Earthen Dam

a dam built of soil materials (sand, loam, clay, and so on), with a trapezoidal or nearly trapezoidal cross section. Earthen dams are usually of the fixed type (without the flow of water over the crown); they are commonly used in many countries because of their simplicity of construction and maintenance. Six main types of earthen dams are distinguished, depending on the materials used for the body of the dam and the methods of providing waterimpermeability.

Earthen dams may be built on virtually any type of ground base (except strongly liquescent muddy soil). The watertight part of the dam (the baffle and core) is usually joined to the rocky base by a cutoff or a concrete joint tongue, under which a grouted cutoff is set in fissured rock. On a nonrock base, if the water-resistant material (clay or rock) is located at an acceptable depth, the impermeable part of the dam is joined to the water-resistant material by a positive ground cutoff, a sheet pile bulkhead, or a curtain (partial cutoff). A blanket or partial cutoffs and a sheet pile bulkhead, are installed for a deep-lying water support.

Earthen dams are distinguished according to their construction method as fill dams, which are built up by dry pouring of soil, with artificial consolidation and without consolidation (with pouring of the soil into the water or by means of a directed explosion), and hydraulic fill dams, the construction of which (the aggradation of the body of the dam) is accomplished by the hydromechanization method. The drainage of an earthen dam is usually made in the form of a drainage shell or a drainage mattress buried in the body of the dam. Rock fill and paving stone facing covered with concrete or reinforced-concrete slabs are used to protect the upstream (pressure) slopes of earthen dams against wave action. The downstream slopes are protected by planted grass, turf, poured gravel, and crushed stone. Modern mechanical excavation methods make possible the construction of earthen dams to heights of 150 m or more.