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REV01282
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REV01282
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Entry Properties
Last modified
8/25/2016 12:58:53 AM
Creation date
11/21/2007 8:51:28 AM
Metadata
Fields
Template:
DRMS Permit Index
Permit No
C1980007
IBM Index Class Name
Revision
Doc Date
5/24/1985
Doc Name
MT GUNNISON NO 1 MINE PERMIT C-80-007 -UPPER WASTE PILE PERMIT REVISION
From
MLRD
To
SUE MOWRY
Type & Sequence
PR2
Media Type
D
Archive
No
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-2- <br />DRAFT GEOTECHNICAL FINDINGS <br />MT. GUNNISON N0. 1 UNDERGROUND COAL MINE <br />PERMIT REVISION APPLICATION - UPPER WASTE ROCK PILE <br />Coal Processing Waste and Non-Coal Processing Waste <br />West Elk Coal Company applied for a permit revision to allow the construction <br />of an upper waste rock pile in October of 1984. The operator had noted its <br />intention to construct an upper waste pile in the original permit <br />application. The permit revision application represented the submission of a <br />detailed engineering plan for that structure, for which a general plan had <br />earlier been submitted. <br />West Elk Coal proposes, within the amended permit revision application, to <br />construct a five million ton coal processing waste pile. The refuse will <br />consist of coarse coal reject and development waste rock. The mine projects <br />waste production at a rate of 150,000 tons for the first year and 100,000 tons <br />per year thereafter. The completed waste pile structure will cover <br />approximately 40 acres, and attain a maximum thickness of 160 feet. <br />The waste pile will have 2.5 H:1V (horizontal to vertical) facial slopes with <br />30 foot wide benches at 50 foot vertical intervals. The overall final facial <br />slope will be approximately 3 H:1V (horizontal to vertical slope of <br />approximately 18.2 degrees) in order to facilitate reclamation. Samples of <br />currently produced waste were collected and tested, in order to provide <br />material properties for a mathematical stability analysis. Samples were also <br />collected and tested of subgrade colluvium and bedrock for the same purpose. <br />The stability analysis projected a minimum static slope safety factor of 1.64 <br />for an overall facial slope of 2.5 H:1 V, steeper then the requested <br />configuration. <br />At the request of the Division, West Elk Coal Company also completed an <br />analysis of the potential stability effects upon the F-Seam, from the <br />placement of a five million ton surcharge load upon the existing workings <br />within the mine. The plan calls for approximately the eastern half of the <br />waste pile to be undermined. In completing this analysis, the operator <br />assumed: <br />1. An ultimate configuration of the waste pile reaching elevation <br />6,880 feet above sea level. <br />2. No secondary extraction beneath the pile. <br />3. No barrier pillars, even though one is planned. <br />4. A continuous crack existing from the elevation of the F-Seam's <br />floor to the ground surface at the top of the pile. <br />Two separate conservative strengths were assumed for the floor clay beneath <br />the F-Seam (angle of internal friction = 90, cohesion = 1,350 lbs per square <br />foot: angle of internal friction = Oo, cohesion = 4,320 lbs per square <br />foot), resulting in safety factors greater than 1.62. <br />
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