elevation of the principal spillway. The phreatic surface through the <br />embankment was estimated based on Dazcy'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 [he soils in the area aze defined as a Binco silty clay loam and a Cou[is fine sandy <br />loam. A complete soil description of this soil type can be found in Appendix A. Properties for this soil <br />type are shown on Table I Sedimentation Pond 016 Soil Data. <br />TABLE 1 <br />SEDIMENTATION POND 016 SOIL DATA <br />SOIL No. SOIL NAME ATTERBERG PARTICLE SIZE US CS <br /> LIMITS DATA CLASSIFICATION <br /> (LL - PI) (% assin No. 200) <br />] 1 D Binco silty cla loam 35 to 60- 15 to 35 72- 92% CL-CH <br />34D Coutis fine sand loam 20 to 30 - 5 to l0 30 - 50% SM-SC <br />. The soil strength properties for the natural soils were obtained from published data for common soils (Luo <br />' and Peng, 1999). The soil information can be found in Appendix A. According to the published data for a <br />Afomtgomery U%ntton Amenm; Ira 165 So+dh Union Boulevard, Strih 410 * Lnkewoad, ColoraAo 80228 * (303) 7G3-5140 <br />J: \Yi 1 \npnl\DnrsdlGrtoGi(r0~ <br />10/IN/99 r,h <br />