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➢ Control of drainage on and around the stockpile. Care should be taken so as to not <br />allow additional water to infiltrate the gob stockpile. Upgradient surface water should be <br />diverted around the stockpile, and the stockpile should be graded to shed precipitation. <br />5.2 Inclinometers <br />At the writing of this report, baseline readings and one subsequent reading have been taken on <br />each inclinometer. Displacements of the inclinometer casing are calculated by comparing <br />changes in the position of the inclinometer casing relative to the baseline reading. Baseline <br />readings were taken on August 10, 2005 and subsequent readings were taken on November 29, <br />2005. The next set of readings is scheduled for early March 2006. <br />Incremental and cumulative displacements were plotted at two -foot increments along the entire <br />depth of the inclinometer. These plots are presented in Appendix F. Displacements are along <br />the "A- Axis ", oriented in the direction of anticipated movement. Incremental displacements are <br />displacements at discrete depths. A spike in the data growing with time indicates movement at <br />the indicated location of the inclinometer. Cumulative displacements are the sum of incremental <br />displacements relative to the bottom of the inclinometer. Displacements indicated on the plots <br />for the upper six feet of the inclinometer are due to wobbling of the portion of casing above <br />grade, and are considered to be a reading error. The results to date do not indicate any definite or <br />significant movement. We recommend continued monitoring of the inclinometers every three <br />months. <br />6.0 STABILITY EVALUATIONS <br />Slope stability of the coal waste stockpile was evaluated using two- dimensional limiting <br />equilibrium stability analyses with the computer software SLIDE developed by Rocscience <br />(2004). This program utilizes slope geometry, soil and rock strength parameters, groundwater <br />conditions, and external loading to determine theoretical slope stability. Stability is indicated by <br />a ratio of the available shear strength of the soil to the equilibrium shear stress in the soil. This <br />ratio is termed the "factor of safety" with respect to failure. A factor of safety of 1.0 implies the <br />stresses in the soil are equal to the available shear strength of the soil, and slope failure is <br />imminent. <br />Both total and effective stress analyses were conducted and both drained and undrained <br />conditions were evaluated for long term and short term stability. Stability of the gob pile was <br />evaluated for the maximum section (through the approximate central portion of the stockpile) as <br />indicated on the attached Site Plan (Appendix A). The maximum section is considered to <br />represent the likely worst case scenario with respect to slope geometry due to the maximum <br />height of waste. Geometry of the waste stockpile for the analyses was as follows: <br />➢ A slope of 2.5H:1 V (horizontal:vertical) for the first 50 vertical feet of the stockpile <br />(beginning at the toe). <br />➢ A 20 -foot wide bench at a vertical height of 50 feet. <br />Bowie No 2 Gob Pile Stability Dec2005 <br />Project #05- 126 -GEO <br />Page 13 of 18 <br />