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<br />." .'~d6~.A,g ~ <br />;ttb!~ - <br /> <br />" <br /> <br />found on the left or north abutment. separated only by a shallow gully, and two . <br />additional areas were located on the south abutment. The latter areas, called the <br />South borrow area, consisted generally of poorly graded, medillm sand and sand with <br />excess silt overlapped, in some cases, by silt. In portio os of the South borrow area <br />lenses of cemented Ogallala sand occurred at relatively shallow depths. <br /> <br />The silt generally showed a maximum laboratory density of 107 pounds per <br />cubic foot at 17 percent moisture content. The fine sand with excess silt compacted to <br />a maximum laboratory density of about 118 pounds per cubic foot at 10 to 12 percent <br />moi.sture. Percolation rates varied from 0.02 to 3.06 feet per year for the two types of <br />materials. The poorly graded fine sand generally underlying the SF-silty material was <br />too pervious to be considered for the zone t embankment and limited the cut in most <br />portions of the area. Some of this sand was considered usable [or zone 2 to supplement <br />the sand and gravel from the cutoff trench. <br /> <br />Materiat in the deposits near the left abutment, called the North borrow area, <br />was a very uniform silt occurring to depths of 60 feet, with an average thickness of <br />about 32 feet. The area was capable of supplying impervious material for the entire <br />dam, but because of excessive haul distance for some of the material it was not planned <br />to exploit the area to the fullest extent. Percolation rates were less than O. 10 foot per <br />year. A few in-place density tests indicated that a shrinkage factor of 30 percent could <br />be expected for the impervious material. <br /> <br />The zone 2 material obtained from required structure excavation and portions <br />of the South borrow area was a poorly graded medium sand containing 3 to 8 percent of <br />plus No.4 sieve sizes. <br /> <br />The embankment slopes were influenced largely by the properties of the silty <br />material found in the North and South borrow areas. This material possessed adequate <br />density, shear strength, a.nd load consolidation characteristics. The embankment <br />slopes were varied so as to obtain approximately the same stability at all elevations. <br />This design permitted the maximum and most effective use of the materials locally <br />available. <br /> <br />14. free-Draining Materials and Riprap. - During the reconnaissance period of <br />the investigations, it was proposed that riverbed alluvium could be used Cor free-drain- <br />ing embankment material. Opalized sandstone lenses 1 to 2 feet in thickness, occurring <br />in the Ogallala outcrops in the vicinity of the dam, were also suggested for use as free- <br />draining material. These sources were rejected, however, and free-draining material <br />was obtained from Golden, Colo., for use as a blanket under the riprap. <br /> <br />It was recognized that adequa.te quantities of satisfactory riprap materials <br />probably could not be located in close proximity to the dam site. Suggested sources of <br />riprap were dolomitic limestone from Guernsey, Wyo., basalt or granite from near <br />Golden, Colo. I and deposits of quartzite and opaline sandstone from various locations in <br />Kansas. All of these sources involved rail hauls up to 270 miles, in addition to a 20- to <br />30-mile truck haul from the t'ailhead to the dam site. <br /> <br />.. <br /> <br />Because of the excessive hauls to obtain rock from the above sources, all <br />known rock deposits in the plains region within a radius of 100 miles from the' 'dam, and <br />numerous deposits on the eastern slope of the Rocky Mountains, were investigated. De- <br />tailed investigations by drilling, blast testing, and geophysical methods were made on <br />deposits of sandstone at Herndon and Ludell, Kan., and at Akron, Colo. The thin- <br />bedded nature of these deposits, excessive amount of overburden, low specific gravity, <br />and generally poor quality of the rock led to the conclusion tha.t adequate protection of <br />the dam with this rock would not result in sufficient savings to warrant its use in pref- <br />erence to the basalt or granite available near Golden, Colo. In order to insure obtaining <br />good quality rock for riprap it was decided to specify types having a specific gravity of <br />at least 2.60. Golden was selected as the source of all riprap. <br /> <br />15. Concrete AllllrelZates. - Investigations disclosed that river sand from near the <br />axis of the dam was suitable for fine aggregate provided low-alkali cement was used. <br /> <br />13 <br />