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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The project area Is located in Zona 1 of the Seismic Zone Map of the United States in the
1988 publication "Advanced Dam Engineering." Zone 1 Is defined as an area which may
experience minor earthquake damage and has an assigned seismic coefficient of 0.05. For
seismic stability analysis, a peak horizontal acceleration of 0.10 was chosen to allow for
uncertainties.

5.3.2 INVESTIGATIONS

5.3.2.1 Field Investigations

Field Investigations for the feaslbiltty study were conducted by WCC between October 23
and 25, 1989. This work involved drilling fIVe test holes from the crest of the embankment.
Piezometers were Installed the five test holes. The location of these test holes Is shown on
Figure 1, and summary logs are shown on Figure 2.

WCC also conducted field investigations for the reconstruction of the dam In 1965. This
work involved drilling 9 test holes near the embankment and excavating 12 test pits in the
reservoir area. The approximate location of these test holes and test pits are also shown
on Figure 1. Summary logs of these test holes are shown on Figure 3 and summary logs
of the test pits are shown on Figure 4.

WCC supervised the drilling and sampling operations. The test holes were drilled by Drilling
Engineers, Inc. under subcontract 10 wee. The test holes were drilled using 3.75-inch I.D.
hollow stem augers powered by a truck-mounted CME-55 drill rig. In all fIVe test holes, a
field-slotted, glued-Joint PVC stand pipe was inserted into the hollow stem auger. The
annulus between the stand pipe and the test hole wall was filled wtth silica filter sand as
the hollow stem augers were removed.

Test holes were generally sampled at 5-foot Intervals. Samples were obtained using either
a two-inch 0.0. standard spltt-spoon sampler or a two-inch I.D. Cal~ornia sampler driven by
a 14O-pound hammer failing 30 inches. The penetration resistance of the sampler (blow
count) was recorded in blows per 12 inches or less. Cal~ornia samples were retained in
2-inch diameter by 4-lnch long brass lubes sealed with plastic caps after removal from the
sampler. When recovery problems were encountered wtth the Cal~ornia sampler, the split-
spoon sampler was used. Split-spoon samples were saved by placing them in brass tubes

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