C153379 Feasibility Study

• Contract/PO #: C153379
• Contractor Name: Brook Forest Water District
• Contract Type: Loan
• Water District: 9
• County: Jefferson
• Bill Number: SB 80-67
• Loan Projects - Doc Type: Feasibility Study

and the erodability of the clay soil in a recompacted state. Because of the

large amount of silt and sand and smaller amounts of clay in these soils,

erodability was the criteria rather than dispersion.

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Direct shear strength tests were performed on relatively undisturbed

samples of Sand Hills Formation and floodplain alluvium and triaxial strength

tests were performed on compacted samples of remolded Hurley Terrace, Louvier:,

Alluvium, Sand Hills Formation, Fox Hills Formation and Pierre Shale. Direct

shear tests were performed on three relatively undisturbed samples of the Sand

Hills Formation and also on three samples of the floodplain alluvium (Hurley

Terrace). The triaxial tests on recompacted materials were performed 011

samples recompacted to as nearly the same density as possible and at two

different levels of confining pressure. The tests were triaxial consolidated

undrained compression tests with pore pressure measurements. The pore

pressures were measured in the undrained tests to determine the effective

stress strength parameters.

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3. Site Conditions
a. Surface Conditions
The proposed dam alignment as shown on Figure 111-3 and VI-l (Chapter VI)
is approximately 30,000 ft or 5.7 miles in length. The average ground slop,~
along the axis of the dam is on the order of one percent. The maximum height
of the dam (135 to 142 ft) will extend over a 3500 ft length where the
axis crosses the South Platte River valley.

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The surface conditions can be divided into two distinct areas. The first
area is the valley floor of the South Platte River which contains areas 0:[
irrigated and cultivated farmland. The surface soils are highly organic and,
during irrigation, the water level can be at or above the ground surface
(flooded). The second area covers both the left and right abutments of the
dam axis where the surface soils are composed of the Sand Hills Formation.
This formation is an aeolian or windblown deposit that is sparsely vegetated
with natural grasses. The surface sands are fine to medium grain, poorly
graded sands that can be classified as an SM or an SP in the Unified Soil

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III-16

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