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Figure 20.--A 2-1/2-cubic-yard shovel used to work a 30-foot face in borrow area 6.
Material was carried to separation plant by 17-cubic-yard bottom-dump trailers. 5-SL-760, August 2, 1950
Figure 21. --Loading operations in gravel area No. 2. The dragline with 2-cubic-yard
bucket was used to load 11-cubic-yard end-dump trucks. 5-SL-840,
Figure 22. --Embankment placing operations during early stages of construction.
5-SL-686, June 29, 1950
Placing was resumed in June 1950, with the first zone 1 material being tamped in the dike section June 20. Operations were extremely slow during July as the material was at or above optimum moisture content and there were continual rainstorms. Conditions improved, however, and progress was satisfactory until operations were terminated for the season. Satisfactory progress was made throughout the unusually dry season of 1951 and the dam and dike embankments were completed August 25, 1951. Figures 22, 24, and 25 show embankment placing operations.
Placing of the four classes of material used in construction of the dam is discussed in the following sections.
58. Earth Fill (Zone 1). - Material for zone 1 was obtained from two borrow areas, No. 6 and the extension of No. 6 (sec. 28). Excavation of these areas is discussed in section 53. These areas are a morainal deposit, the material consisting largely of gravel with sand-clay binder which proved to be an excellent impervious material. Borrow area 6, the initial source, proved to contain far more moisture than was either evidenced or reported in preconstruction investigations. Moisture in place varied from optimum to, more frequently, 1 or 2 percent above optimum. This moisture condition made placing operations costly. Little drying effect was obtained through air jetting at the separation plant and by other means attempted in the pit. The best method of drying was to scarify and disc-harrow the material on the fill before rolling. Frequent rainstorms forced suspension of operations and heavy dews were sufficient to delay starting in the early morning hours.
On August 25, 1950, permission was granted the contractor to increase the maximum size of rock allowable in zone 1 from 3 to 5 inches and to change the downstream slope of zone 1 in the main dam from 1 to 1 to 1/2 to 1 (sec. 28). Addition of the 5-inch rock lessened the difficulties caused by excessive moisture and reduced somewhat the tendency of the screens in the separation plant to plug. It is interesting to note that this change in slope reduced the cross section of the zone 1 to the least section of any rolled-earth dam yet constructed by the Bureau.
The second borrow area, the extension of area 6, was opened on September 11, 1950, when it was determined that the material, although more thoroughly consolidated and difficult to excavate, was considerably drier.
Material was excavated and loaded in the pit by a power shovel and transported to the separation plant in bottom-dump trailers. After separation, the material was reloaded in bottom-dump trailers and/or end-dump trucks for transporting to the dam and dike. Spreading was accomplished by bulldozers and, depending upon moisture content, the material was either sprinkled or scarified to increase or reduce the moisture content prior to rolling with dual-drum sheepsfoot rollers. Upon being granted permission to include up to 5-inch rock in the impervious section of the dam, the contractor agreed to increase the number of roller passes from 12 to 14 at no additional cost to the Government.
59. Sand and Gravel Fill (Zones 2 and 4). - Materials for use in zone 2 and a major portion of zone 4 were obtained from borrow areas located in the streambed and flood plain upstream from the dam. The material consisted of clean well-graded river sand and gravel having a maximum size of 3 inches. The material was ideal for the purpose intended, being easily placed and well suited to the compaction specified.
The material was placed in approximately 12-inch lifts and was required to be thoroughly wetted prior to compacting with four passes of a heavy crawler tractor (fig. 24).
Field densities of the material indicate that the material was compacted to an average of 80 percent of relative density (sec. 16). Seventy percent had been proposed as adequate.
Placing methods in the zone 4 section were the same as outlined above. The material type just discussed was used, along with suitable dam foundation excavation and oversize screenings from the separation plant, to make up the total yardage requirements.