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PERMFILE47451
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PERMFILE47451
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Entry Properties
Last modified
8/24/2016 10:49:28 PM
Creation date
11/20/2007 1:10:00 PM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1980007A
IBM Index Class Name
Permit File
Doc Date
12/11/2001
Section_Exhibit Name
Exhibit 51 Lower Refuse Pile
Media Type
D
Archive
Yes
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Mountain Coal Company, LL.C. Exhibit 51 <br />West Elk Mine Lower Refuse Pile <br />In the alluvial soil north of the toe of the pile, the river was assumed to control the position of the water <br />• table. Beneath [he pile, water levels within foundation materials were depicted based on measured levels <br />within piezometers and monitoring wells and conservatively increased (typically 10 feet or more). Within <br />the pile, a second "perched" water table was modeled having a maximum thickness of at least 27 feet as per <br />the results of earlier analyses. The water surface was then assumed to drop into underdrains as it crossed <br />their location. For stability analysis, the presence of the second underdrain near the back of the pile was <br />ignored,maintainingaconservativelyhighwatersurfaceprofile. Specific water surface profiles used in the <br />analyses are found on the appropriatecross-section. <br />5.5.E Analyses Results <br />~, <br />Stability analyses were performed on each of the three cross-sectionsusing both circular and planar failures. <br />In all cases, stability was found to be controlled by circular failures. Both deep and shallow failure circle <br />analyses were performed. The minimum safety factor associated with a deep failure was 1.56 on cross- <br />section E-E'. The additional analysis performed involving the formationof a shallow failure circle through <br />the coal waste material indicated an overall saferv factor of 2.0. In both cases. the model had a saferv factor <br />exceeding 1.~ as required by the CDMG. <br />Critical failure circles and their associated safety factors are shown on the respective cross-sections. In <br />addition, more specific information on analyses results can be found on Table 8. <br />Table 7 - Summary of Stability Analysis Results <br />Cross Deep Failure Shallow Failure Factors of Safety <br />Section <br /> Static Earthquake <br />A-A' x 2?2 1.55 <br /> x 256 1.80 <br />D-D' x 1.89 1.40 <br /> x 1.96 1.52 <br />E-E' x 1.~7 1.14 <br /> x 1.56 1.17 <br />5.6 Slope Stability Analysis of Phase V <br />A slope stability analysis was conducted on the reconfigured Phase V LRP. Previously identified <br />profiles (Section 5.5) were found to have the highest potential for slope failure. These same profiles <br />were analyzed for stability for Phase V. <br />The slope stability analysis utilized the computer program PCSTABLS to determine the factors of safety <br />against failure. The factor of safety is [he ratio of the forces resisting [he slope movement to the forces <br />which cause the slope to fail. The resis[ins forces are determined by the shear strength of [he imported <br />soils to resist failure along a specific surface. The forces which tend to cause failure include, but are not <br />limited to: (a) the ancle of the slope: (b) the location of existing roads, drainage ditches, and sediment <br />control ponds in relation to the slope: (c) pore pressure or water table acting on [he failure plane; and (d) <br />the characteristics of the coal refuse, native soil and bedrock found in the slope. A factor of safety of I.0 <br />21 <br />
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