APPCOR11629

• Permit No: C1981020
• IBM Index Class Name: Application Correspondence
• Doc Date: 2/4/1982
• Doc Name: REVIEW OF THE GEOTECHNICAL ASPECTS OF THE MUNGER CANYON COAL MINES SUPPLEMENTAL PERMIT SUBMITTALS
• From: MLRD
• To: JIM PENDELTON
• Media Type: D
• Archive: No

• _2_ •
Rule 4.03,I(3)(d)(ix) requires that no haul road fill embankment exceed a slope
of 2:1 (horizontal to vertical), unless the applicant demonstrates that the
steeper proposed embankment will be stable. All fill embankments proposed within
the application are specified as having slopes of 2:1, and are, therefore, in
compliance with the permanent regulations.
Rule 4.03.1(3)(e)(i) requires that no haul road cut slope exceed a slope of 1.5:1
(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, That rule states; "...except
that steeper slopes may be specifically authorized by the Division if geotechnical
analysis demonstrates that a minimum safety factor of I.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 2.2-16 through
2.2-23)
Station 72+70'
Station 82+25'
Station 85+75'
Station 88+40'
Station 95+00'
Station 101+00
through 75+50'
through 83+60'
through 87+25'
through 95+00'
through 101+00'
' through 104+30'
The geological mapping included within Exhibit O, the report prepared by Geo-
Hydro Consultants, Fnc., indicated that each of the above-listed cut slopes will
be excavated in materials which were mapped as unconsolidated soils. (See geo-
technical map, Sheet 1, 2 and 3, Exhibit O) The applicant proposes to excavate
these soils to finish slopes of roughly l:1 (horizontal to vertical). Slope
heights will reach I35 feet. Slopes which exceed 60 feet in vertical height are
designed with a 15 foot wide intermediate terrace bench, which will result in
overall slope gradients between 1.1:1 and 1.2:1 (horizontal to vertical) for the
affected cut slopes.
Pursuant to Rule 4.03.I(3)(c)(i), the applicant may pursue two courses of action
in order to obtain approval of these steep cut slopes. The applicant may complete
a mathematical stability analysis, based upon appropriate material strength data,
to demonstrate the static slope safety factor of the designed cuts will exceed 1.5.
Such an analysis could consider worst-case situations characteristic of the materials
and cut slope configurations proposed within the plan. Alternatively, the
applicant may choose to demonstrate, through appropriate geotechnical analysis,
"...that a safety factor of less than 1.5 will not result in significant environ-
mental harm or harm to the public health and safety." Such a demonstration should
include, at a minimum, a thorough geotechnical discussion of worst-case potential
slope failures and their potential environmental and public health and safety
impacts, Further, that discussion should describe why the applicant considers
these potential impacts to be insignificant. If potentially significant environ-
mental or public health and safety impacts are determined to exist, the applicant
may consider techniques of mitigation to abate these significant impacts.