OCR

A number of arrangements and possibilities at this site were studied. Finally, planners decided to form the upper reservoir by blasting off the top of the 900-foot mountain, and to use the rock thus obtained to shape an elliptical dam. The inside face would then be lined with concrete, and the floor paved with asphalt to form a watertight lake capable of holding 1.4 billion gallons of water, with a depth of up to 110 feet. The contract for the hydraulic work was awarded to Fruin-Colnon Contracting Company of St. Louis jointly with Utah Construction and Mining Company of St. Louis jointly with Utah Construction and Mining Company of San Francisco. Missouri Petroleum Products Company, St. Louis, was subcontractor for the asphalt paving. Ground was broken early in 1960. While excavation of nearly three million tons of rock was under way, engineers for Union Electric were conferring closely with engineers and research technologists of The Asphalt Institute to establish the best asphalt paving mix for use in the reservoir floor. Samples of local aggregates and mineral filler arrived at the Institute's College Park, Maryland, laboratories, and after a series of exhaustive tests , a design was formulated. The decision was to use 65% of 3/4-inch traprock, 18% of fine traprock sand, and 17% of limestone sand, bound together with a 60-70 penetration grade asphalt cement. Asphalt content was 7% to 7-1/2% of total weight. Institute technicians calculated that this mix would be waterproof and flexible enough to withstand the traffic of construction equipment during the paving operation. Later the mix design was revised because of a decision to use local trap rock in place of the original gravel, and once more Ashpalt Institute engineers prepared and submitted a new set of specifications, which Union Electric Company accepted for the final mix design. Paving Problems Overcome Work on the asphalt paving began soon after construction of the retaining wall and water tunnel was completed. The paving of 39 acres of an uneven ground proved to be no easy task, and the paver could work at only 35 feet per minute with frequent stops to permit handwork in depres- sions which the screed could not reach. A two-wheel tandem, roller weighing six tons was used for compaction after the contractors rejected a twelve-ton, three-wheel roller as being too heavy. Pneumatic rolling was considered unnecessary, as the required density was reached without it, and a satis- factory surface texture resulted from use of the steel-wheel roller. The asphalt paving was placed on the floor of the reservoir in two layers of more than two inches each, yielding a finished compacted thick- ness of four inches plus. Although there was no requirement that the paving-