Laserfiche WebLink
(D -;)Huddleston -Herr• <br />The evaluation was completed by a Colorado registered professional engineer in <br />accordance with generally accepted geotechnical engineering practices. This report has <br />been prepared for the exclusive use of Bowie Resources, LLC. <br />2.0 BACKGROUND <br />The available reference documentation indicates that the original geotechnical <br />investigation was completed by Lambert and Associates (Lambert) in 2003 and that <br />placement of coal mine waste at gob pile #2 began in 2004. Additional evaluation of the <br />stability of gob pile #2 was completed by Lambert and Buckhorn Geotech, Inc. <br />(Buckhorn) in 2005. Based upon the results of these analyses, maximum slopes of <br />5H:1V were specified for gob pile #2. However, this was based upon the assumption that <br />undrained (total stress) conditions would exist within the gob pile. <br />As part of their work in 2005, Buckhorn installed vibrating wire piezometers and <br />inclinometers in gob pile #2. As a result, based upon the availability of pore pressure and <br />inclinometer data, Buckhorn re-evaluated the stability of gob pile #2 in 2008. At that <br />time, the available data suggested that undrained conditions did not exist within the gob <br />pile. Therefore, Buckhorn completed drained analyses and determined that the upper gob <br />slopes could be increased from 5H:1 V to 3H:1 V. Since 2008, coal mine waste has been <br />placed on gob pile #2 to achieve slopes of 3H:1 V. <br />Buckhorn's 2008 analysis included evaluating an increase in the final buildout <br />height of gob pile #2 from 240 feet to 300 feet. However, HBET understands that gob <br />pile #2 is currently proposed to be extended to a final buildout 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 a cross <br />section generated by J.E. Stover and Associates based upon available survey data and <br />proposed buildout configuration. Analysis of the gob pile was completed utilizing the <br />GeoSlope GeoStudio 2007 SLOPE/W software package. <br />During our review of the available documentation, HBET observed that some of <br />the previous analyses were completed using Spencer's method. However, some of the <br />analyses were completed using the simplified Janbu method. The simplified Janbu <br />method does not consider both force and moment equilibrium whereas the Spencer <br />method does. In general, HBET believes that the Spencer method is mathematically <br />more robust and provides a more accurate assessment of stability of slopes. As a result, <br />HBET used the Spencer method in our analyses. <br />X %2003 ALL PROIEC 1S 00489 - JE Storer Associates Inc' 00489-0003 Buisie Mint'200 - Gto Gob 2'Full Buildout 00739-0003 R073014 duc 2 <br />