Figure 5.--Location of borrow areas and haul roads. (Sheet 2 of 3.) нол 99,000 Continued on sheet 3 CREEK The quantities of impervious materials used in the dam and dike are shown on figure 5. To begin with, a shrinkage factor of 15 percent was used for the zone 1 materials. Examination of construction quantities shows the final shrinkage factor to be about 22 percent. 20. Borrowed Pervious Materials. As with the impervious materials, it was necessary to obtain much of the pervious, zone 2 materials from borrow areas. Zone 2 materials for the dam and dike were obtained from areas G-2, A-1 and B-1 and from selected parts of the required excavation, although only areas G-1 and G-2 were specified as sources of pervious borrow. In area G-2, the ground-water surface varied from 5 to 9 feet below the surface. Information from hand-auger holes, drilled on 200-foot centers or closer, revealed that the upper 12 feet contained sizable pockets of black organic material, swamp muck, and top soil with alfalfa roots interspersed throughout the upper 5 to 8 feet. Below this stratum, 24 to 48 feet below ground surface, free draining sand was plentiful although plus No. 4 sizes were scarce. Because the G-2 area would have been costly and difficult to work and may not have yielded proper gradation of pervious materials, preconstruction zoning studies indicated that zone 2 material should be obtained from area G-2 extended, from area B-1 after the zone 1 material had been excavated from the B-1 area, and from selected parts of the required excavation. It was found during construction that insufficient freedraining material was available from required excavation and that area G-2 would not produce enough material. Accordingly, area A-1 was developed to augment the supply. Area A-1 was selected because the sand was better graded and cleaner than other material available. Laboratory tests on composite samples of pervious materials from G-2 area are shown in figure 6. The same properties were assumed to apply to the materials from G-2 area extended, and to B-1 and A-1 pervious materials. 21. Materials from Required Excavation. It had been expected, and sampling and testing bore out the assumption, that required excavation would yield suitable types of materials for construction of the dam and dike and that these materials could be segregated easily. However, it developed that because of the diversity of the materials . they could not be segregated easily, and large quantities had to be wasted. The quantities used in the dam or wasted and the quantities excavated are shown in Table 1. Quantities are in cubic yards. The waste was not a total loss because the waste areas contributed to structural stability of the dam and prevented seepage from the reservoir. Several types of materials were removed as spillway excavation. The upper spillway area (approach, crest, and upper chute sections) was covered by loess. The lower spillway area (lower chute, stilling basin, and outlet channel sections) consisted of slopewash or talus above the chute and basin areas, and alluvium of sands, silts, and organic material in the outlet channel area. The thickness of alluvium and loess ranged from 0 to about 40 feet. The loess and talus in places was silty, friable to soft, dry to wet, and yellow to brown in color. The Ogallala formation underneath the overburden ranged from clean unconsolidated gravelly sands through compact fine sands and silts to cemented sands and silts. Preliminary exploration tests results from the spillway area impervious remolded materials were as shown in Table 2. Additional explorations of the spillway basin area performed during construction to determine the bearing properties of the Ogallala formation furnished density, moisture content, and permeability data. For nine samples of the finer, relatively impervious, uncemented Ogallala materials, in-place density ranged from 82.7 to 107.9 pounds per cubic foot, and natural moisture contents from 5. 1 to 38.0 percent. For five samples of the coarse, pervious, uncemented materials, in-place density ranged from 101.9 to 139.6 pounds per cubic foot, and natural moisture contents from 5.0 to 19.4 percent. Results of well permeameter tests indicated a permeability ranging from 35.6 to 185,000 feet per year in the spillway area. These diverse soils yielded zone 1, zone 2, and zone 3 materials as shown in the tabulation of required excavation. Twenty-three one-dimensional consolidation tests on undisturbed samples were made to determine compressibility of silty and clayey soil underlying the outlet works. Medium to high compressibility was indicated by these tests. Required excavation from the outlet works also produced zone 1, zone 2, and zone 3 materials similar in character to spillway materials. |