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Tikrit Journal of Engineering Sciences Volume 30 No. 22023
41
Page
Tikrit Journal of Engineering Sciences (2023) 30 (2): 41-45
DOI: http://doi.org/10.25130/tjes.30.2.5
Effect of Core Geometry on Earth Dam Slope Stability
Yaseen W. Aziz
*, Arkan H. Ibrahim , Osama K. MohammedAmin
Department of Water Resources, College of Engineering, University of Salahaddin, Erbil, Iraq
.
Keywords:
Zoned Earth Dam; Slope Stability; Clay Core
ARTICLE INFO
Article history:
Received 24 Jan. 2023
Accepted 30 Mar. 2023
Received in revised form 12 Apr. 2023
Final Proofreading 05 May. 2023
Available online 06 May. 2023
©2023 COLLEGE OF ENGINEERING, TIKRIT
UNIVERSITY. THIS IS AN OPEN ACCESS
ARTICLE UNDER THE CC BY LICENSE
http://creativecommons.org/licenses/by/4.0/
Citation: Aziz YW, Ibrahim AH,
Mohammed-Amin OK. Effect of
Core Geometry on Earth Dam Slope
Stability. Tikrit Journal of Engineering
Sciences 2023; 30(2): 41-45.
http://doi.org/10.25130/tjes.30.2.5
*Corresponding author:
Yaseen W. Aziz
Department of Water Resources, College of
Engineering, University of Salahaddin, Erbil, Iraq.
Abstract: Embankment dams are widely
constructed due to their suitability with
different types of foundation, and it is
constructed from the available material a
t the
site. A zoned earth dam consists of a clay core at
the center to control seepage supported by a
shell. This paper investigated the impacts of
side slopes, top width, and shape on upstream
and downstream slope stability during different
cases. Slide 6
.0 software was used to evaluate
the factor of safety of side slopes of an earth
dam, and its result was validated. Different side
slopes range from 0H:1V to 2 H:1V, and crest
widths from 3m to 10 m were examined. In
addition, for the slanting core case, s
everal
cases with varying angles of inclination were
provided. The results indicated that by
increasing the side slopes of the core, the factor
of safety was reduced, especially in the steady
state and rapid drawdown conditions.
Increasing the top width al
so reduced the safety
factor in the steady state condition. This
reduction was because the core material had
lower shear strength than the shell material. In
addition, in a steady state and rapid drawdown
conditions, the cohesion of core material
sharply r
educed. Compared with the vertical
case, increasing the slanting core slopes
influenced the slope stability insignificantly
during the steady state. The slanting core had
benefits in the steady state when the reservoir
was full since, in this case, increas
ing core side
slopes affected the slope stability
insignificantly. The maximum core side slope in
the earth dam and maximum top width, which
insignificantly affected the dam’s slope stability,
were 0.8:1 and 5 m, respectively.
Yaseen W. Aziz, Arkan H. Ibrahim, Osama K. MohammedAmin / Tikrit Journal of Engineering Sciences 2023; 30(2): 41-45.
Tikrit Journal of Engineering Sciences Volume 30 No. 22023
42
Page
ﻲﺑارﺗﻟا دﺳﻠﻟ ﻲﺑﻧﺎﺟﻟا لﯾﻣﻟا رارﻘﺗﺳإ ﻰﻠﻋ بﻠﻟا لﻛﺷ رﯾﺛﺄﺗ
زﯾزﻋ وﺳو نﯾﺳﺎﯾ
، ةزﻣﺣ نﺎﻛرأ،مﯾھارﺑا ﺔﻣﺎﺳا نﯾﻣا دﻣﺣﻣ
ﻟا مﺳﻗ
ﺔﯾﺋﺎﻣﻟا دراوﻣ /ﺔﯾﻠﻛ ﺔﻌﻣﺎﺟ / ﺔﺳدﻧﮭﻟا نﯾدﻟا حﻼﺻ – ل ﯾ ﺑ ر ا/ قارﻌﻟا .
ﺔﺻﻼﺧﻟا
.ﻊﻗوﻣﻟا ﻲﻓ ﺔﺣﺎﺗﻣﻟا داوﻣﻟا نﻣ ﻰﻧﺑﺗ ثﯾﺣ ،تﺎﺳﺎﺳﻷا نﻣ ﺔﻔﻠﺗﺧﻣ عاوﻧﻷ ﺎﮭﺗﻣءﻼﻣ بﺑﺳﺑ ﻊﺳاو قﺎطﻧ ﻰﻠﻋ ﺔﯾﺋﻼﻣﻻا دودﺳﻟا ءﺎﻧﺑ مﺗﯾ
ﻓ .فﻼﻐﺑ طﺎﺣﯾو برﺳﺗﻟا ﻰﻠﻋ ةرطﯾﺳﻠﻟ زﻛرﻣﻟا ﻲﻓ ﻲﻧﯾط بﻟ نﻣ تﺎﻘﺑطﻟا وذ ﻲﺑارﺗﻟا دﺳﻟا نوﻛﺗﯾ تارﯾﺛﺄﺗ ﺔﺳارد مﺗ ثﺣﺑﻟا اذھ ﻲ
مادﺧﺗﺳا مﺗ .ﺔﻔﻠﺗﺧﻣ تﻻﺎﺣ لﻼﺧ رﺧؤﻣﻟاو مدﻘﻣﻟا ﻲﻓ تاردﺣﻧﻣﻟا رارﻘﺗﺳا ﻰﻠﻋ لﻛﺷﻟاو ،دﺳﻟا ﺔﻣﻗ ضرﻋ ،بﻠﻟ ﺔﯾﺑﻧﺎﺟﻟا تاردﺣﻧﻣﻟا
ﺞ ﻣ ﺎ ﻧ ر ﺑSlide 6.0 ﻧﺎﺟ تاردﺣﻧﻣ ةدﻋ رﺎﺑﺗﺧا مﺗ .ﮫﺗﺣﺻ نﻣ ﻖﻘﺣﺗﻟا مﺗو ،ﻲﺑارﺗ دﺳﻠﻟ ﺔﯾﺑﻧﺎﺟﻟا تاردﺣﻧﻣﻟا نﺎﻣأ لﻣﺎﻌﻣ مﯾﯾﻘﺗﻟ
ﺔﯾﺑ
) نﯾﺑﺎﻣ تﺣوارﺗ بﻠﻟ ﺔﻔﻠﺗﺧﻣ
0H:1V) ﻰﻟإ (2H:1V نﻣ ﺔﻣﻗ ضرﻋو (3 ﻰﻟإ م10
ﺔﯾﺳﺎﺳﻷا ﺔﻟﺎﺣﻠﻟ ﺔﺑﺳﻧﻟﺎﺑ ،كﻟذ ﻰﻟإ ﺔﻓﺎﺿﻹﺎﺑ .م
لﻣﺎﻌﻣ نﺈﻓ بﻠﻟ ﺔﯾﺑﻧﺎﺟﻟا تاردﺣﻧﻣﻟا ةدﺎﯾز لﻼﺧ نﻣ ﮫﻧأ ﻰﻟإ ﺞﺋﺎﺗﻧﻟا ترﺎﺷأ .ﺔﻔﻠﺗﺧﻣ لﯾﻣ ﺎﯾاوزﺑ تﻻﺎﺣﻟا نﻣ دﯾدﻌﻟا رﯾﻓوﺗ مﺗ ،ﺔﻠﺋﺎﻣﻟا
ﺔﺻﺎﺧ ،ضﻔﺧﻧا نﺎﻣﻷا
ﺎًﺿﯾأ يوﻠﻌﻟا ضرﻌﻟا ةدﺎﯾز يدؤﺗ .دﺳﻟا هﺎﯾﻣ بوﺳﻧﻣﻟ ءﻲﺟﺎﻔﻣﻟا طوﺑﮭﻟا ﺔﻟﺎﺣ وا ةرﻘﺗﺳﻣﻟا ﺔﻟﺎﺣﻟا فورظ ﻲﻓ
ةدﺎﻣ نﻣ لﻗأ صﻗ ﺔﻣوﺎﻘﻣ ﺎﮭﯾدﻟ بﻠﻟا ةدﺎﻣ نأ بﺑﺳﺑ وھ نﺎﻣﻻا لﻣﺎﻌﻣ ﻲﻓ نﺎﺻﻘﻧﻟا اذھ نإ .رارﻘﺗﺳﻻا ﺔﻟﺎﺣ ﻲﻓ نﺎﻣﻷا لﻣﺎﻌﻣ لﯾﻠﻘﺗ ﻰﻟإ
ﻻا ﺔﻟﺎﺣ ﻲﻓ ،كﻟذ ﻰﻟإ ﺔﻓﺎﺿﻹﺎﺑ .فﻼﻐﻟا ﺔﻧرﺎﻘﻣ .رﯾﺑﻛ لﻛﺷﺑ ﺔﯾﺳﺎﺳﻷا داوﻣﻟا كﺳﺎﻣﺗ ضﻔﺧﻧا دﺳﻟا هﺎﯾﻣﻟ ﻊﯾرﺳﻟا طوﺑﮭﻟا فورظو رارﻘﺗﺳ
بﻠﻟا نأ ﺞﺋﺎﺗﻧﻟا تﻧﯾﺑ .ةرﻘﺗﺳﻣﻟا ﺔﻟﺎﺣﻟا ءﺎﻧﺛأ لﯾﺋﺿ لﻛﺷﺑ دﺳﻟا لوﯾﻣ رارﻘﺗﺳا ﻰﻠﻋ رﺛأ لﺋﺎﻣﻟا بﻠﻟا لﯾﻣ ةدﺎﯾز نﺈﻓ ،ﺔﯾدوﻣﻌﻟا ﺔﻟﺎﺣﻟﺎﺑ
ﻟا نوﻛﯾ ﺎﻣدﻧﻋ ةرﻘﺗﺳﻣﻟا ﺔﻟﺎﺣﻟا ﻲﻓ دﺋاوﻓ ﮫﻟ لﺋﺎﻣﻟا ردﺣﻧﻣﻟا رارﻘﺗﺳا ﻰﻠﻋ لﺋﺎﻣﻟا بﻠﻟا لﯾﻣ ةدﺎﯾز ترﺛأ ،ﺔﻟﺎﺣﻟا هذھ ﻲﻓ ﮫﻧﻷ ،ﺎًﺋﻠﺗﻣﻣ نازﺧ
ﻰﻠﻋ لﯾﺋﺿ لﻛﺷﺑ رﺛأ يذﻟاو دﺳﻟا ﺔﻣﻗ ضرﻌﻟ ﻰﺻﻗﻷا دﺣﻟاو ﻲﺑارﺗﻟا دﺳﻟا ﻲﻓ بﻠﻟ ﻲﺑﻧﺎﺟﻟا لﯾﻣﻠﻟ ﻰﺻﻗﻷا دﺣﻟا نﺎﻛ .لﯾﺋﺿ لﻛﺷﺑ
) وھ دﺳﻟا ردﺣﻧﻣ رارﻘﺗﺳا
0.8:1 و (5 .ﻲﻟاوﺗﻟا ﻰﻠﻋ رﺎﺗﻣأ
:ﺔﻟادﻟا تﺎﻣﻠﻛﻟا ﻲﻧﯾطﻟا بﻠﻟا ،تاردﺣﻧﻣﻟا ﺔﯾرارﻘﺗﺳا ،تﺎﻘﺑطﻟا وذ ﻲﺑارﺗﻟا دﺳﻟا.
1.INTRODUCTION
Earth dams are barriers constructed across
rivers to store water. They are constructed from
fragmental natural materials available at the
site, and the earth dams are classified into
homogeneous and zoned earth dams [1]. The
zoned earth dam consists of a central
impervious core supported by a shell of
previous material, and a transition filter is
provided between the shell and core. The main
problems of earth dams are excessive seepage
and sliding of side slopes USBR [2]1988). The
core and shell dimensions are usually
determined by the types of soils and their
available quantities at the dam site [3]. Mainly
the core dimensions should have an
insignificant influence on the slope stability and
control seepage quantity. [4] (Datta & Gulhati,
1991) analyzed the influence of the core’s side
slopes and top width on the earth dam slope
stability. In addition, the study provided a limit
for the core side slope, which beyond this limit,
it has a significant influence on the slope
stability. Furthermore, to control the seepage
core at the zoned earth dams, they were
provided with different shapes, such as vertical
and slanting with different side slopes, Which
vertical and slanting have their advantages and
disadvantages [5]. The inclined core behaved
better thn he vertical core, especially important
settlements during the dam body construction.
[6] (Rajesh et al, 2011) investigated the effect of
a vertical core side slope on slope stability. The
authors concluded that the factor of safety of
upstream and downstream slopes was reduced
by increasing the side slopes to more than
1:1.5V. The safety factor of the zoned earth dam
side slopes increased as the core width reduced
because the core material had lower shear
strength than the shell material and had higher
pore water pressure [7]. The present study
investigated the effect of side slopes, top width,
and shape of the core (slanting and vertical) of
core material on the slope stability of upstream
and downstream slopes for different cases.
Different side slopes, top widths, and slanting
shapes were analyzed using Slide 6.0 software.
2.MATERIAL AND METHODS
2.1.Slide 6.0 Software
To investigate the effect of the core side slopes
in vertical and slanting cases on upstream and
downstream slope stability during different
cases, Slide 6.0 was utilized. The 2D software is
based on limit equilibrium for the estimation
factor of safety for circular and non-circular
failure surfaces [8]. The software analyzes slip
surfaces using vertical and non-vertical slices.
In addition, it has many methods to analyze
groundwater. The software uses finite element
analysis to predict a water table in earth dams
and any hydraulic structure.
2.2.Description of the Dam
In this study, the Degala earth fill dam analyzed
the side slope effect and the core shape on the
upstream and downstream slope stability.
Degala dam is located in Degala village on Koya
road, about 35 km from Erbil city center (Fig.1).
The dam is a zoned earth fill dam with a 32 m
height; its cross-section is shown in Fig. 2. It
consists of a clay core supported by a shell with
an upstream slope of 1V:2.5H and a
downstream slope of 1V:2.75H. There is a
transition filter with 0.8m between the dam’s
core and shell. The properties of the Degala
dam materials are presented in Table 1. In the
present study, the vertical core’s different side
slopes ranged from 0H:1V to 2H:1V, and seven
different top widths were considered. In
addition, for the slanting (inclined) core, eleven
Yaseen W. Aziz, Arkan H. Ibrahim, Osama K. MohammedAmin / Tikrit Journal of Engineering Sciences 2023; 30(2): 41-45.
Tikrit Journal of Engineering Sciences Volume 30 No. 22023
43
Page
cases were considered with different upstream
side slopes.
Fig. 1 Degala Dam View.
Fig. 2 Cross Section of Degala Dam.
Table 1 Degal Dam Material Properties.
Materials
End of Construction
Steady State
K
C
(KN/m
2
)
Φ
(Degree)
C
(kN/m
2
)
Φ
(Degree)
m/s
Shell
3
41
3
41
1*10-4
Core
200
0
80
5
9.8*10-7
Filter
0
32
0
32
1*10-3
Foundation 1
100
5
100
5
2.5*10-5
Foundation 2
3000
0
3000
0
1*10
-7
3.RESULTS AND DISCUSSION
3.1.Validation of Results
To validate and evaluate the applicability of the
software used in the present study, the results
were compared with some methods from the
literature. The slope stability results predicted
by Slide 6.0 were compared with two analyses
performed for the construction condition end of
the Clearance Cannon dam section. The dam
cross-section consists of two phases of
compacted clay. The analysis was performed by
[9, 10]. The results comparison of the factor of
safety of the downstream slope for end
construction condition is shown in Table 2. The
comparison showed a good agreement between
results. The Slide 6.0 software result was very
close to other methods, and the software
accurately evaluated the slope stability.
Table 2 Comparison Results between Slide
6.0 and Two other Methods.
Model
Minimum Downstream FOS
Hassan and Wolf (1999)
2.647
Bhattacharya et al, (2003)
2.612
Slide 6.0
2.61
3.2.Effect of Core Slope on the Vertical
Case Slope Stability
The upstream and downstream slopes of the
dam were tested for different core slopes during
different cases, i.e., end of construction for
upstream and downstream, Steady state
downstream, and rapid drawdown of upstream.
This analysis examined 17 different core slopes,
ranging from (0H:1V to 2H:1V) . Two cases of
the sloping upstream and downstream and
vertical core are shown in Figs. (2, 3). The
summary of the slope stability results for
different cases is presented in Table 3.
Fig. 2 Steady-State Condition (Vertical Core
1.1H:1V).
Fig. 3 After Construction Condition DS
(Vertical Core 0H:1V).
Table 3 Results of FOS Changing Core Side
slopes.
Core
Slope
After Construction
Steady
State
Rapid
drawdown
US
DS
DS
US
0H:1V
2.273
2.332
2.274
1.111
0.1H:1V
2.273
2.331
2.186
1.111
0.2H:1V
2.271
2.331
2.032
1.11
0.3H:1 V
2.271
2.33
1.873
1.103
0.4H:1V
2.251
2.327
1.765
1.102
0.5H:1V
2.197
2.305
1.676
1.103
0.6H:1V
2.132
2.257
1.599
1.102
0.7H:1 V
2.101
2.225
1.545
1.103
0.8H:1 V
2.103
2.207
1.505
1.103
0.9H:1V
2.124
2.213
1.482
1.102
1H:1V
2.152
2.238
1.476
1.18
1.1H:1V
2.177
2.265
1.478
1.11
1.2H:1V
2.201
2.213
1.479
1.115
1.4H:1V
2.245
2.269
1.481
1.082
1.6H:1V
2.22
2.344
1.482
1.049
1.8H:1V
2.172
2.296
1.481
1.023
2H:1V
2.134
2.199
1.478
0.999
As can be observed from Table 3, initially, as the
core upstream and downstream slope
increased, the safety factor reduced because the
shear strength of the core material was lower
than the shell material shear strength. The
reduction of safety factor (FOS) with respect to
all cases was different. From after construction
loading condition, the minimum factor of safety
corresponding to maximum core side slope is
greater than critical value of safety factor.
However, in the steady state case, the reduction
was significant, and the factor of safety was less
than the critical value at core side slopes
(0.9H:1V). At rapid drawdown, the safety factor
insignificantly reduced as the core side slope
increased; its value was less than the critical
value at the core side slopes (1.4H:1V). The
summary of results showed that the core side
slope of (0.8H:1V) was a critical value, and
more than this value, the slope became
unstable.
Yaseen W. Aziz, Arkan H. Ibrahim, Osama K. MohammedAmin / Tikrit Journal of Engineering Sciences 2023; 30(2): 41-45.
Tikrit Journal of Engineering Sciences Volume 30 No. 22023
44
Page
3.3. Effect of Top Width of Core on Slope
Stability
In this case, the top width of the clay core was
changed, while the sides slopes were fixed. The
results showed that increasing the top width
insignificant influenced the slope stability at the
upstream and downstream slope during the end
of construction and upstream slope during
rapid drawdown. However, in the steady state
case, the FOS reduced as the top width
increased due to increasing the core area, which
had lower shear strength while higher pore
water pressure. Also, this case was much more
sensitive than other cases, such as rapid
drawdown for changing material properties
(Table 4).
Table 4 Results of the FOS Changing Core
Top Width.
Core
Width
(m)
After Construction
Steady
State
Rapid
drawdown
US
DS
DS
US
3
2.239
2.345
2.037
1.109
4
2.239
2.345
2.013
1.109
5
2.237
2.345
1.984
1.109
6
2.273
2.345
1.959
1.109
7
2.273
2.345
1.942
1.109
8
2.273
2.358
1.927
1.109
9
2.273
2.358
1.911
1.109
10
2.273
2.358
1.89
1.109
3.4.Effect of Core Slope on Slope
Stability in Slanting Case
To investigate the effect of the core shape on
slope stability, several runs were performed for
inclined cores with different upstream and
downstream side slopes. In the analysis, 11 core
cases were investigated by changing the
upstream core slope from (0.1H:1V) to
(2.2H:1V) and fixing the downstream core
slope. It started from a slope of 0.12H:1V for
case 1 and to a slope of 2.2H:1V for case 11. The
results of the factor of safety for different side
slopes of the inclined core are presented in
Table 5.
Table 5 Results of the FOS Slanting Core Cases.
Slanting
Core cases
After
Construction
Steady
State
Rapid
drawdown
US
DS
DS
US
1
2.273
2.332
2.275
1.143
2
2.273
2.332
2.275
1.141
3
2.273
2.384
2.275
1.111
4
2.245
2.332
2.275
1.109
5
2.173
2.332
2.237
1.049
6
2.032
2.332
2.275
1.141
7
2.009
2.332
2.275
1.109
8
2.045
2.332
2.275
1.137
9
2.083
2.332
2.275
1.092
10
2.152
2.332
2.275
1.003
11
2.103
2.332
2.275
0.993
It is clear that from the results of the factor of
safety for different cases of inclined core,
during the end of construction condition,
changing the slope of the upstream core had an
insignificant effect on the downstream slope;
however, the factor of safety for the upstream
part reduced by increasing the upstream slope
of the core. For steady state condition, the
factor of safety was almost constant since, in the
inclined core case, all the core sections were
located at the upstream part of the dam section,
so changing the side slope had an insignificant
effect on the downstream slope. During the
rapid drawdown condition, by increasing the
core’s upstream slope, the factor of safety
decreased because of increasing the core area at
upstream and pore water pressure. Compared
with the vertical case, the FOS during the steady
state through changing slope of the core was
constant. However, in the vertical case, FOS
was reduced by changing the core slope (Fig. 4).
Fig. 4 FOS During the Steady State for
Inclined and Vertical Core.
4.CONCLUSIONS
The present study investigated the effects of
core shape and dimensions on different cases of
slope stability upstream and downstream of the
dam. The summary of conclusions is
summarized below:
1. Increasing the core side slopes in the vertical
cases reduced the factor of safety of both
upstream and downstream slopes. The
reduction was more significant in the steady
state case since the core material had lower
shear strength than the shell material. Also,
a significant pore water pressure developed
in the core caused this reduction.
2. Providing a slanting core had an
insignificant effect on the downstream slope
stability during the steady state and end of
construction; however, it influenced the
upstream slope during rapid drawdown and
the end of construction conditions.
3. The core side slopes can be increased up to
0.8H: 1V because it had an insignificant
effect on the slope stability.
4. The downstream stability reduced during
the steady state as the core top width
increased.
5. The slanting core shape had advantages over
the vertical core since the factor of safety
remained constant in the steady state
condition by increasing the core material
area.
REFERENCES
[1] Zedan AJ, Faris MR, Bdaiwi AK.
Performance Assessment of Shirin
Earth Dam in Iraq under Various
Operational Conditions. Tikrit
Journal of Engineering Sciences 2022;
29(2):61-74.
[2] USBR U. Department of the Interior,
Bureau of Reclamation (1987). Design of
Small Dams.
0
0.5
1
1.5
2
2.5
1357911 13
FOS (Steady State)
Core Side Slopes (cases)
Inclined
Core
Vertical
Core
Yaseen W. Aziz, Arkan H. Ibrahim, Osama K. MohammedAmin / Tikrit Journal of Engineering Sciences 2023; 30(2): 41-45.
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