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`.��i EIuJJk'�rlsrj- fiirri <br />As pert of their work in 2005, Buckhorn installed vibrating, wire piezolneters and <br />inclinometers in gob pile #2, As a result, based upon flee availability of pore pressure and <br />inclinometer data, Buckhorn re-evaluated the stability of gob pile #2 in 2003. At that <br />time, the available data suggested that undrained conditions did not gist within the gob <br />pile. Therelore, Buckhorn completed drained analyses and determined that the upper gob <br />slopes could be increased from 514:1 V to 3H:1 V. Since 2003, coal mine waste has been <br />placed on gob pile 42 to achieve slopes of 3H:1 V. <br />In 2011, HBET re- evaluated the stability of gob pile #2. The analyses indicated <br />that stockpiling of wet gob on top of gob pile #2 during the winter months would not <br />adversely impact the overall stability of gob pile #2. In addition, the analyses indicated <br />that the gob pile would be stable to a height of 350 feet. <br />3.0 STABILITY ANALYSES <br />3,1 General <br />In order to evaluate the stability of the existing gob pile #2, HBET utilized cross <br />sections generated by J.E. Stover and Associates based upon available survey data. The <br />locations of the sections are shown on Figure 1. Analysis of the gob pile was completed <br />utilizing the GeoSlope GcoStudio 2007 SLOPEIW software package. The analyses were <br />completed using the Spencer method which considers both force and moment <br />equilibrium. This is consistent with the recent analyses completed by HBET. <br />3.2 Soil Parameters <br />Soil parameters used in the stability analyses were selected based upon <br />information in the referenced documents, In general, based upon the referenced reports, <br />the piezometers near the toe of gob pile #2 are showing a steady decrease in pore <br />pressures. In contrast, the piezonaeters near the top of the gob pile have shown some <br />increases in pore water pressures since installation, These increases are consistent with <br />the loading associated with addition of gob at the top of the pile, However, the elevated <br />pore pressures recorded in the piezometers higher in the gob pile (V WP -06 and VWP -03) <br />are not sufficient to demonstrate undrained conditions in the gob pile. As a result, HBET <br />utilized drained conditions for the analyses. However, the pore pressures should continue <br />to be monitored over time as a sharp increase in the pore pressures over a short tulle <br />could indicate that undrained conditions are developing which may result in instabilities <br />in the gob pile, <br />The parameters used in the analyses are discussed in the following sections. <br />Compacted Gob <br />The referenced reports indicate that wet unit weights of between 101.6 pef and <br />110 pcf have been used in various analyses over the last several years. Based upon <br />preliminary sensitivity analyses conducted by HBET, a wet density of 101.6 pef provides <br />the lowest factor -of- safety. <br />N -2006 ALL PROJECTS 01 tag .Bowie Reroulces, LLC - 01.349,0001 Bowie \fine200 2 <br />