Seepage and flow nets

A flow net is a graphical representation of the pattern of the seepage or flow of water through a permeable soil. It is possible, by means of a flow net, to calculate the hydrostatic uplift on a structure such as a dam or barrage, the amount of seepage

Water surface

Flow lines

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y Sheet pile wall A /Side b F°"idation pit

Equipotential lines y Sheet pile wall A /Side b F°"idation pit

Level of toe of sheet piling

Level of toe of sheet piling

Impervious stratum, e.g. clay

Concrete. Water surface dam

Flow lines Equipotential lines

Concrete. Water surface dam

Flow lines Equipotential

Homogeneous soil

Impervious stratum

Rolled fill dam of fine, clean sand Water surface ^-

Impervious stratum

Figure 9.31 Examples of flow nets for simple cases, (a) Beneath sheet pile wall; (b) beneath concrete dam on sand with sheet pile cutoff wall; (c) through rolled fill dam with toe drain through an earth dam or under a barrage, or estimate the probability of piping occurring in a cofferdam, for example.

A flow line is the path followed by a particle of water flowing through a soil mass. Flow lines are always smooth, even, curves as shown in Figure 9.31. An equipotential line is a line joining points at which the hydraulic head is equal; therefore, if standpipes are inserted into any two points on an equipotential line, the water will rise to the same level in each standpipe. Flow lines and equipotential lines are always at right angles to each other. For a discussion on the theory of flow nets, see Ceder-gren.58

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Responses

• tori
What is seepage line theory?
3 years ago
• mohamed
What are the design methods of seepage theories?
3 years ago