REV06652

• Permit No: C1980007
• IBM Index Class Name: Revision
• Doc Date: 2/18/1992
• Doc Name: WEST ELK STACKER TUBE PN C-80-007 TR 61
• From: MLRD
• To: CHRISTINE JOHNSTON
• Type & Sequence: TR61
• Media Type: D
• Archive: No

STATE OF COl~ll IIIIIIIIIIIII III
MINED LAND RECLAMATION DIVISION
Department of Natural Resources
1313 Sherman St., Room 275
Denver, CU 80203
303 866-3567
Fax. [phone]
Date: February 18, 1992
To: Christine Johnston
Fr: Bruce Stover //LC'~C~Z.
Re: West Elk Stacker Tube, Permit C-80-007 Technical Revision No. 61
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Roy Romer.
Governor
Fred R. Banta.
Division Director
I received your request for clarification of my memo regarding the stability
analysis on the West Elk Stacker Tube Technical revision. The stability
analysis presented for the proposed use of coal waste (gob) in the foundation
for the stack tube pile indicates that the foundation can be constructed to
meet the minimum required safety factor of 1.3. This assumes that materials
having the geotechnical strengths ae stipulated in the analysis are used, and
placed and constructed as shown in the design.
As indicated in the submitted geotechnical data, coal waste materials can vary
widely in strength parameters. Some types of coal waste can have strengths
significantly below the values assumed in the design of the stack tube
foundation. It therefore is critical that careful control of the coal waste be
exercised so that low strength materials are not incorporated into the
foundation voile. This is also true for the compacted clay soil toe buttress
called for in the design. Geotechnical testa of the actual coal waste and clay
soil materials to be used in the foundation should be made to ensure that
materials meet the the strength parameters assumed in the stability analysis.
A geotechnical engineer should supervise construction of the stacker tube
foundation to ensure that the selected materials are placed, compacted, and the
foundation constructed as designed.
The bottom line is that if the stacker tube foundation is constructed using
materials having appropriate strengths, and to the specifications of the
at ability analysis, the structure should meet the minimum factor of safety of
1.3. If lower strength materials are used, or if the materials are not
properly placed and compacted, failure of the stack tube coal pile foundation
could result if the ae-built factor of safety is too low. In approving the
Technical Revision, you may wish to require the engineering checks discussed
above to certify that the foundation is constructed as proposed.