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Alnn'h ?000 Soren Coa/ Carrr~any • }'oat! et9tnt SrrGmturoliai Pond O75 SmMGg~ Aun/ysir 1 Pagr ! <br />• SENECA COAL COMPANY <br />SEDIMENTATION POND 012 STABILITY ANALYSIS <br />1.0 INTRODUCTION <br />1.1 PURPOSE <br />The purpose of this calculation brief is to estimate the static factor of safety (FOS) for Sedimentation <br />Pond 013 using available soil data obtained from soil testing and the pond 012 configuration. <br />1.2 METHODOLOGY <br />The static FOS for the sedimentation pond was estimated using a basic, two-dunensional equilibnum <br />analysis program called SLOPE/\`(/. The FOS deterrtained 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 ue produced by the weight of the embankment and beddutg materials <br />as well as the water volume impounded in the pond. For this analysis, a circular Failure mode vas <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 Eor Sediment Pond 012 as shown <br />on Dtawing 13-6 (I,eidtch, 2000). The section used is also shown in Drawing ]3-G. For the analysts, <br />it was assumed that the water surface behind the embankment was at an elevation equal to 7,254 feet <br />above mean sea level (msl). This water surface elevation is based on the invert of the principal <br />spillway. <br />The embankment 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 21 <br />feet. The upstream height (measured from top of embankment to upstream toe) is approximately 22 <br />feet, with an additional 12 vertical feet of incised excavation. The downstream height (measured <br />from top of embankment to downstream toe) is approximatel}' 21 feet. <br />A phreatic surface was generated based on the permanent water surface elevation of 7,254 ft-msl <br />equivalent to the invert of the principal spillway. The phreauc st¢face through the embankment was <br />estimated based on Darcy's law and observation of strnilar homogenous pond embankment, at the <br />mine site. At these locauons seepage dues not occur above the embankment toe. The resulting <br />surface is shown on the SLOPE/\C~ computer printouts contained in appendix B. <br />Prior to construction, 2 soil samples were collected from the foundation area (G1 and G2) and nvo <br />samples were collected from the borrow areas (G3 and G4). In addition, a soil sample was collected <br />Form the finished embankment. Grain s¢e and atterberg limits were run on all of the samples and <br />the results are shown on Table 1. <br />Sod shear strength propemcs for the pond foundation were detenntned by comparing the index <br />properties (particle sve data and ~\tterberg limits) for the soils a[ the pond location to the index <br />• properties of soils in [he area that have been tesred For shear strength properties. The index tea <br />properties and shear strength values for dre soils tested fur ponds at the sue are shown in "I able 1. <br />rbloon3rrmrq~IFnlmn.-Imeruru. Inr !(i .t~uU~L4r. on BanGrirrd,Surlr-l!0'Ltkezood. ~olnretd~i 80..8'(703):6 3-i l~lp <br />wic~~ ncx~ rn rd,nm :vnN,.,,«imw•,wu,vn r n~ersm ~mo.n e.. <br />•un~nx~ <br />