Laserfiche WebLink
Bowie No. 2 Mine C 1996083 Technical Revision No. 84- Second Adequacy Review Page 10 of 15 <br />Density <br />Quarterly reports indicate that the emplaced coal mine waste consistently meets the requisite minimum level <br />of compaction: 90% of the standard Proctor. In 2013, only 6 tests, out of 196 failed this requirement and <br />required reworking, and the average level of compaction was approximately 94.5 %. This represents an <br />improvement over 2012, when the average compaction was 92.7% and reworking was required for 15% of the <br />tests. <br />Moisture Content <br />The ability to achieve compaction is closely tied to the moisture content of a material. The closer the material <br />is to the "optimum" moisture content (OMC), as determined in the laboratory, the easier it is to compact the <br />material in the field. <br />Buckhorn's recommendations regarding moisture content include the following: <br />• Feb -2006 Section 7.0 <br />"It must be emphasized that pore pressures are a crucial component of the stability of the gob stockpile. <br />Due to the fines content of the gob material, pore pressure dissipation is anticipated to be a slow process. <br />Therefore, it is critical that gob materials are not placed wet of the optimum moisture content." <br />• Feb -2007 Section 6.0 <br />"It is critical that gob materials are not placed wet of the optimum moisture content." <br />• Mar -2007 Section 6.0 <br />"Gob must be placed at, or slightly below its optimum moisture content. Gob placed significantly above <br />the optimum moisture content likely will not achieve adequate compaction or undrained shear strength. <br />Placement techniques that allow for drying gob may be required at times," and "On -going <br />moisture /density testing and strength testing of gob are recommended... We also recommend <br />implementation of a moisture content specification allowing moisture contents no greater than 4% above <br />the optimum moisture content as determined by the standard Proctor." <br />• Sep -2008 Section 6.0 and May -2009 Section 6.0 <br />"Proper management of coal waste moisture content during placement will reduce the pore pressures <br />within the fill and enhance stability. As practical, waste materials in excess of the optimum moisture <br />content should be allowed to dry prior to placement. Blending wet material with drier material may also <br />prove to be an effective moisture content management strategy." <br />Quarterly reports indicate that the moisture content of the coal mine waste is consistently well above OMC. <br />In 2012, the moisture content of the coal mine waste was an average of 3.5% above optimum; two of every <br />five tests showed that the moisture content was exceeded by more than 4 %. Significant improvements were <br />made in 2013, with the average moisture content being reduced to only 2.2 percent above optimum. <br />However, moisture contents continued to exceed optimum by more than 4% one out of every five tests. <br />MATERIAL PROPERTIES <br />Native soils were sampled and tested in 2006 for TR -44 (Gob Pile #4) and TR -45 (Gob Pile #3). This level of <br />testing is likely sufficient for the future. <br />Coal Mine Waste was sampled from Gob Pile #2 for TR -42 (in 2005) and TR -44 (in 2006). Other than the <br />ongoing compaction testing, no new tests, specifically triaxial compression tests, have been performed on the <br />CIRCES Cost Estimating Soffi are <br />