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Seepage Theory – Continuity Equation

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Seepage Theory – Continuity Equation

dx

d  

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Graphical Picture of Two Equations

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Graphical Picture of Two Equations

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Similarly, the head difference between any two

adjacent equipotentials is constant.

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Graphical Picture of Two Equations

Comparing the twoequations, equipotentials

must be perpendicular to

ow nes

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Properties of Flow Nets

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Properties of Flow Nets

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Flow Net Construction

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Flow Net Construction

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Example 1 – Sheetpile Wall

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Example 1 – Sheetpile Wall

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= 8m= 7m

Example 1 – Sheetpile Wall

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Example 1 – Sheetpile Wall

= 16.7 m

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HQ = 17.5 – 8.4*0.455

= 13.7 m

EX 1 – Plaxis Result

H=17.5m H=12.5m

Hp=16.8m Hq=13.6m

16Closed flow boundaries

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EX 1 Plaxis Results

Total discharge = 15.7e-6 m3/s per m

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EX 1 Plaxis Results

Pp=88 kPaPq=66 kPa

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Example 2 – Gravity Dam

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Example 2 – Gravity Dam

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Example 2 – Gravity Dam

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EX 2 Plaxis Results

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EX 2 Plaxis Results

Discharge = 1.63e-4 m3/s per m

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EX 2 Plaxis Results

90 kPa

33 kPa

Uplift pressures

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Dams and Embankments

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Dam Seepage Entry and Exit BoundaryConditions

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EX 3 Dam Seepage

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EX 3 Plaxis Results

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Vertical flow in Stratified Soils

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Ex 4 Flow in Stratified Soils

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Flow Net in Anisotropic Soil

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Flow Net in Anisotropic Soil

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Piping Instability of Sheetpile Wall

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Piping Instability of Sheetpile Wall

=im   w

ci  

   '

Seepage force = i.γw. volume

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Seepage and Effective Stress

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Seepage and Effective Stress

Seepage force in soils is:

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volumeivolume jFs w...     

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Quick condition and critical gradient

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wsat            'Buoyant unit weight =

Quick condition and critical gradient

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EX 4 Effective Stress and Seepage

Determine effective stresses at A and B

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2

51

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