1991-01-23_REVISION - C1981035

• Permit No: C1981035
• IBM Index Class Name: REVISION
• Doc Date: 1/23/1991
• Doc Name: Adequacy Review
• From: DMG
• To: National King Coal
• Type & Sequence: TR1
• Media Type: D
• Archive: No

STATE OF COLORADO
MINED LAND RECLAMATION DIVISION
� CoLO
Department of Natural Resources
1313 Sherman St.,Room 215
Denver,CO 80203 * .
303 866-3567 #r 1876x
FAX: [phone]
Roy Romer,
Governor
January 23, 1991 Fred R.Banta,
Division Director
Mr, Brad Gosche
National King Coal , Inc. .
P.O. Box 2905
Durango, CO 81301
RE: C-81-035, King Coal Mine TRO1 Adequacy
Dear Mr. Gosche:
The Division Staff has completed the adequacy review of TR-01 (Stipulation 07
for PR-02) and offers the following comments:
The methodology applied by Mr. Johnson consists of a manual evaluation of the
original Terzaghi and Rankine pile stability equations. This technique is
valid, but has several serious constraints which might render it inconclusive
in this situation. The analytical technique graphically divides the body of
the pile into two zones, that portion applying the load acting to displace the
pile, and that zone supplying the resistance to displacement. In its simplest
form, as applied by Mr. Johnson , the technique assumes a level and planar
foundation beneath the pile. In addition, the evaluation of the equations
requires the determination of values for the refuse density, the coefficient
of friction of the waste material , and the angle of repose of the refuse.
Mr. Johnson has uniformly applied a refuse material density of 86
pounds/cubic-foot, a coefficient of friction of 0.93 , and an angle of repose
of 42 degrees. No explanation is provided to document the derivation of these
important mechanical properties for the waste. The applicant should provide a
thorough discussion of the derivation of each of these mechanical properties,
including a discussion of the expected uniformity of these properties
throughout the refuse.
Information derived from the site 's topographic maps and on-site inspections
indicate the foundation of the proposed refuse pile is neither level nor
planar and appears to dip away from the high wall of the face up. This
configuration is not conducive to stable placement of refuse. Further, the
simplistic analysis performed by Mr. Johnson would not be adequate to
determine the projected mass stability of the proposed refuse pile. Since
Terzaghi and Rankine developed the calculation techniques in the early 1900's,
considerably more comprehensive techniques have been developed. Slope
stability analytical techniques , such as the Bishop Method and the Simpson
Method, have been developed which can evaluate the stability of more complex
pile configurations.