GENERAL32617

• Permit No: C1981020
• IBM Index Class Name: General Documents
• Doc Date: 9/7/1982
• Doc Name: PROPOSED DECISION AND FINDINGS OF COMPLIANCE
• Permit Index Doc Type: Findings
• Media Type: D
• Archive: No

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Geo-Hydro's report contains the statement; "If our recommendations are accepted,
the cuts will probably be stable for the lifetime of the mine; sloughing will
have to be expected and maintenance of the road will be required." The applicant's
consultant has determined those cut slope gradients which should be stable
during the operational life of the mine. In other words, the consultant has
deduced what cut slope gradients for each characteristic soil or bedrock type
encountered will assure a cut slope with a static slope safety factor which
exceeds 1.0. The applicant's consultant did complete a mathematical stability
analysis of the cut slopes or fill embankments proposed to accommodate the
enlarged haul road.
Rule 4.03.1(3)(d)(ix) requires that no haul road fill embankment exceed a slope
of 2:I (horizontal to vertical), unless the applicant demonstrates that the
steeper proposed embankrrent will be stable. R11 fill embankments proposed
within the application are specified as having slopes of 2:I and are, therefore,
in compliance with the permanent regulations.
Rule 4.03.1(3)(c)(i) requires that no haul road cut slope exceed a slope of 1.5:I
(horizontal to vertical) in unconsolidated materials or a slope of 1/4:1
(horizontal to vertical) in competent rock. Rule 4.03.I(3)(c)(i) does, however,
allow for slopes in excess of the stated maximums. The rule states; "...except
that steeper slopes may be specifically authorized by the Division if geotechnical
analysis demonstrates that a minimum safety factor of 1.5 can be maintained or
if geotechnical analysis demonstrates that a safety factor less than 1.5 will not
result in significant environmental harm or harm to the public health and safety."
Close scrutiny of the applicant's proposed alignment and grading of the haul road
corridor has determined that the cut slopes proposed at various locations between
the design survey stations listed below exceed the allowed maximum slope gradients
for cut slopes constructed in unconsolidated materials (see Figures 2.2-I6
through 2.2-3).
Station 72+70'
Station 82+25'
Station 85+75'
Station 88+40'
Station 95+00'
Station 101+00
through
through
through
through
through
' throng;
75+50'
83+60'
87+25'
95+00'
101+00'
x 104+30'
The geological mapping included within Exhibit 0, the report prepared by Geo-
Hydro Consultants, Inc. indicated that each of the above-listed cut slopes will
be excavated in materials which were mapped as unconsolidated soils. (see geo-
technical map, sheets 1, 2 and 3, Exhibit 0 of the application.) The applicant
proposes to excavate these soils to finish slopes of roughly 1:1 (horizontal to
vertical). Slope heights will reach 135 feet. Slopes which exceed 60 feet in
vertical height are designed with a ZS foot wide intermediate terrace bench,
which will result in overall slope gradients between l.l:l and 1.2:1 (horizontal
to vertical) for the affected cut slopes.