PERMFILE118853

• Permit No: M2000087
• IBM Index Class Name: Permit File
• Doc Date: 8/24/2000
• Doc Name: MEMO STABILITY ANALYSIS FOR MILLIKEN PIT APPLICATION M-2000-087
• From: DMG
• To: TOM SCHREINER
• Media Type: D
• Archive: No

iii iiiiiiiiiiiu iii
999 .
• STATE OF COLORADO i
DIVISION OF MINERALS AND GEOLOGY ~
Department of Natural Resources
1313 Sherman St., Room 215
DIVISION O F
Dem•el, Colorado 80203 MINERAL S
Phone: [phone]
FAX: [phone] &
GEOLOGY
R E C L A M A T I O N
MINING•SAFETY
Bil I Owens
MEMO ~o,-ernor
DATE: August 24, 2000 ereg t. warner
TO: Tom Schreiner E>ecuuve DireUOr
Ce: Carl B. Mount Michael B Lang
Division Direaor
FROM: Christina KamnikarC~
RE: Stability Analysis for Milliken Pit application, #M-2000-087
Having reviewed the stability analysis for this project, I found several gaps in the document that need to be
remedied before this stability analysis can be accepted as technically adequate. These include the following:
1) A copy of the data input for the factor of safety calculations. This would include the strength,
cohesiveness, and internal angle of friction for the soils as inputted into [he software program, as well as
which analysis, Spencer or Bishop, was used, and whether any internal or external loading was applied or
friction factors inputted.
2) What is the slurry wall thickness? This is stated nowhere in the document, and the validity of the results
can not he checked without [his information.
3) Will [he site be dewa[ered through in-place wells, or with a dewatering trench a[ the toe of [he slope? How
far away will these wells or trenches be from the excavation slope?
4) How were [he soil parameter values for [he "mud lens'" layer arrived a[? This is not a ASTM classification
for soils. Please explain how [his label was applied.
5) How far away is the irrigation ditch 'immediately to the west of the mine? At this point, several
structures are within 10' to 30' away from the slurry wall.
6) Finally, how will the slope of 2H:1 V be guaranteed? What equipment will be used [o excavate this slope?
It might be wiser to calculate a minimum setback from the edge of the excavation face to the slurry wall,
and maintain that setback, the excavation slope allowed to retain whatever grade is convenient for the
operation.
While the preliminary analysis indicates that mining at an angle of 2H:1 V with a 20' setback from the slurry
wall does guarantee a minimum factor of safety of I.S, this analysis can not be considered final until the above
questions are answered, and the data results reexamined in light of the new information.
Until these questions are answered, this stability analysis can not be accepted as it is.
C.L. Kamnikar