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e-ISSN: 2581-9763
Volume-6, Issue-2 (May-August, 2021)
Journal of
Geotechnical Studies
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Seepage Characteristics of Homogeneous and Non-homogeneous Earthen
Dam by FEM
Shah Alam1, Miraz Ahamed2*, Mahmud Hasan3
1Jr. Structural Engineer, Design Alliance Ltd., Dhaka, Bangladesh
2,3Lecturer, Department of Civil Engineering, Rajshahi University of Engineering & Technology,
Dhaka, Bangladesh
*Corresponding Author: maruet004@gmail.com
ABSTRACT
From the safety point of view the
consideration of seepage through the earthen
dam is very important factor in geotechnical
engineering. There are many important terms
and many important things related to this
structure. The sluggish pass of water through
small porous materials is seepage. On the
other hand, failure of dams occurs when the
passing rate of seepage is out of control. The
main target of this paper is to show the
comparison of seepage flow through
homogeneous and non-homogeneous earthen
dam by Finite Element Method (FEM). For
this analysis, a sub program of Geo studio,
SEEP/W [12], has been applied. All the
program is performed both for the
homogeneous and non-homogeneous earthen
dam. For this purpose, some other materials
are also used such as silty clay, clay with
blanket filter, horizontal filter, toe combined
with horizontal drains, rock toe, internal clay,
transition filter. After completing this
analysis, it is possible to measure the amount
of water passing through the seepage for both
conditions in pervious and impervious at the
homogenous and non-homogeneous earthen
dam. It is clearly observed that there is a
difference between homogeneous and non-
homogeneous earth dams.
Keywords-- Blanket filter, Earthen dam, FEM,
Horizontal filter, Internal clay core, Transitional
filter, Rock toe
INTRODUCTION
The dam is such a type of hydraulic
structure that is built crosswise to the flow of
water to store water. At the time of drought, this
store water is so much important for agricultural
land for producing crops. The dam is also used
to protect the valuable structure, materials,
humans, and animals from the adverse effect of
inundation. So, Dam failure is one of the most
important topics nowadays. Dam failure is not a
new incident. All of the countries in the world
more or less face such a destructive failure.
When extremely permeable holes are created
into a dam, seeping of liquid may begin at an
extensive rate. This failure occurs in both
homogeneous and non-homogeneous dams.
Currently, Sazzad and Islam analyzed different
types of seepage control measures of earth dam
by FEM for a homogeneous earth dam. In this
paper, a comparison between the homogeneous
and non-homogeneous seepage control measures
is studied. The main intentions of this paper are:
1. To discuss the various characteristics of a
homogeneous and non-homogeneous earth
dam.
2. To find out variations of pore-water
pressure, velocity, and gradient with respect
to distance.
3. To apply various filter media (i.e.
horizontal filter, blanket filter, a transition
filter, rock toe, etc.).
4. To check the variations by changing
materials properties.
5. To take the necessary steps to control the
dam failure by seepage.
METHODOLOGY
Numerical model
In this analysis, SEEP/W (12), a sub
program of geo studio, was applied for
numerical modeling and the finite Element
Method (FEM) is used in essential cases. In this
analysis, many filter media is also utilized. In
this paper, the size of the dam [1-4 and 6-7] was
taken as the same in elevation (m) and length
(m). In 5 no. dam, its elevation (m) is larger than
the others dam but length (m) is the same. The
15
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e-ISSN: 2581-9763
Volume-6, Issue-2 (May-August, 2021)
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inclination angle of the dam face is 30.96° with
the axis of horizontal: vertical = 10:6 for both
faces of upstream and downstream. For
analyzing this, there did not vary the angle (i.e.
angle of the slope are keeping similar). Silty clay
is used in all the dams. But in the foundation of
the dam, there were alternately used silty clay
and clay. In Fig. 1, there was no filter. In Fig. 2,
there was a horizontal blanket filter. In this
horizontal blanket filter, fine sand is applied in
the upper layer and coarse sand is applied at the
lower layer. In Fig. 3, a horizontal filter is
applied. In Fig. 4, there was used a rock toe
combined with horizontals drains. In Fig. 5,
there were used four types of materials in four-
layer at the downstream side. In Fig. 6, there
were used different types of shapes of clay core
(such as rectangular, parallelogram, inclined). In
dam 7, there was used a transitional filter. To
determine the seep variation of the
characteristics of homogeneous and non-
homogeneous earth dam, the flow of water was
kept constant and this constant water level was
above 5m from the base of the dam.
Material properties
At the downstream side of the dam
body, the potential seepage face is considered.
For avoiding difficulties only saturated condition
is taken into account. Other conditions are not
taken into consideration. Different types of
materials which are applied in the dam are given
the Table 1 and the coefficient of permeability of
this material is shown in Table 2.
Table 1: Different types of materials used in the dam.
Elements name
Figure no.
Materials name
Dam body
1 to 7
Silty clay
Foundation of dam
1 to 7
Alternately silty clay and clay
Horizontal blanket filter
2
Fine sand and coarse sand separately
Horizontal filter
3
Coarse sand
Rock toe combined with
horizontal drains
4
Coarse sand
Rock toe
5
Fine sand, coarse sand, gravel and impervious rock
Internal clay core
6
clay
Transition filter
7
Coarse sand
Table 2: Coefficient of permeability of various materials used in the analysis.
Materials
Coefficient of permeability, k (m/sec)
Silty clay
clay
Fine sand
Coarse sand
Gravel
Impervious Rock
Figure 1: Geometric model of an earth dam.
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Figure 2: Geometric model of earth dam with horizontal blanket filter.
Figure 3: Geometric model of earth dam with horizontal filter.
Figure 4: Geometric model of earth dam with rock toe combined with horizontal drains.
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(a)
(b)
Figure 5: Geometric model of earth dam with an arrangement of rock toe: (a) vertical layer; (b)
inclined layer (with an angle of 60
).
(a)
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(b)
(c)
(d)
Figure 6: Geometric model of earth dam with an arrangement of internal clay core: (a) rectangular
clay core; (b) trapezoidal clay core: (c) parallelogram shaped clay core (angle of inclination arm
140
); (d) parallelogram shaped clay core (angle of inclination arm = 40
).
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(a)
(b)
Figure 7: Geometric model of earth dam with an arrangement of transition filter: (a) full transition
filter over the clay core; (b) partial transition filter over the clay core.
RESULTS AND DISCUSSIONS
Earth dam without any filter media
An earthen dam is shown in Fig. 1
where the dam body consists of a single
material. For homogeneous earthen dam, silty
clay is used both in the earthen dam and in the
foundation, and for the non-homogeneous
earthen dam is contained silty clay but the
foundation is contained clay. From this, when
considering homogeneous conditions, pore-
water pressure is decreased compared to pore-
water pressure in the non-homogeneous earthen
dam with respect to distance. But starting and
ending point of seep is same. A silty clay is more
permeable compared to clay. Clay is less
permeable. In most cases clay is impermeable.
As a result, the velocity of flow is more in a
homogeneous dam, and in a non-homogeneous
dam, flow is approximately linear with respect to
distance. In homogeneous earthen dam, the
gradient is increased at the beginning compared
to the non-homogeneous earth dam but at the
critical section, velocity is decreased and the
gradient is also decreased compared to a non-
homogeneous earthen dam. At the downstream
point both for a homogeneous and non-
homogeneous earthen dam, gradient meets at a
certain point.
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(a)
(b)
(c)
Figure 8: Relationship between distance and flow parameters: (a) pore-water pressure vs. distance;
(b) velocity vs. distance; (c) gradient vs. distance.
0
10
20
30
40
50
60
0 5 10 15 20 25 30
Pore-water pressure (kpa)
Distance (m)
homogeneous non-homogeneous
0.00E+00
1.00E-06
2.00E-06
3.00E-06
4.00E-06
5.00E-06
6.00E-06
7.00E-06
8.00E-06
9.00E-06
0 5 10 15 20 25 30
velocity (m/sec)
Distance (m)
homogeneous non-homogeneous
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 5 10 15 20 25 30
Gradient
Distance (m)
homogeneous non-homogeneous
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Effect of horizontal blanket filter
When the filter is used in an earthen
dam in Fig. 2, the seepage line is pushed down.
It is produced a parabolic shape just near its
junction. It is observed that pore water pressure
in a homogeneous and non-homogeneous
earthen dam is slightly different before 15m.
After crossing the 15m both dams shows a linear
line. But the velocity of liquid passing through
both dams is quite different. The velocity of
seepage flow is increased in the homogeneous
dam as silty clay is used both in earthen dam and
foundation. It is proved that a horizontal blanket
filter is a factor which is controlled the pore
water pressure in a dam body.
(a)
(b)
0
10
20
30
40
50
60
0 5 10 15 20 25 30
pore-water pressure (kpa)
Distance (m)
homogeneous non-homogeneous
0.00E+00
1.00E-06
2.00E-06
3.00E-06
4.00E-06
5.00E-06
6.00E-06
7.00E-06
0 5 10 15 20 25 30
velocity (m/sec)
Distance (m)
homogeneous non-homogeneous
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(c)
Figure 9: Relationship between distance and flow parameters when horizontal blanket filter is
applied: (a) pore water pressure vs. distance; (b) velocity vs. distance; (c) gradient vs. distance.
Effect of horizontal filter
The horizontal filter is used in the
downstream side of an earthen dam shown in
Fig. 3 and consists of a comparatively higher
coefficient of permeability materials. In a
horizontal filter, the liquid is passed through a
specified path. In a homogeneous earthen dam as
well as a non-homogeneous earth dam, pore
water pressure is formed a parabolic shape
before meeting at the junction. Water passing
through seep is maximum in the homogeneous
earthen dam. As a result, velocity is also
maximum in the homogeneous dam compared to
the non-homogeneous dam. In both, the dam
condition gradient is increased. But after a
certain point, it falls down quickly.
(a)
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0 5 10 15 20 25 30
Gradient
Distance (m)
homogeneous non-homogeneous
0
10
20
30
40
50
60
0 5 10 15 20 25 30
pore-water pressure (kpa)
Distance (m)
homogeneous non-homogeneous
23
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(b)
(c)
Figure 10: Relationship between distance and flow parameters when horizontal filter is applied: (a)
pore water pressure vs. distance; (b) velocity vs. distance; (c) gradient vs. distance.
Effect of horizontal filter combined with rock
toe
Horizontal filter combined with rock toe
is shown in Fig. 4. A horizontal filter is applied
combined with rock toe to prevent seepage
failure. In the previous section, the horizontal
filter is analyzed alone. By using a horizontal
filter combined with rock toe, pore water
pressure is not differed more both for the
homogeneous and non-homogeneous earthen
dam. But the velocity of flow is more in a
homogeneous earthen dam compared to a non-
homogeneous earthen dam. The gradient is also
changed simultaneously in both dams.
0.00E+00
1.00E-06
2.00E-06
3.00E-06
4.00E-06
5.00E-06
6.00E-06
7.00E-06
8.00E-06
0 5 10 15 20 25 30
velocity (m/sec)
Distance (m)
homogeneous non-homogeneous
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
0 5 10 15 20 25 30
gradient
Distance(m)
homogeneous non-homogeneous
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(a)
(b)
(c)
Figure 11: Relationship between distance and flow parameters when horizontal filter combined with
rock toe is applied: (a) pore water pressure vs. distance; (b) velocity vs. distance; (c) gradient vs.
distance.
0
10
20
30
40
50
60
0 5 10 15 20 25 30
pore-water pressure (kpa)
Distance (m)
homogeneous non-homogeneous
0.00E+00
1.00E-06
2.00E-06
3.00E-06
4.00E-06
5.00E-06
6.00E-06
7.00E-06
0 5 10 15 20 25 30
velocity (m/sec)
Distance (m)
homogeneous non-homogeneous
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0 5 10 15 20 25 30
gradient
Distance(m)
homogeneous non-homogeneous
25
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Effect of rock toe
Rock toe consists of different types of
layers as shown in Fig. 5. Different types of
materials are used in different layers (such as
fine sand, coarse sand, gravel). According to
their permeability, the flow parameters are
changed. In the homogeneous earthen dam, pore
water pressure is decreased. But the rate of
decrease is more in a non-homogeneous earth
dam. In non-homogeneous earth dam clay is
applied to the foundation. For this the flow
velocity is less in a non-homogeneous earth
dam. Flow velocity is high in the homogeneous
dam. As water flows through the dam body as
well as foundation. The gradient is also changed
abruptly both in the homogeneous and non-
homogeneous earth dam.
(a)
(b)
0
10
20
30
40
50
60
0 5 10 15 20 25 30
pore-water pressure (kpa)
Distance (m)
homogeneous non-homogeneous homogeneous non-homogeneous
0.00E+00
2.00E-06
4.00E-06
6.00E-06
8.00E-06
1.00E-05
1.20E-05
0 5 10 15 20 25 30
velocity (m/sec)
Distance (m)
homogeneous non-homogeneous homogeneous non-homogeneous
26
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(c)
Figure 12: Relationship between distance and flow parameters when rock toe is applied: (a) pore
water pressure vs. distance; (b) velocity vs. distance; (c) gradient vs. distance.
Effect of internal clay core
When an internal clay core is applied in
an earthen dam shown in Fig. 6 and it is carried
approximately impermeable clay, their variation
of liquid flow parameters is noticeable. In the
homogeneous earthen dam, pore water pressure
is decreased from upstream to downstream and
the flow rate of velocity of water is higher
compared to a non-homogeneous dam. Because,
in the homogeneous dam, both earth dam and
foundation is used silty clay. There is no abrupt
change. The gradient also is changed slowly.
But, the non-homogeneous dam, contained silty
clay as a dam body and clay in the foundation as
well as in the internal clay core. For this reason,
at the beginning pore water pressure is changed
linearly up to a certain point and then changed
abruptly for the internal clay core. Then, the
flow is linear. The gradient also changed
suddenly in a non-homogeneous earthen dam
because of the internal clay core.
(a)
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0 5 10 15 20 25 30
Gradient
Distance (m)
homogeneous non-homogeneous homogeneous non-homogeneous
0
10
20
30
40
50
60
0 5 10 15 20 25 30
pore-water pressure (kpa)
Distance (m)
homogeneous non-homgeneous homogeneous non-homogeneous
homogeneous non-homogeneous homogeneous non-homogeneous
27
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(b)
(c)
Figure 13: Relationship between distance and flow parameters when internal clay core is applied: (a)
pore water pressure vs. distance; (b) velocity vs. distance; (c) gradient vs. distance.
Effect of transition filter
Transition filter is applied at the center
position of an earthen dam in Fig. 7. It is built
with highly permeable materials. It helps to
control the seepage flow. For a homogeneous
dam, a full transition filter provides a great rule.
The pore water pressure is changed abruptly as
the flow of water is high. The gradient is also
changed as fast. But, in non-homogeneous dam
pore water pressure is decreased continuously as
clay is applied in the foundation. Clay is less
permeable compared to silty clay.
0.00E+00
1.00E-06
2.00E-06
3.00E-06
4.00E-06
5.00E-06
6.00E-06
7.00E-06
8.00E-06
0 5 10 15 20 25 30
velocity (m/sec)
Distance (m)
homogeneous non-homogeneous homogeneous non-homogeneous
homogeneous non-homogeneous homogeneous non-homogeneous
-0.2
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1.8
0 5 10 15 20 25 30
Gradient
Distanec (m)
homogeneous non-homogeneous homogeneous non-homogeneous
homogeneous non-homogeneous homogeneous non-homogeneous
28
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(a)
(b)
(c)
Figure 14: Relationship between distance and flow parameters when transition filter is applied: (a)
pore water pressure vs. distance; (b) velocity vs. distance; (c) gradient vs. distance.
0
10
20
30
40
50
60
0 5 10 15 20 25 30
pore-water pressure (kpa)
Distance (m)
homogeneous non-homogeneous homogeneous non-homogeneous
0.00E+00
5.00E-06
1.00E-05
1.50E-05
2.00E-05
2.50E-05
3.00E-05
0 5 10 15 20 25 30
velocity (m/sec)
Distance (m)
homogeneous non-homogeneous homogeneous non-homogeneous
-0.5
0
0.5
1
1.5
2
0 5 10 15 20 25 30
gradient
Distance (m)
homogeneous non-homogeneous homogeneous non-homogeneous
29
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CONCLUSION
From the above analysis, it is clearly
seen that there is a difference in characteristics
both in the homogeneous and in a non-
homogeneous earthen dam. When filter media is
provided this difference increased more. From
this difference some key points are noted below:
1. The coefficient of permeability is a major
factor in the seepage analysis. The seepage
rate is more through higher permeable
materials.
2. Dam failure can be controlled by providing
different types of filter media, internal clay
core, rock toe, etc.
3. As the distance is increased, the seepage
flow is decreased. Thus, flow parameters
are changed according to distance.
4. The seepage rate is greatly changed when
the core is applied. Without applying core
there changed both for homogeneous and
non-homogeneous is negligible. After
providing core their difference is
noticeable.
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