PROJ00345

• Contract/PO #: C153330
• Contractor Name: Upper Yampa Water Conservancy District
• Contract Type: Loan
• Water District: 0
• County: Routt
• Bill Number: SB 77-35
• Loan Projects - Doc Type: Feasibility Study

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abutment and 7.3 for the borrow area. (Based on test results in the "Geo-

technic Data".) This tendency toward higher plasticity in the debris flow

material constituting the left abutment is considered favorable as it pro-

vides increased resistance to migration of fines or piping.

Permeability. The gradation, density, and plasticity of the abutment

materials indicate relatively impervious abutments. This is generally con-

firmed by the percolation tests performed in drill holes and test pits, One

possible exception was noted in a percolation test which was in progress on

the right abutment on August 23, A test pit on the dam axis midway up the

abutment was reported to have higher loss rate than others. While test results

have not been reviewed, visual inspection of the test pit indicated local sand

lenses could account for this loss. As the morainal materials are character-

istically unstratified, the possibility of connecting lenses or a continuous

pervious strata through the abutment is remote.

B. Foundation (Valley Bottom)

Density. The geologic history of the damsite as well as the penetration

test data indicate dense foundation materials in the valley floor and a pro-

gressive increase in density with depth. For example, drill hole 102 is logged

showing a blow count of 10 at 10-foot depth, 23 at 25 foot depth, and a con-

tinuing direct relationship between blow count and depth throughout the hole,

These values would correspond to relative densities in the range of 70% to

80% if the materials were primarily granular. If primarily fine-grained, the

soils would be classified as firm,to'very firm., Actual materials probably

contain both granular and fine-grained zones and mixtures of the two. In

any case, the penetration tests indicate more than adequate bearing capacity

for the dam, considering the relatively flat dam slopes,

Gradation, Foundation materials forming the valley floor are apparently

typified by the gradation curve shown in the Geotechnic Data from test pit 105.

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