WSP07002

• File Number: 8449
• Description: Platte River Studies
• State: CO
• Basin: South Platte
• Date: 2/1/1991
• Author: City of Greeley
• Title: Feasibility Study for Rehabilitation of Hourglass Dam and Reservoir Vol. 1
• Water Supply Pro - Doc Type: Publication

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with plastic caps. Summary logs of the test holes are shown on Figure 2. Water levels in
the test holes were measured upon completion of drilling, or one day later.

In addition, one sample of potential borrow material was obtained by representatives of the
City. The sample was a composite from four test ptts 1\\ to 2 feet deep, excavated in the
vicinity of Station 10+00, upstream from the embankment. This sampling operation was not
observed by WCC.

5.3.2.2 Laboratory Investigations

Laboratory Investigations were performed to provide Information about the engineering
properties of the soil at the site. Laboratory tests conducted on soil samples for the
feasibility study include gradation, natural moisture content, natural density, Atterberg limits,
specHic gravity, and triaxial shear strength. The results of the laboratory investigations are
presented in Table 1 and Figures 6 through 10.

5.2.3 SUBSURFACE CONDITIONS

The test holes generally showed 11 to 26 feet of embankment material overlying natural soils.
The embankment materials generally consisted of medium dense to dense, slightly silty to silty,
gravelly to very gravelly sands. Laboratory test results show that this material has an internal
friction angle of 39. wtth no cohesion, has a natural dry density of 116 pet, and is non-plastic.

The natural materials below the embankment are glacial deposits which consist predominantly
of loose to medium dense, clean to silty sands with Interlayered sandy silt lenses. Other natural
materials In the embankment foundation range from slightly sandy silts and clays to sandy
gravels with cobbles. The stratigraphy of the natural materials does not correlate well between
test holes. The results of triaxial laboratory testing show that the foundation material has an
internal friction angle of 44' with no cohesion, and has a natural dry density of 125 pet. Most
of the foundation soil samples tested were found to be non-plastic. Atterberg limits tests on
a sample of sandy silt from the foundation show a liquid limit of 37 and a plasticity index of
10.

Bedrock was not encountered in any of the test holes to the maximum depth drilled (80 feet).

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