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• SENECA COAL COMPANY <br />SEDIMENTATION POND 015 STABILITY ANALYSIS <br />1.0 INTRODUCTION <br />1.1 PURPOSE <br />The purpose of this calculation brieFis to estimate the static factor of safety (FOS) for Sedimentation <br />Pond 015 using available soil data obtained from soil testing and the pond 015 configuration. <br />1.2 METHODOLOGY <br />The static FOS for the sedvnentation pond was estimated using a basic, two-dimensional equilibrium <br />analysis program called SLOPE/VC'. The FOS determined is the ratio of resulting resisting forces to <br />driving forces. Resisting forces are the internal strength parameters of the soil materials used in the <br />construction of the embankment and the underlying base materials upon which the facility will be <br />constructed. Driving forces aze produced by the weight of the embankment and bedding materials <br />as well as the water volume impounded in the pond. For this analysis, a circular failure mode was <br />assumed. The FOS was calculated using the Bishop method. <br />1.3 PROCEDURE: <br />The analysis was conducted using the as-built design configuration and cross section for Sediment <br />Pond 015 as shown on Exhibit 13-9 (I.eidich, 2000). For the analysis, it was assumed that the water <br />surface behind the embankment was at an elevation equal to 7,390 feet above mean sea level (ms!). <br />11tis water surface elevation is based on the invert of the principal spillway. <br />The embankmen[ was designed to be constructed with upstream and downstream slopes not steeper <br />than 3H:1V. The crest of the embankment was constructed with a width approximately equal to 15 <br />feet. The upstream height (measured from top of embankment to upstream toe) is approximately 14 <br />feet, with an additional 3 vertical Eeet of incised excavation. The downstream height (measured from <br />top of embankment to downstream toe) is approximately 20 feet. The base of the embankment <br />gradually slopes from the upstream embankment toe to the downstream embankment toe. <br />A phreatic surface was generated based on the permanent water surface elevation of 7,390 ft-msl <br />equivalent to the invert of the principal spillway. The phreatic surface through the embankment was <br />estimated based on Dazcy's law and observation of similar homogenous pond embankments at the <br />mine site. At these locations seepage does not occur above the embankment toe. The resulting <br />surface is shown on the SLOPE/W computer printouts contained in Appendix B. <br />Prior to construction, 2 soil samples were collected from the foundation azea (851-01 and 02) and <br />two samples were collected Etom the borrow areas (85l 03 and 04). Grain size and Atterbecg limits <br />were nn on all of the samples and the results aze shown on Table 1. <br />Soil shear strength properties Eor the pond foundation and embankment were determined by <br />comparing the results of index classification tests (particle size data and Atterburg limits) for soils in <br />the area. The index test results and shear strength Eor the soils tested for ponds at the stte are shown <br />. in Table 1. The Pond 14 results were selected to represent the strength properties of the Pond 15 <br />foundation soils due to the similarity in index properties. The sample of the Pond 14 foundation soil <br />was collected by excavating a test ptt and sampling with a Shelby mbe. An effective stress friction <br />