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a.3 Sl.oPl= STABiuTr <br />A slope rtabaty analyse was performed fa the coal mine waste bank to ensuro static stability <br />with a brtg~tsrm factor of safety of 1.5 (Ruk 4.10.41211. Stability analyses were performed <br />using computer software calbd PCSTABL Version BH, produced by Purdue University (Purdue <br />University, 19881. Moment equilibrium wss determined using the Modred Bishop Method. <br />A seismic stability analysis also was performed to ensure stability during seismic boding <br />conditions. Apseudo-static factor was added in the horizontal dfreetion to the slide mass to <br />model an earthquake occurtirq in the area. The pseudo-static factor is based om seismic data <br />obtained through the National Oceanic and Atmospheric Association (NOAA, 1994), and was <br />determined to ba 0.1g. Both the static and pseudo-static analyses were conducted modeling <br />the coal mine waste bank at maximum height. Output from the computer analyses is <br />presented in Appendix 0. <br />4.3.1 Groundwater Condrftons <br />Groundwater wndrtiorts at the site wero modeled aocordlrp to the piezometer bated in WBH- <br />S01 in the West Storage Yard, east of the coal mine waste bank. The groundwater was read <br />to be 50 feet bga and is suspected to be remnants of drilling fluid. The phrsatic surface as <br />~~ modeled wsa assumed to run along the coal mine waste bank-collwium interface to the <br />ground surface rt the toe as a conservative measure, ea shown in F figures 4.3 and 4.4 instead <br />of at the observed piezometer bvel. A phreadc surface within the coal mine waste bank is not <br />expected to develop, considering the placement of dry coal mine waste, the planned <br />underdrain system, and the surface runoff diversion systertu designed to route rainwater <br />directly off the coal mine waste before it can infiltrate. <br />4.3.T Material PrapartNe <br />Material propertisa ware dstemlited usirq various mstttods. 8orehok tnvestigationa conduced <br />by W ESTEC, and laboratory analysis on potential coal mine waste material that would be <br />placed it the waste bank, obtained from OXBOW, were used to determine properties. Figures <br />4.3 and 4.4 show a summary of material properties used for tM stability arlafyssa. Material <br />properties required for analysis are Coubmb strength parametero: internal arlgie-of-friction, <br />cohesion, and unit weight. <br />•~ <br />96266/1424.RPr Cod Mir W~~a 9~NC IHtipn fa ttr S~nbatn CrNk MM <br />OetoWr 199e WE67'EC. Iro. 19 <br />