Performance Evaluation of Internal Drains of Earthen Dams

Seepage is always expected in earthen dams because they are made of porous materials. However, it should be always under control and its amount and pore-water pressures should be kept below acceptable limits. This can be satisfied by installing internal drains. This study reviews the characteristics of blanket, chimney, and toe drains and assesses their suitability and effectiveness for various material types and geometric characteristics in separate cases. Numerical simulations are conducted for steady-state seepage through a homogeneous and simple zoned earthen dam using the finite-element method. It is found that the seepage rate increases and the phreatic line shortens with an increase in the blanket drain length; the phreatic line becomes steeper within the core if the chimney drain material is relatively coarse; and the seepage rate becomes higher when the height of the toe drain is increased. The thickness of the blanket drain and the material gradation of the toe drain are found ineffective in the seepage behavior of the dams considered. (C) 2018 American Society of Civil Engineers.