DYNAMIC RESPONSE OF CONCRETE GRAVITY DAM ON RANDOM SOIL

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 6, Issue 11, Nov 2015, pp. 21-31, Article ID: IJCIET_06_11_003
Available online at
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=11
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
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___________________________________________________________________________
DYNAMIC RESPONSE OF CONCRETE
GRAVITY DAM ON RANDOM SOIL
Atheer Zaki Mohsin
PhD Candidate, Building and Construction Engineering Department,
University of Technology
Dr. Hassan Ali Omran
Asst. Prof., Building and Construction Engineering Department,
University of Technology
Dr. Abdul-Hassan K. Al-Shukur
Prof., Civil Engineering Department, College of Engineering,
University of Babylon
ABSTRAT
This research reports the dynamic response of a concrete gravity dam
under seismic excitation including dam‒reservoir‒foundation interaction. A
peek ground accelerations PGAS of 0.6ghas been applied on a numerical
model of the gravity dam that is built by finite element method using ANSYS.
In this model, the dam is considered as a rigid body, the reservoir as
compressible in viscid fluid, and the foundation as a random soil. A
parametric study is achieved through change of relative density (Dr) of
ground soil, namely, Dr= 60% and 80%. Modal and transient analyses have
been considered to achieve the results. The results are analyzed and compared
with experimental ones. It is shown a significant variation in the estimated
seismic response when the interaction is included in analyses.
Key words: Concrete gravity dam, Dam-reservoir-foundation interaction,
dynamic response, hydrodynamic pressure, Random soil
Cite this Article: Mohsin, A. Z., Dr. Omran, H. A. and Dr. Al-Shukur, A.-H. K.
Dynamic Response of Concrete Gravity Dam on Random Soil. International
Journal of Civil Engineering and Technology, 6(11), 2015, pp. 21-31.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=6&IType=11
_____________________________________________________________________
1. INTRODUCTION
Gravity dams form a lifeline of a country economy and their failure will create huge
loss of life and properties. Some of dams are in seismically active area. The dynamic

Atheer Zaki Mohsin,
Dr. Hassan Ali Omranand Dr.Abdul-Hassan K. Al-Shukur
analysis of a concrete gravity dam is a reasonably complex problem and hence its
behavior under seismic actions due to earthquakes has become a matter of immense
interest by the researchers.
The dynamic response of concrete gravity dam including dam-reservoir-
foundation interaction problems subjected to earthquake excitation could be simulated
numerically using finite element analysis software ANSYS.[1] used ANSYS
computer program to simulate the interaction of reservoir water-dam structure and
foundation bed rock. The analytical results obtained from over twenty 2D finite
element modal analysis of concrete gravity dam showed that the accurate modeling of
dam-reservoir-foundation and their interaction considerably affects the modal periods,
mode shapes and modal hydrodynamic pressure distribution. [2] used finite element
software ANSYS to simulate a two-dimensional model of gravity dam including dam-
water-foundation rock interaction to find a dynamic response ( natural frequency and
mode shape) for different shape of dams and the results are verified with other ones.
In the same matter, [3] found that considering dam-reservoir-foundation rock
interaction had an important role for safely designing a gravity dam. They used finite
element software ANSYS to simulate a two-dimensional model of gravity dam to
achieve these issues. To assess the accuracy of this modeling, the modal analysis and
mode shapes are studied and the results are compared with other references results.
Numerous of concrete gravity dam need to be constructed on soft soil. In this case,
a particular attention to be given to the problems of soil-structure interaction.
Therefore, [4] study the effect on gravity dam where is completely resting on soil
media and surrounded by soil media by using finite element analysis software
ANSYS. In her research the relevant amount of soil around and bottom of the gravity
dam has been modeled to simulate the in-situ conditions. Also, the dynamic loading in
transient analysis is considered to carry out the influence of soil properties on the
response of dam in terms of stress and deformation.
This paper aims to investigate on dynamic responses of optimized concrete
gravity dam section on random soil including dam‒reservoir‒foundation interaction
subjected to earthquake excitations.
To achieve this aim, the research is organized as follows: Section 2 describes the
model of the dam that is built by ANSYS, the governing equations, the related
parameters and materials, and the suitable elements to mesh the model and solve the
problem. The dynamic response concepts and analyses are presented in section 3. The
parametric studies that will depend to achieve this research are also considered in this
section. The obtained results are presented in Section 4. Moreover, these results are
analyzed and discussed in this section. The conclusions and recommendations are
presented in Sections 5 and 6, respectively.
2. MODEL OF THE DAM BY ANSYS
The section of dam that is modeled by ANSYA is shown in Fig. (1).In this figure the
secant pile are considered beneath dam to serve as a barrier to reduce seepage beneath
dam, as a device to improve bearing capacity of soil, and as a key under base of dam
to overcome both sliding and overturning.

Dynamic Response of Concrete Gravity Dam on Random Soil
Figure 1 Prototype Dam Model [After[5]]
The dam section is optimized to achieve all factors of safety and stability
requirements. Table (1) gives the optimal dimensions of both dam and pile sections.
Table 1 Optimized Dam& Pile Sections[After [5]]
The properties of materials that used to build the model could be given in Table
(2-a,b, and c) to represent the properties each of concrete of dam body, water
reservoir, and soil foundation.
Table 2 Properties of Materials [After [5]]
The 2D finite element model of the problem is discretized by ANSYS APDL15.0
and it is shown in Fig. (2).
Figure 2 Finite element discretization of model

Atheer Zaki Mohsin,
In this figure, the elements shall be used are: four‒nodes PLANE 42 element
(structural 2D solids) plain strain, shown in Fig. 3 which available in ANSYS 15.0 is
used for both dam body and soil foundation modeling. This element represents
equation of a structural dynamics given in Eg. (1) [6] and [7]
(1)
Where , , and are the structural mass, damping and stiffness matrices,
respectively, is the nodal displacement vector with respect to ground and the term
represents the nodal force vector associated with the hydrodynamic pressure
produced by the reservoir.
Figure 3 PLANE42 Element Geometry [6]
Also, the interface of the soil‒structure interaction problem that is expressed
numerically by coupling equation (Eq. 1) can be discretize by making NUMMRGE
command for all nodes and elements on the contact surfaces ( interaction planes ) or
by CONTA172 and TARGE 169 elements which making a SURF in between them.
CONTA172 is used to represent contact and sliding between 2D "target" surfaces
(TARGE169) and a deformable surface, defined by this element. The element is
applicable to 2D structural and coupled field contact analyses. This element is located
on the surfaces of 2D solid elements with midside nodes. It has the same geometric
characteristics as the solid element face with which it is connected Fig.4. Contact
occurs when the element surface penetrates one of the target segment elements
(TARGE169) on a specified target surface. Coulomb and shear stress friction is
allowed. This element also allows separation of bonded contact to simulate interface
delamination. TARGE169, Fig.5, is used to represent various 2D "target" surfaces for
the associated contact elements. The contact elements themselves overlay the solid
elements describing the boundary of a deformable body and are potentially in contact
with the target surface, defined by TARGE169. This target surface is discretized by a
set of target segment elements (TARGE169) and is paired with its associated contact
surface via a shared real constant set. It can impose any translational or rotational
displacement, temperature, voltage, and magnetic potential on the target segment
element. Also, it can impose forces and moments on target elements.
Figure 4 CONTA172 Geometry [6]

Figure 5 TARGE169 Geometry [6]
In other hand, a four-node FLUID 29 element shown in Fig. (6) is used to discretize
both fluid and coupled fluid‒structure interaction domains represented by Eq. (2).
Figure 6 FLUID29Element Geometry [6]
(2)
Where: = and =
3. DYNAMIC RESPONSE
The dynamic response represents modal analyses for mode shapes and natural
frequencies. Also, von misses stresses, pressure on reservoir (hydrodynamic), and
displacement have been considered. In other hand, a transient analysis is also
considered in the dynamic response of the dam where a PGA of 0.6g as a transient
load is applied. In this type of analysis, the displacements on the top, middle and
down of the dam will be calculated.
In order to include a parametric study in this research, the characteristics of soil
have been changed. The modulus of elasticity of soil have been selected so could
range in-between medium to densemedia of sand soil with relative densities 60% and
80% respectively as given in Table (3).
Table 3 Denseness of soils[After [8]]

Atheer Zaki Mohsin,
Mode1 Mode3 Mode5
Mode1 Mode3 Mode5
(a) Deformation
Mode1 Mode3 Mode5
(b) Displacement
Mode1 Mode3 Mode5
(c) Pressure
Mode1 Mode3 Mode5
(d) Stress
Figure 7 Mode shapes of the dam for medium sand soil Dr=60%

Mode1 Mode3 Mode5
Mode1 Mode3 Mode5
(a) Deformation
Mode1 Mode3 Mode5
(b) Displacement
Mode1 Mode3 Mode5
(c) Pressure
Mode1 Mode3 Mode5
(d) Stress
Figure 8 Mode shapes of the dam fordense sand soil Dr=80%
4. RESULTS AND DISCUSSIONS
As mentioned earlier, the parametric study is involved in the dynamic response of the
dam. The results will show the effects of soil with relative density (Dr) of 60%, and
80%.The results of the dynamic response could be categorized as given below:

Atheer Zaki Mohsin,
4.1. Modal analyses
In modal analysis where load is zero, the behavior of dam including dam-reservoir-
foundation interaction is represented through mode shapes and natural frequencies.
The number of mode is five, but the more effective modes results will be shown.
Moreover, displacement of the dam, dynamic pressure on reservoir (hydrodynamic),
and von misses stress of the dam are observed in these mode shapes as shown in Fig.
7 (a, b, c, and d) for Dr=60% and Fig. 8 (a, b, c, and d) for Dr=80%, respectively. The
results of modal analyses are summarized in Table (4).
Table 4 Natural frequency of modal analyses
Mode No.
Item
Mode 1 Mode 3 Mode 5
Dr=60%
Natural frequency(Hz) 144.08 216.00 239.41
Max. Displacement (m) 0.138ᵡ10-5
0.349ᵡ10-5
0.235ᵡ10-5
Max. Pressure (Pa) 729.525 1281.91 1041.28
Max. Stress (Pa) 33944.7 33367.2 13503.8
Dr=80%
Natural frequency(Hz) 858.64 1260.72 1485.55
Max. Displacement (m) 0.332ᵡ10-5
0.421ᵡ10-6
0.414ᵡ10-6
Max. Pressure (Pa) 4327.46 4942.51 5626.64
Max. Stress (Pa) 129555 14594.8 32926
To ensure accuracy of the results, the verification is made with experimental
results given in research of [9] as shown in Fig.9.
(b) Test-2(Dr=60%)(a) Test-1(Dr=80%)
Figure 9 Observations on dam after third phase-0.6g tests[After [9]]
The results show that the deformation (mode shape 3) of Fig. 7 (a) givea
reasonable compatible result with observation shown in Fig. 9 (b). Also, it is showed
that the behavior of dam on deformation (mode shapes) of Fig. 8 (a) gives somewhat
compatible results with the experimental observation result shown in Fig. 9 (a).
4.2. Transient analysis
Transient dynamic analysis (sometimes called time-history analysis) is a technique
used to determine the dynamic response of a structure under the action of any general

time-dependent loads. The transient analysis results from ANSYS for two parametric
studies include dynamic response of displacement in different locations on dam.
These locations are taken as located in the experimental work which symbolized by
LVDTs as shown in Fig. 10, where other dynamic responses are not considered in this
research.
Figure 10 Layout of locations of output dynamic responses transducers in the experimental
work [After [9]]
The dynamic response results for Dr=60% andDr=80% from ANSYS and
experimental work are shown in Fig. 11(a and b ) and12(a and b ), respectively.
(a) Displacement from ANSYS (b) Displacement from experimental work
After[9]
Figure 11 Dynamic responses on dam for Dr=60% from ANSYS andExperimental Work
It is shown from figs. 11 and 12 that there is almost compatible on dynamic
response of dam in between numerical analysis by ANSYS and experimental work
given in [9] with some differences with times especially between 3-4 sec.
5. CONCLUSIONS
A dynamic response including modal and transient analyses considering dam-
reservoir- random soil foundation interaction are investigated numerically. A 2D-plain
strain rigid dam model is built by using finite element computer programming
APDL/ANYS 15.0 taking water reservoir as an inviscid and compressible fluid and
flexible foundation of random and soil. To make a parametric study, two values
of the relative density namely Dr=60% and Dr=80% are taken to represent medium
-1.00
0.00
1.00
2.00
3.00
4.00
5.00
6.00
0 1 2 3 4 5 6 7 8 9 10
Displacement(cm)
Time (Sec)
LVDT1
-0.50
0.00
0.50
1.00
1.50
2.00
0 1 2 3 4 5 6 7 8 9 10
Displacement(cm)
Time (Sec)
LVDT2
-4.00
-3.00
-2.00
-1.00
0.00
1.00
0 1 2 3 4 5 6 7 8 9 10
Displacement(cm)
Time (Sec)
LVDT3

Atheer Zaki Mohsin,
and dense sand soil. The concrete gravity dam model is built to simulate exactly a
physical model construct experimentally given through a research in the literature.
The results are analyzed and compared with these of experimental work. It is
concluded the following:
(a) Displacement from ANSYS (b) Displacement from experimental work
[After[9]]
Figure 12 Dynamic responses on dam for Dr=80% from ANSYS and Experimental Work
The model that built by using ANSYS is efficient on the dynamic analyses of
concrete gravity dam under earthquake excitation.
Generally, the results are verified with other experimental work and give almost
compatible results.
The natural frequency of dam constructed on dense sand soil is more than by 80%
from this with medium soil due to difference in stiffens factor.
The modal analyses on dynamic response of dam gives the maximum
displacements of dam in the case of Dr=60% more by 85% than of case of Dr=80%
due to the flexibility of the first one.
The dynamic pressure (hydrodynamic) applied on the dam face in the case of
Dr=60% is little by 80% than of case of Dr=80% as a result of absorption of the wave
that impact the dam by water reservoir through earthquake by soil when it became
more loss.
The max von misses equivalent stresses in the case of Dr=60% concentrated on
the heel and toe of dam and on the position of the pile where increased by 70% more
than in the case of soil of Dr=80% where the stresses distributed in different positions
on dam and soil due to interaction in between them.
The liquefaction phenomenon is observed obviously incase of soil of Dr=60%
which is behaved as a saturated loss sandy clay soil.
The concrete gravity dam is more stable on soil of Dr=80% than on soil of
Dr=60%. The sliding and overturning are more effective in medium loss san soil than
this one in dense [10].
6. RECOMMENDATIONS
From the results obtained in this research, it is recommended the following:
-0.50
0.00
0.50
1.00
1.50
0 1 2 3 4 5 6 7 8 9 10
Displacement(cm)
Time (Sec)
LVDT1
-0.50
0.00
0.50
1.00
1.50
0 1 2 3 4 5 6 7 8 9 10
Displacement(cm)
Time (Sec)
LVDT2
-1.00
-0.80
-0.60
-0.40
-0.20
0.00
0.20
0 1 2 3 4 5 6 7 8 9 10
Displacement(cm)
Time (Sec)
LVDT3

Avoidance of construct this type of dam on random soil at region affected by
seismic zone of PGA=0.6g (Category V of moderate shaking and 4.5 of Richter
Scale) and more.
In the contrast, it is ability to construct this type of dam founded on random soil as
located on region affected by seismic zone of PGA= (0.01‒0.4)g (Category I, II-III,
and IV as Not felt, weak, and light shaking respectively that ranged 1-4 of Richter
Scale) with some precautions .
Construction of blanket of clay layer about 30 cm upstream dam to reduce
seepage flow through foundation.
Construct sheet of secant piles beneath dam to reduce seepage, pear the weight of
dam, and to prevent both sliding and overturning.
Avoidance of construct concrete gravity dam founded on saturated loss to medium
dense sand soil under effects of seismic zone.
REFERENCES
[1] Shariatmadar, H. and Mirhaj, A. Modal Response of Dam-Reservoir-Foundation
Interaction,8th International Congress on Civil Engineering, Shiraz University,
Shiraz, Iran ,May 11-13, 2009.
[2] Khosravi, S., Salajegheh, J. and Heydari, M. Simulating of Each Concrete
Gravity Dam with Any Geometric Shape Including Dam-Water-Foundation Rock
Interaction Using APDL. World Applied Sciences Journal, 17(3), 2012, pp. 354-
363.
[3] Khosravi, S. and Heydari, M. Simulating of Each Concrete Gravity Dam with
Any Geometric Shape Including Dam-Water-Foundation Rock Interaction Using
APDL. World Applied Sciences Journal, 22(4), 2013, pp. 538-546.
[4] Swapanal, P. Effect of Soil Structure Interaction on Gravity Dam. International
Journal of Science, Engineering and Technology Research (IJSETR), 4(4), 2015,
pp. 1046-1053.
[5] Mohsin, A. Z., Omran, H. A. and Al-Shukur, A-H. K. Optimal Design of Low
Concrete Gravity Dam on Random Soil Subjected to Earthquake Excitation.
International Journal of Innovative Research in Science, Engineering and
Technology (IJIRSET), 4(9), 2015, pp. 8961-8973.
[6] ANSYS. ANSYS User's Manual, ANSYS Theory Manual, Version 15.0, 2013.
[7] Paz, M. and Leigh, W. Structural Dynamics: Theory and Computation. USA:
Kluwer Academic Publishers, 2004.
[8] Rao, K. Foundation Design: Theory and Practice. John Wiley and sons (Asia) Pte
Ltd., 2011.
[9] Mohsin, A. Z., Omran, H. A. and Al-Shukur, A-H. K. Shaking Table Tests on a
Physical Model of a Conctete Gravity Dam. International Journal of Scientific
and Engineering Research (IJSER),6(9), 2015, pp. 1230-1237.
[10] Pathan, K. M. Finite Element Analysis of 99.60 M High Roller Compacted
Concrete (RCC) Gravity Dam - Special Emphasis on Dynamic Analysis.
International Journal of Civil Engineering and Technology, 3(2), 2012, pp. 387-
391.

DYNAMIC RESPONSE OF CONCRETE GRAVITY DAM ON RANDOM SOIL

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