C150063 Feasibility Study

• Contract/PO #: C150063
• Contractor Name: Jackson Lake Reservoir & Irrigation Company
• Contract Type: Loan
• Water District: 1
• County: Morgan
• Bill Number: SB 94-29
• Loan Projects - Doc Type: Feasibility Study

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dam. It was determined that the cutoff wall at the upstream toe was very
shallow, ranging from about 10 inches (the approximate thickness of the
underlying slabs) to about 24 inches deep. The conclusion formed is that
there is minimal seepage cutoff between the lake and the embankment
materials, except in areas where the beach sands have overlain the upstream
facing to some degree.

During the investigation, approximately 57 test pits were excavated for
evaluation of the lakebed material suitability as an aggregate source for soil
cement. Two types of material were identified: clean to slightly silty sand in
the lake bed away from the dam (Set 1), and clayey sand from samples
located near the dam and spillway (Set 2). Detailed laboratory evaluations
for soil cement design and the suitability of the aggregate in soil cement
shows that the Set 1 materials were suitable at 10 percent cement content.
Using the Portland Cement Association (PC A) short cut test, the Set 2
materials were tentatively identified as requiring from 11 to 1 3 percent
cement to form a soil cement equivalent to the Set 1 materials.

Sufficient quantities of suitable soil cement aggregate were identified ;n close.
proximity to the dam, making soil cement an economically viable repair
material.

In the fall of 2000, Kumar and Associates evaluated the slope stability of the
existing embankment and potential for liquefaction of the embankment under
earthquake loading. Using information obtained from the previous Kumar
studies and from the Smith 1 993 report, certain assumptions were made as
to embankment soils friction ang.les and cohesion. The analyses showed
that the existing embankment is marginally stable. The factors of safety
determined for the several assumed loading conditions are presented in
Table 6. The existing embankment appears the have an inadequate factor of
safety for several loading conditions of the upstream slope. Any contribution
of the existing slabs to overall stability was neglected. Also evaluated was

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