PERMFILE40184

• Permit No: C1981039
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Doc Name: Pages III-1 through III-62
• Section_Exhibit Name: III. OPERATING PLAN
• Media Type: D
• Archive: No

• The fill material will consist of a sandy gravel. The gravel will
be sandstone; the sands in the gravel will result from partial disin-
tegration of the sandstone during blasting, placement and compaction.
The fill material will be well drained,; a phreatic surface is unlikely
to develop in the fill section.
A dense sandy gravel has a friction angle as high as 50°. In the
loose state this material can have a friction angle as low as 35°(1),
We assumed that the fill material will have a moderate density, 108
pcf, but a low friction angle, 35°. The stability analysis shows that
the factor of safety (F. O. S.) against failure is 1.30, well above the
required F.O.S. of 1.25. The actual fill will probably have greater
strength, resulting in a F.O.S. even greater than 1.30.
The cross-section shown on Figure 5 includes a potential failure
surface which is a thin slice through the surface of the fill slope.
The stability analysis shows the F.O.S. for this surface to be 1.01.
The "failure" suggested by this surface is trivial, consisting of
minor surface sloughing. This failure surface is essentially an infi-
nite slope. Using the infinite slope equation: F.O.S. = tan Qf ,
tan slope
we can determine the friction angle required to reach a F.O.S. equal
to 1.25. That angle is about 40°. Since the actual friction angle
for a sandy gravel will vary between 35° and 50°, depending on
• density, most areas of the fill slope will have a F.O.S. greater than
1.25. Where densities are low, minor surface sloughing may occur.
This area can be repaired as part of the maintenance program, without
endangering the stability of the embankment.
The existing haul roads in the permit area have shown signs of
minor instability in localized areas. All of these unstable areas are
in cut slopes, not fill slopes. The amount of debris resulting from
slides on the cut slopes is not large. It appears that the slides
result from surficial weathering of exposed rock. There is no indica-
tion that the rock is weak at depth; therefore, the possibility of a
deep-seated major slope failure is small. Debris from minor surface
sloughing does not pose a threat to safety; the debris will be removed
as part of the routine maintenance of the road.
To determine the durability of the rock in the haul road
embankment, a Los Angeles abrasion test should be run on a represen-
tative sample of the rock which will be placed in the embankment. We
were able to collect two samples in the field. A sample of sandstone
was collected from an outcrop in the area. Some of the core collected
during drilling of Pit No. 4 was available. This core was from the
overburden or upper interburden rather than the lower interburden
where the rock fill for the road will originate.
• (1) See Table 17.1, pg. 107, Soil Mechanics in Engineering Practice,
Terzaghi and Peck, 1967, Second Edition, John Wiley, New York.
8-81 III-10