Page images
PDF
[graphic][ocr errors][ocr errors][ocr errors][merged small][ocr errors]

the spillway excavation was also investigated. The south borrow area consisted of two ridges divided by a dry wash and comprised an area about 3, 500 feet square. The locations of borrow areas are indicated in figure 5.

The north borrow areas were explored with hand auger holes, power drill holes, and test pits. Samples taken from these areas indicated a fairly homogeneous soil which was dominantly silt and some fine sand. Laboratory tests indicated maximum density ranging from 101.7 to 109.8 pounds per cubic foot at optimum moisture contents ranging from 15.5 to 18.7 percent. Permeability tests indicated an average coefficient of 0.1 foot per year. The average for the in-place density tests indicated a shrinkage factor of 23 percent.

The south borrow area was investigated with hand auger holes which in some instances extended to a depth of 70 feet. The soil was classified into three general types: silt with very fine sand; medium to fine sand with excess silt and small amount of clay; and medium to fine, silty to fairly clean sand. The soil was somewhat heterogenous with irregular recurring layers of sand, silt, and sand containing excess silt. A relatively homogeneous material could be obtained by controlling the depth of cuts in the borrow area. Laboratory tests of the silty sand indicated maximum densities ranging from 108 to 122.7 pounds per cubic foot at optimum moisture contents ranging from 8.0 to 13.6 percent. The shrinkage factor was about the same as that of materials in the north borrow areas.

(b) Riprap and Rock-Btonket Moteriats.— Several sources for riprap and rock-blanket materials were considered. The three most feasible sources were: Franklin, Nebr., for quartzitic sandstone; Golden, Colo., for basalt or granite; and Guernsey, Wyo., for dolomite. A study of the freight rates, quality, quantity, and production costs indicated that the hard, sound, and durable metamorphosed granite with a specific gravity averaging about 2.7 obtained from a quarry at Golden, Colo, would be the most suitable for the riprap and rock-blanket of the dam. Rock obtained from the Golden quarry required blasting and processing at the quarry, shipment by railroad to Trenton, Nebr., and hauling by truck for a distance of 2-1/2 miles to the dam.

8. Railroad, Highway, and County Road Relocation Studies. - (a) Roitroad.— Relocation studies for the Chicago, Burlington and Quincy Railroad were started in 1947. These investigations included several routes having a combined length of 62 miles. The railroad company provided data and assisted in the selection of the route. Some of the studies for the relocation work included:

(1) Cost estimates for raising the railroad grade to the crest elevation of the dam.

(2) Widening cut sections for additional borrow materials.

(3) Stability of embankment.

(4) Increased earthwork because of flattening fill slopes.

(5) Costs of road crossings, cattle passes, etc., versus combined structures for passes and drainage.

(6) Costs of road crossings and cattle passes versus severance costs for rightof-way.

(7) Switching details for the Trenton switchyard.

Preliminary data, which included alinement and profile, structure topography, section corner ties, right-of-way requirements and quantity estimates were completed during April 1949. The railroad company approved the relocated line in October 1949. Final plans and specifications were submitted to the railroad company in April 1950 and approved during June 1950. The selected route is shown on figure 6.

(b) Htghuoy.-- Studies for a relocation of U.S. Highway No. 34 were begun in April 1948. Several routes were studied and cost estimates were made of each to

[graphic][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors][ocr errors]
[graphic]

determine the most economical route. A route through Trenton, Nebr., was favored by the Bureau of Reclamation. Subsequently, the Bureau of Public Roads in conjunction with the State of Nebraska, recommended a route north of the relocated railroad and additional studies were made of the "all northside" route (fig. 6). This route eliminated two underpass structures, some objectionable grades, and the traffic hazard of passing the highway through the city limits of Trenton. Also, the State of Nebraska designed the relocated highway in conformance with modern standards at a cost exceeding that of a replacement in kind. All of these additional costs were to be borne by the State. An inventory, including photographs of the existing highway, was made for record purposes and to aid in negotiations .

The Bureau's estimates were based on an estimated grade placed on a centerline profile. Structure locations were selected. Waterway openings were computed from drainage areas using the Talbot formula with C = 0.9. Lengths of culverts were estimated by using standard fill sections at structure sites, and bridge lengths were estimated from profiles. Unit costs were then applied to excavation, structures, and other items.

(c) County Rood.— Nine miles of county road south of Swanson Reservoir were relocated. This relocation work involved the preparation of design data, including preliminary alinement and profile cross sections, and drainage areas.

« PreviousContinue »