Hydraulic-fill Dams.
No discussion of earth dams would be complete without some reference being made to the novel type of construction developed in western America in recent years, by which railroad embankments and water-tight dams are built up by the sole agency of water. The water for this purpose is usually delivered under high pressure, as it is generally convenient to make it first perform the work of loosening the earth and rock in the borrow pit, as well as subsequently to transport them to the embankment, and there to sort and deposit them and finally part company with them after compacting them solidly in place, even more firmly than if compressed by heavy rollers. Sometimes, however, water is delivered to the borrow pit without pressure, in which event the materials must be loosened by the plow or by pick and shovel by the process called ground sluicing in placer mining parlance.
An abundance of water delivered by gravity under high pressure is usually regarded as one of the essential factors in hydraulic-fill dam building, but it is not essential that there be a large continuous flow. The Lake Frances Dam, recently constructed for the Bay Counties Co., of California, by J. D. Schuyler, is 75 ft. high, 1,340 ft. long on top, and contains 280,000 cu. yds. The dam was built up by materials sluiced by water that was forced by a centrifugal pump through a 12-in. pipe and 3-in. nozzle, against a high bank, whence the materials were torn and conveyed by the water through flumes and pipes to the dam. About 6 cu. ft. per sec. of water was thus used, and at one stage of the work the supply stream was reduced to less than 0.1 ft. per sec., the water being gathered in a pond and pumped over and over again.
The chapter on hydraulic-fill dams in Mr. Schuyler’s book on “Reservoirs for Irrigation” will be found to contain matter on the subject interesting to those who desire to pursue it further, and the reader is again referred to that work.