REV95899

• Permit No: M1994117
• IBM Index Class Name: Revision
• Doc Date: 8/5/1998
• Doc Name: FAX COVER
• From: MCCULLEY FRICK & GILMAN INC
• To: DMG
• Type & Sequence: TR3
• Media Type: D
• Archive: No

AUG-05-66 03:52PLt FROMFMcCULLEYF°' KBGILttAN 3034471836 •
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Memorandum
T-000 P.02/03 F-576
4900 Pean East Circle
Swte 300W
Boulder, CO 80301
[phone]
TO: Christina K. Kamnikar - Colo_ Dlv. of Minerals and Geology
CC: Maxine Stewart - ITEC
Ted Gengler
FROM: Larry Owen -MFG Boulder
DATE: August 5, 1998 PROJECT NO.: 5461
SUBJECT: Cash Mine /Gold Hill Mill -Tailings Impoundment Expansion
Geotechnical Investigation
A.
In response to your question, during our meeting this afternoon, regarding our decision to
not conduct triaxial shear tests on the tailings samples collecteq during our site investlgadon, I
woultl like to offer the explanatory comments. Our decision resulted from consideration of a
number of factors, including the following:
Due to the relatively high in situ moisture content of existing tailings, we concluded that it
would be difficult to collect a sample that would remain undisturbed and be representative
of actual conditions.
The beach tailings upon which the embankment raise is to be amsuucted consist primarily
of the sand-sized fraction (See Table C-2. Samples SH-1 and SH-2) and, as such, are
expected to drain relatively quickly (essentially within the con~uuction period) under the
surcharge load of the new embankment fill. Therefore, the n:sults of tests of a drained
triaxial test with pore pressure measurements, conducted on samples of existing materials,
would be valid for only in the short-term.
Almost immediately upon completion of construction, new tailings will be deposited on top
of the existing tailings and against the toe of the new embankment face. These new
tailings will ad as a toe berm to buttress the existing tailings and the upstream face of the
embankment rase, to a progressively increasing extent, and correspondingly enhance the
stability of the system.
0
Any potential failure surface through the embankment raise and the underlying tailings
would be intercepted by the geogrid reinforcement layer that will be placed on the surface
of the tailings prior to crommencing construction of the raise. fhe strength that would be
gained through the presence of the geogrid was not taken into account in the stability
modeling that we conducted.
Very conservative materials properties were attributed to the tailings for purposes of our
stability analyses. Recent results of triaxial testing wnducted c>n similar tailings materials
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