Embankment Dams

A broad spectrum of natural and fabricated materials have been used in the construction of embankment dams. Embankment dams are made by building an embankment of gravel, sand, and clay across a river. To prevent leakage, often a core, or inner wall, of concrete or other watertight materials is used. In a rolled-fill dam, earth is hauled by vehicles onto the dam and rolled tight with heavy machinery. In the hydraulic fill dam, earth is carried to the dam by water in pipes or flumes and also deposited by the water. The placing of the earth is so controlled that the finer, watertight materials form the core. In the semihydraulic fill dam, trucks bring the earth to the dam and jets of water distribute the materials. Rock dams are made by dumping rocks across the river. A wall of rocks is then laid on the upstream side and over this is built a waterproof facing of reinforced concrete, timber, or steel.

Controlling factors in choosing this type of dam are the amounts and types of materials locally available for construction and the size and configuration of the dam. Many small embankment dams are built entirely of a single type of material such as stream alluvium, weathered bedrock, or glacial till. Larger embankment dams generally are zoned and constructed of a variety of materials, either extracted from different local sources, or prepared by mechanical or hydraulic separation of a source material into fractions with different properties. Where rock is used extensively, it may be obtained by separation from bowldery stream deposits, glacial till, side-rock accumulations, or by quarrying.

Construction of an embankment dam requires prior investigation of foundation geology and an inventory and soil-mechanics study of materials available for emplacement in the embankment. An important element in a zoned dam is an impermeable blanket or core which usually consists of clayey materials, obtained locally. In the absence of such materials, the dam is built of quarried rock or unsorted pebbly or bowldery deposits, and the impermeable core is constructed of ordinary concrete or asphaltic concrete. Alternatively, in locations where natural impermeable materials are unavailable, embankment dams are built of rock or earth-rock aggregates and impermeable layers

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Figure 1.1: Idealized section of embankment dams a) Rock-fill dam with symmetrical clay core b) Rock and gravel dam with reinforced concrete slab

Figure 1.1: Idealized section of embankment dams a) Rock-fill dam with symmetrical clay core b) Rock and gravel dam with reinforced concrete slab of reinforced concrete, asphaltic concrete, or riveted sheet steel are placed on the upstream face of the dam. Control of seepage through the dam or under it commonly requires installation of porous materials within or immediately beneath the dam.

Embankment dams have been built on a great variety of foundations, ranging from weak, unconsolidated stream or glacial deposits to high-strength sedimentary rocks and crystalline igneous and metamorphic rocks. A particular advantage of an embankment dam, as compared with a concrete dam, is that the bearing-strength requirements of the foundation are much less. Minor settlement of an embankment dam owing to load stresses during and after construction generally is not a serious matter because of the ability of the embankment to adjust to small dislocations without failure. Cross-sections of selected examples of embankment dams are shown in figure 1.1.

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