In seepage through an earth dam, the 'phreatic line' is:
Choose the correct answer
The axis of the dam
Upper boundary of saturated zone in dam body — its position governs slope stability and seepage quantity
The downstream toe drain location
The clay core centreline
Correct Answer
B. Upper boundary of saturated zone in dam body — its position governs slope stability and seepage quantity
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Phreatic line (seepage line / saturation line): upper boundary of seepage zone within earth dam. Below it: saturated (pressure > atmospheric). Above it: dry (or capillary fringe). Location determines: uplift on downstream slope, exit gradient (piping risk), seepage quantity Q = k×Nf/Nd×H. Casagrande''s method: parabola starting from point on upstream face to a corrected exit point on downstream slope.
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