2014-11-14_PERMIT FILE - C1996083

Home Browse Search

any HUddleston -Berry s. rrc As part of their work in 2005, Buckhorn installed vibrating wire piezometers and inclinometers in gob pile #2. As a result, based upon the availability of pore pressure and inclinometer data, Buckhorn re- evaluated the stability of gob pile #2 in 2008. At that time, the available data suggested that undrained conditions did not exist within the gob pile. Therefore, Buckhorn completed drained analyses and determined that the upper gob slopes could be increased from 5H:1 V to 3H:1 V. Since 2008, coal mine waste has been placed on gob pile #2 to achieve slopes of 3H:1 V. In 2014, HBET re- evaluated the stability of gob pile #2. The analyses indicated that stockpiling of wet gob on top of gob pile #2 during the winter months would not adversely impact the overall stability of gob pile #2. In addition, the analyses indicated that the gob pile would be stable to a height of 350 feet. 3.0 STABILITY ANALYSES 3.1 General In order to evaluate the stability of the existing gob pile #2, HBET utilized cross sections generated by J.E. Stover and Associates based upon current survey data. The locations of the sections are shown on Figure 1. Analysis of the gob pile was completed utilizing the GeoSlope GeoStudio 2007 SLOPE/W software package. The analyses were completed using the Spencer method which considers both force and moment equilibrium. This is consistent with the recent analyses completed by HBET. 3.2 Soil Parameters Soil parameters used in the stability analyses were selected based upon information in the referenced documents. In general, based upon the referenced reports, the piezometers near the toe of gob pile #2 are showing a steady decrease in pore pressures. In contrast, the piezometers near the top of the gob pile have shown some increases in pore water pressures since installation. These increases are consistent with the loading associated with addition of gob at the top of the pile. However, the elevated pore pressures recorded in the piezometers higher in the gob pile (VWP -06 and VWP -08) are not sufficient to demonstrate undrained conditions in the gob pile. As a result, HBET utilized drained conditions for the analyses. However, the pore pressures should continue to be monitored over time as a sharp increase in the pore pressures over a short time could indicate that undrained conditions are developing which may result in instabilities in the gob pile. The parameters used in the analyses are discussed in the following sections. Compacted Gob The referenced reports indicate that wet unit weights of between 104.6 pcf and 110 pcf have been used in various analyses over the last several years. Based upon previous analyses conducted by HBET, a wet density of 104.6 pcf provides the lowest factor -of- safety. X:2008 ALL PROJECTS \01349 -Bowie Resources, LLC \01349 -0001 Bowie Mine\200 - Geo \Gob 2 \Coverfill Stability \01349 -0001 R091914R2.doc 2