C150094 Application ‎(2)‎

• Contract/PO #: C150094
• Contractor Name: La Plata Water Conservancy District
• Contract Type: Grant
• County: La Plata
• Loan Projects - Doc Type: Application

penetration tests and rock coring. Test pits will be utilized in borrow areas to obtain bulk
samples.
Three test borings will be drilled along the alignment of the proposed dam. One hole will
be drilled at each abutment to a depth of approximately 150 feet and one hole will be
drilled near the streambed to a depth of approximately 80 feet. These holes will be
drilled to determine the strength,permeability and compressibility of the materials
directly below the proposed embankment. Soil penetration tests will be taken every 5
feet in the overburden soils and the rock beneath the site will be cored continuously to the
maximum hole depth. Packer tests will be conducted at 5 locations in the abutment holes
and 2 locations in the foundation hole to evaluate in situ permeability. A 2-inch plastic
pipe piezometer will be placed in each of the holes. The piezometer will be slotted at
appropriate depths based upon the conditions encountered and a protective cover will be
installed at the ground surface for subsequent water level readings.
Subsurface conditions in the valley bottom within the reservoir will be explored to
evaluate the suitability of this area as a borrow site and the ability of the reservoir to
retain water. Four test borings to a depth of 50 feet and 3 test pits to a depth of
approximately 15 feet are anticipated for this part of the study. Three additional test pits
will be required on the valley sides in the reservoir or above the proposed water surface
elevation to explore for suitable riprap and/or concrete aggregate.
Alternative spillway configurations on the right abutment will be evaluated by drilling
three 50-foot deep test holes to investigate the subsurface profile. Slotted PVC
monitoring wells with protective covers will be installed in the all test holes.
Specifications for subsurface investigations were prepared by and a proposal was
obtained from Western Engineers in Grand Junction to provide the equipment and
materials necessary to conduct the subsurface investigations, including access to the
location of test pits and test borings.
Laboratory Testing Program
A laboratory testing program will be conducted to evaluate the shear strength,
compressibility classification and permeability of the soils and bedrock encountered at
the site. Direct shear strength testing will be conducted for two embankment soil types.
Each shear strength envelope will be developed by conducting three drained direct shear
tests at different normal loads. The testing program will include a set of two time
consolidation tests to evaluate the rate and compressibility of compacted embankment
soils. The testing program will include standard property testing such as Atterburg limits,
gradation analyses,pinhole dispersion tests and compaction curves from which
classification, compressibility and permeability information can be approximated for the
on-site soils.
Durable rocks, including potentially the Cliff House Sandstone, will be evaluated as a
source for riprap and concrete aggregate. The investigation will be limited during this
study to petrographic analyses, Los Angeles abrasion testing, specific gravity and a
review of USBR studies on nearby dam sites.
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