DETERMINATION OF PHREATIC LINE WITH OR WITHOUT FILTER FLOW NET APPLICATION OF FLOW NET, The flownet consists of two sets of curvilinear lines known as flow lines equipotential lines., One set of curves (\y-lines) represents the path along which the individual particle of water seep through the soil are called stream lines or flow lines. Flow lines indicate the direction of flow.

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DETERMINATION OF PHREATIC LINE WITH OR WITHOUT FILTER FLOW NET APPLICATION OF FLOW NET:

DETERMINATION OF PHREATIC LINE WITH OR WITHOUT FILTER FLOW NET APPLICATION OF FLOW NET EMBANKMENT DAM

PHREATIC LINE :

PHREATIC LINE Any point p can be located by F as center and QH as radious on PQ vertical line Phreatic line is started from B which is …… Line is always at 90 degree of the u/s face Discharge of dam = q = d2+h2 - d 1/16/2014 2

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1/16/2014 3

Equation of base parabola:

Equation of base parabola (X+s)2 = x2+y2 1/16/2014 4

Darcy’ s law :

Darcy’ s law 1/16/2014 5

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1/16/2014 6

Phreatic line without filter:

Phreatic line without filter 1/16/2014 7

With filter :

With filter 1/16/2014 8

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Figure shows phreatic line emerges at point K in d/s face But base parabola cuts at point J. SO corrections of delta A is required to determined Graphical solution Analytical solution 1/16/2014 9

Graphical solution:

Graphical solution 1/16/2014 10

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1/16/2014 11

Analytical solution:

Analytical solution Schaffernak and Van Iterson for a < 30° 1/16/2014 12

by Casagrande for 30° < a < 60°:

by Casagrande for 30° < a < 60° 1/16/2014 13

Flownet homogeneous dam:

Flownet homogeneous dam 1/16/2014 14

The flownet consists of two sets of curvilinear lines known as flow lines equipotential lines.:

The flownet consists of two sets of curvilinear lines known as flow lines equipotential lines. One set of curves (\y-lines) represents the path along which the individual particle of water seep through the soil are called stream lines or flow lines. Flow lines indicate the direction of flow . 1/16/2014 15

The other set of curves (<f> - lines) represents lines of equal head and called equipotential lines. The head loss caused by water crossing two equipotential lines termed as the potential drop.:

The other set of curves (<f> - lines) represents lines of equal head and called equipotential lines. The head loss caused by water crossing two equipotential lines termed as the potential drop . 1/16/2014 16

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The entire pattern of flow lines and equipotential line is referred to as a flow net. Thus, a flow net is a graphical representation of direction of seepage and head at every point. The space between two adjacent flow lines is called the flow path or flow channel The figure formed on the flownet between any two adjacent flow lines and adjacent equipotential lines is referred to as the field . 1/16/2014 17

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Characteristics of flow net : 1. The flow lines and equipotential lines meet at right angles to one another 2. The fields are approximately squares, so that a circle can be drawn touching all the four sides of the square. 3. The quantity of water flowing through each flow channel is the same. 1/16/2014 18

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4. The potential drop (head drop) between two successive equipotential lines is also s 5. Smaller the dimensions of the field, greater will be the hydraulic gradient velocity of flow through it. 6. In a homogeneous soil, every, transition in the shape of the curves is sr being either elliptical or parabolic in shape. 1/16/2014 19

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applications of flow net are : 1. Determination of seepage 2. Determination of uplift pressure 3. Determination of seepage pressure 4. Determination of exit gradient 1/16/2014 20

Determination of seepage:

Determination of seepage 1/16/2014 21

. Determination of uplift pressure:

. Determination of uplift pressure 1/16/2014 22

Determination of seepage pressure:

Determination of seepage pressure 1/16/2014 23

Determination of exit gradient:

Determination of exit gradient 1/16/2014 24

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