PROJ00137

• Contract/PO #: C153467
• Contractor Name: Greeley, City of
• Contract Type: Loan
• Water District: 0
• County: Weld
• Bill Number: XB 99-999
• Loan Projects - Doc Type: Feasibility Study

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sand; to ~' = 400 and C' = 0 for the silty sand with gravel. Because of
the granular nature of the materials comprising the embankment, soil cohesion
should not be depended on for shearing resistance. The shear strength
parameters chosen to represent the enti re embankment were ~ 0 = 380; wi th
CO = O.

2.3.4

Failure Surface

There are two common failure surface configurations used for stability
analysis. A circular arc failure surface is more applicable for analyzing
essenti ally homogeneous or zoned embankments, founded on bedrock or thi ck
deposits of fine-grained materials. A non-circular failure surface, described
by linear segments, is generally more applicable for zoned embankments on
foundations containing one or several horizontal or nearly horizontal weak
layers. Non-circular failure surfaces can also be used for relatively
homogeneous dams, which contain continuous well-defined horizontal weak layers.

The failure surfaces shown on Figure V.2 are critical slip planes, located by
a search routi ne in the computer program "PCSTABL5". The top of the sl ip
surfaces were confined to near the dam crest to represent a critical failure
which could result in loss of the reservoir. When the phreatic surface is
modeled as being coincidental with the slope face, smaller failure surfaces
near the toe of the slope may in fact be sl i ghtly more cri ti cal than the
larger surfaces encompassing the entire slope. However, the risk of total
embankment failure as a result of these surficial slumps or ravelling is less
than the risk associated with an entire slope failure.

2.3.5

Results

For the purpose of slope stabil i ty analysi s, the factor of safety is defi ned
as the ratio of total avail abl e shear strength of the soil to shear stress
required to maintain equilibrium along a potential surface of sliding. The
factor of safety indicates a relative measure of stability for various
conditions, but does not precisely indicate the actual margin of safety;

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