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Huddlestan-Betty <br />k r;,�n�: -pA Ulk, LLC <br />3.0 STABILITY ANALYSES <br />3.1 General <br />In order to evaluate the stability of the existing gob pile 91, HBET utilized cross <br />sections generated by Stover based upon current survey data. The location of the section <br />is shown on Figure 1. Analysis of the gob pile was completed utilizing the GeoSlope <br />GeoStudio 2007 SLOPE/W software package. The analyses were completed using the <br />Spencer method which considers both force and moment equilibrium. This is consistent <br />with the recent analyses completed by HBET. <br />3.2 Soil Parameters <br />Soil parameters used in the stability analyses were selected based upon our <br />experience and information in the referenced documents. However, the analyses <br />completed by WESTEC and Lambert used dramatically different soil parameters. Based <br />upon our experience with gob pile #2 and gob pile #3, the coal waste soil parameters for <br />these areas are fairly well defined. However, Stover indicated to HBET that the coal <br />waste material at pile #1 is significantly different than the coal waste placed at pile #2 <br />and pile #3. The gob at pile #1 was not produced from the wash plant. It is much coarser <br />material with a significant quantity of larger particles (gravel, cobbles, etc.). Therefore, <br />the shear strength of the material at gob pile #1 would be expected to be higher than at <br />pile #2 or pile #3. Given that the material at pile #1 was placed over 10 years ago, <br />HBET believes that drained conditions will prevail at this location. The parameters used <br />in the analyses are discussed in the following sections. <br />Compacted Gob <br />In order to evaluate impacts on the stability of gob pile #1 from the variability in <br />the soil parameters used by WESTEC and Lambert, HBET conducted preliminary <br />stability analyses using the WESTEC parameters and Lambert parameters. The <br />foundation soils at gob #1 are generally the same as at gob #2 and gob #3. Therefore, the <br />foundation soil parameters used in previous analyses for gob #2 and gob #3 were used in <br />the current analyses. <br />The results of the preliminary analyses indicated the following Factors of Safety <br />(F.S.). The results are included in Appendix A. <br />• WESTEC Soil Parameters —minimum FS = 2.837 <br />• Lambert Soil Parameters — minimum FS = 1.935 <br />Both sets of soil parameters resulted in F.S. much greater than 1.5. However, one <br />of the significant variations between the two sets of parameters was the unit weights used <br />by WESTEC and Lambert. The February 1999 report by Lambert included moisture <br />content and density data collected from borings conducted at gob pile 91. The data <br />shows a range of dry densities of between 58.6 pcf and 97.6 pcf for the gob. Using the <br />moisture content data, this corresponds to moist unit weights of between 64.3 pcf and <br />110.7 pcf. The average of all of the testing on the coal waste material at gob #lwas 93.5 <br />pcf. <br />X:\2008 ALL PROJECTS\01349 -Bowie Resources, LLC\01349-0001 Bowie Mine\200 - Geo\Gob 1\01349-0001 R112114.doe 2 <br />