Explain phreatic line in earthen dam with a sketch.

Explain phreatic line in earthen dam with a sketch.
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Answer :

Phreatic line in earthen dam1.The line in earthen dam section below which there is positive hydrostatic pressure exists. Phreatic line separates the dry and wet part of earthen dam body as it acts as boundry between them, as shown in Fig.No 7

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2. Phreatic line indicates zone of seepage through earth dam at which hydrostatic pressure acting is zero. Below phreatic line, soil is always in fully saturated condition. 3.When phreatic line ends at down-stream side of earthen dam, then there are chances of hydraulic failure of earthen dam in the form of piping. Therefore, a hearting is provided to break the flow zone of phreatic line. 4.When phreatic line ends at toe of earthen dam, then there may be sloughing of toe material. Hence, a rock toe is necessary to avoid removal of toe portion of dam. 

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