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<br />consisted of a thin veneer of natural topsoil overlying natural clays andlor sands and clays, and claystone bedrock to
<br />the maximum depth investigated, 25 feet. The subsurface conditions encountered in the existing embankment and
<br />proposed borrow areas are described in more detail in the following sections.
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<br />Existing Embankment: Man-made fill materials were encountered at the ground surface in the test holes drilled in
<br />the upstream face of the existing embankment. The fill materials generally consisted of clays, which were sandy to
<br />very sandy, low to moderately plastic, soft to stiff, moist to wet and light brown to reddish brown in color, The
<br />upper 4 to 12 feet of fill materials encountered in the test holes appeared to be softer and exhibit a higher moisture
<br />content than the fill materials encountered deeper in the test holes, The clay fill materials typically classified as CL
<br />soils in accordance with the Unified Soil Classification System, Results of the unconfined compressive strength
<br />tests run on samples of the clay fill materials, indicate that these materials will exhibit unconfined compressive
<br />strength values ranging from 1,200 to 4,100 psf in their present state, However, when remolded to approximately
<br />95% of the maximum standard Proctor density and near the optimum moisture content, an unconfined compressive
<br />strength of9,000 psfwas obtained on these materials,
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<br />A layer of natural topsoil materials was encountered beneath the clay fill materials in each of the test holes drilled in
<br />the embankment. The topsoil layer ranged from I Y, to 2 Y, feet in thickness. Natural clays were encountered below
<br />the topsoil materials, The clay layer ranged from 4 to 8 feet in thickness, The natural clays were slightly sandy to
<br />very sandy with occasional gravels, low to moderately plastic, stiff to very stiff, moist to very moist and reddish
<br />brown to dark brown in color, The clays classified as CL soils in accordance with the Unified Soil Classification
<br />System, The results of the unconfined compressive strength test run on a sample of the relatively undisturbed
<br />sample of the clays, indicates that this sample exhibited an unconfined compressive strength value of 5,500 psf,
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<br />Claystone bedrock of the Wasatch Formation was encountered below the natural clays and extended to the
<br />maximum depth investigated, 41 feet. The claystone bedrock was nil to slightly sandy, moderately plastic, medium
<br />hard to hard, moist and brown to gray in color, A sample of the claystone bedrock classified as a CL soil in
<br />accordance with the Unified Soil Classification System, The results of the unconfined compressive strength test run
<br />on a relatively undisturbed sample of the claystone bedrock, indicates that the sample tested exhibited an unconfined
<br />compressive strength value of 12, I 00 psf,
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<br />Groundwater seepage was encountered in all three of the test holes drilled in the embankment. The groundwater
<br />levels, shortly after the drilling was completed. appeared to be located just below or in the layer of natural topsoil
<br />materials, However, when measured 293 days after the drilling was completed, the groundwater levels were
<br />encountered from 0 to 2 feet above the topsoil layer. It should be noted that no apparent movement had occurred in
<br />the embankment soils in the vicinity of the temporary casings when the measurements were taken 293 days after the
<br />drilling was completed, The depths/elevations at which the groundwater levels were encountered, as well as the
<br />number of days after the measurements were taken are shown in the Logs of the Exploratory Test Holes in Figure
<br />#3,
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<br />Borrow Area: Two different borrow areas were evaluated during this investigation, The first borrow area is situated
<br />to the east-southeast of the existing spillway and along the south shore of the reservoir, Two test holes were drilled
<br />in this area to investigate the overburden soils and bedrock conditions, The second borrow area is situated at the
<br />east end of the reservoir, Four test pits were advanced in this area to evaluate the depth, quality and moisture
<br />condition of the proposed borrow materials, The subsurface conditions encountered in both of the borrow areas
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<br />Job Number: 00-4660
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<br />NWCC. Inc,
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