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Prof Harry Tan CE5101 Seepage SEP 2011
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CE5101 Lecture 3
Seepage through Soilsby
Prof Harry Tan
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SEP 2011
Outline
Seepage TheoryP t ti l d St F ti Potential and Stream
Functions
Flow Nets and FEM models Seepage through Dams and
Embankments Seepage in Anisotropic Soils
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Seepage in Anisotropic Soils Instability due to Seepage Seepage
and Effective Stress
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Prof Harry Tan CE5101 Seepage SEP 2011
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Seepage Theory Continuity Equation
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Seepage Theory Continuity Equation
dxd
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Prof Harry Tan CE5101 Seepage SEP 2011
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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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Prof Harry Tan CE5101 Seepage SEP 2011
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Graphical Picture of Two Equations
Comparing the two equations, equipotentials must be
perpendicular to fl liflow lines
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Properties of Flow Nets
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Prof Harry Tan CE5101 Seepage SEP 2011
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Properties of Flow Nets
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Flow Net Construction
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Prof Harry Tan CE5101 Seepage SEP 2011
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Flow Net Construction
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Example 1 Sheetpile Wall
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Prof Harry Tan CE5101 Seepage SEP 2011
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Example 1 Sheetpile Wall
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= 8m= 7m
Example 1 Sheetpile Wall
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Prof Harry Tan CE5101 Seepage SEP 2011
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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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Prof Harry Tan CE5101 Seepage SEP 2011
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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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Prof Harry Tan CE5101 Seepage SEP 2011
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Example 2 Gravity Dam
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Example 2 Gravity Dam
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Prof Harry Tan CE5101 Seepage SEP 2011
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Example 2 Gravity Dam
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EX 2 Plaxis Results
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Prof Harry Tan CE5101 Seepage SEP 2011
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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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Prof Harry Tan CE5101 Seepage SEP 2011
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Dams and Embankments
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Dam Seepage Entry and Exit Boundary Conditions
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Prof Harry Tan CE5101 Seepage SEP 2011
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EX 3 Dam Seepage
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Prof Harry Tan CE5101 Seepage SEP 2011
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EX 3 Dam Seepage
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EX 3 Plaxis Results
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Prof Harry Tan CE5101 Seepage SEP 2011
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EX 3 Plaxis Results
Discharge = 17.1e-6 m3/s per m
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Horizontal flow in Stratified Soils
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Prof Harry Tan CE5101 Seepage SEP 2011
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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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Prof Harry Tan CE5101 Seepage SEP 2011
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Flow across Soil Interface
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Piping Instability of Sheetpile Wall
D=d (same item)
dhi mavg
Datum
hm
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Prof Harry Tan CE5101 Seepage SEP 2011
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Piping Instability of Sheetpile Wall
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Piping Instability of Sheetpile Wall
=im wci
'BUT Seepage force = i.w. volume
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Critical gradient divide by Applied gradient
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Prof Harry Tan CE5101 Seepage SEP 2011
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Measures against Piping
Fill w
d'
wmh d'
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Seepage and Effective Stress
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Darcys law is v=ki (average seepage velocity or Darcy velocity
or apparent or superficial velocity)
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Prof Harry Tan CE5101 Seepage SEP 2011
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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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volumeivolumejFs w... ie Seepage Force = Seepage Pressure x
Volume
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Prof Harry Tan CE5101 Seepage SEP 2011
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Quick condition and critical gradient
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wsat 'Since buoyant unit weight =
Quick condition and critical gradient
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Prof Harry Tan CE5101 Seepage SEP 2011
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EX 4 Effective Stress and Seepage
Determine effective stresses at A and B
hs=
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(Total stress at A)
(Pore water pressures at A)
(Effective stress at A)
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Seepage pressures at A= wi .
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Prof Harry Tan CE5101 Seepage SEP 2011
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wsA ih .'' i.e.A'
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