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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internal fri cti on for the dam material of 35 to 40 degrees, wi th mi nimal
cohesion. The coefficient of permeability of a typical embankment sample was
5 x 10-5 cm/see., consi stent with the results of the fi el d permeabi li ty
tests.

Potential RCC aggregate included materials comprising the existing dam and
upper reservoi r gl aci a 1 till deposi ts. A set of six RCC test cyl i nders were
cast from unprocessed embankment materi al s (test pit TLP-51, using a cement
content of 150 1 b/cy. Compressi ve strength tests were scheduled for 7; 28,
and 56 days. Strength results were poor, and subsequent testing of the
aggregates for Los Angel es abrasi on wear and sodi um sulfate soundness loss,
yielded values unacceptable for RCC. The high percentages of weak particles
and micaceous mineral s in the weathered rock was probably responsible for the
poor results. The glacial till deposits from the upper reservoir area consist
of more durable transported sands and gravel s. However, insufficient sample
volume was obtained from TLP-2 to allow for aggregate testing in the
1 aboratory.

Materi al from TLP-8 was assi gned a borderl i ne cl assifi cati on of si 1 t to 1 ean
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cl ay (Ml-CLl, wi th a coeffi ci ent of permeabil ity of 2 x 10 cm/sec. The
material could be utilized for an impervious zone, but available quantities
are questionable.

Further detail s on 1 aboratory test results for soil sampl es from Twi n Lakes
Oam and Reservoir are included in Appendix C.

2.3 Slope Stability of Existing Dam

2.3.1 Procedure

Static stabil i ty analyses of the exi sti ng embankment were performed usi ng the
Modified Bishop limit equilibrium procedure. Two different embankment loading
conditions were analyzed. These loading conditions were:

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