Question

The pressure on a phreatic line is equal to atmospheric pressure???

Answer 1

The top flow line of a saturated soil mass below which seepage takes place, is called the Phreatic line. Hydrostatic pressure acts below the phreatic line whereas atmospheric pressure exists above the phreatic line. This line separates a saturated soil mass from an unsaturated soil mass. It is not an equipotential line, but a flow line.

For an earthen dam, the phreatic line approximately assumes the shape of a parabola.

Answer 2

Yes, the pressure or the hydrostatic pressure on a phreatic line is equal to atmospheric pressure.

Explanation:

• The phreatic line is the top flow line of a saturated soil mass below which seepage takes place.
• It is also called the saturation line or seepage line.
• It is an imaginary line inside the dam section.
• The hydrostatic pressure above this line is negative and the hydrostatic pressure below this line is positive.
• The hydrostatic pressure on the phreatic line represents atmospheric pressure or it is equal to the atmospheric pressure.
• Atmospheric pressure is zero at the phreatic line.
• The position of the phreatic line has an influence on the stability of the dam.
• Above the phreatic line, a capillary zone lies which is also called capillary fringe. Here, the hydrostatic pressure is negative.

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