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• <br />Aasumsd Incrsesed phreatic <br />surtace for ~enattlvNy anelyaea <br />:,. _r . ' -'%T-' _°- - rJo ~ Sao ' -_~ .v~ -_~-_- - _. Zu - me quo: _. _ .. .,x. __ <br />Figure 3. Phreatic surfaces used for the stability analyses. The lower phreatic surface is based on pore <br />• pressure measurements from the installed vibrating wire piezometers while the upper <br />phreatic surface is an assumed increased surface in order to evaluate the model sensitivity to <br />pore pressure increases. <br />It is worth noting that geotechnical investigations previously conducted at this site did not <br />encounter groundwater in the foundation soils (BGI, 2006 and Lambert, 2003). Nonetheless, <br />foundation underdrains were constructed prior to waste placement as part of the Detailed <br />Design, Construction, Operation, and Reclamation Plan (J.E. Stover and Associates, 2003). <br />Consequently, development of shallow groundwater in the foundation soils is very unlikely. <br />5.4 Stability Evaluations <br />Stability of the coal mine waste pile was evaluated using two-dimensional limiting equilibrium <br />stability analyses with the computer software SLIDEdeveloped by Rocscience (2004). Critical <br />factors of safety are calculated by SLIDE by comparing the available shear strength of the soil <br />or rock to the equilibrium shear stress in the soil/rock. Spencer's method was used for the <br />analyses. In accordance with DRMS (2005), only static conditions were evaluated. <br />Search methods employed by SLIDE examine tens of thousands of potential failure surfaces for <br />each analysis. The factors of safety for critical circular and non-circular (block-type) failure <br />surfaces are presented in Table S. Output from critical stability analyses is presented in <br />Appendix D. <br /> <br />kluw,c No ? 2UU~ Itee~ aluuon of Coal ~1ine 14 ate titabiGtv.doc <br />Nagc' I Z of 1 <br />