Ijciet 10 01_067

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International Journal of Civil Engineering and Technology (IJCIET)
Volume 10, Issue 01, January 2019, pp. 735–745, Article ID: IJCIET_10_01_067
Available online at http://www.iaeme.com/ijciet/issues.asp?JType=IJCIET&VType=10&IType=1
ISSN Print: 0976-6308 and ISSN Online: 0976-6316
©IAEME Publication Scopus Indexed
EFFECT OF RAPID DRAWDOWN WATER IN
UPSTREAM AL-WAND DAM BY USING
GOE-STUDIO SOFTWARE
Weam Abdulwahhab Mohammed
Assistant Lecturer, M.Sc, In Environmental Engineering Management and Technology,
Ministry of Education, Babylon, Iraq
Mustafa Hussein Abed AL-Dulaimi
Assistant Lecture, M.Sc, In Water Resources Engineering, Ministry of Education,
Hilla, Babylon, Iraq
Thair Jabbar Mizhir Alfatlawi
Assistant Professor, Doctor in civil Engineering Department, University of Babylon,
Hilla, Babylon, P.O.B. 4, Iraq
ABSTRACT
The rapid drawdown effects directly on the stability of upstream slope of earth
dams, where the seepage direction will be in the reverse direction due to emergency
emptiness, which causes flow from downstream to upstream through the dam body,
such flow may be not considered in design. In this research two cases of rapid
drawdown are adopted, in the first case, the reservoir is empty from service canal
(outlet flow) where the discharge of this canal is 200 m3
/sec. In the second case, the
reservoir is empty by spillway canal with discharge capacity equal to 2750 m3/sec.
The results show that the discharge from spillway takes a few hours which threaten
the dam stability compering with allowable factor of safety while discharge from
outlet flow service takes a few days and the threaten was nominal, both of them under
rapid drawdown condition .
Key words: AL-Wand Dam, rapid drawdown, stability, Goe-studio, earth dam, factor
of safety, finite element
Cite this Article: Weam Abdulwahhab Mohammed, Mustafa Hussein Abed AL-
Dulaimi and Thair Jabbar Mizhir Alfatlawi, Effect of Rapid Drawdown Water in
Upstream Al-Wand Dam by Using Goe-Studio Software, International Journal of
Civil Engineering and Technology (IJCIET) 10(1), 2019, pp. 735–745.
http://www.iaeme.com/IJCIET/issues.asp?JType=IJCIET&VType=10&IType=1

Effect of Rapid Drawdown Water in Upstream Al-Wand Dam by Using Goe-Studio Software
1. INTRODUCTION
The stability is very important factor during the operating work of dams. Sometime, it needed
to reduce water level rapidly upstream the earth dam when natural disaster or the emergence
of a defect that threatens the body of the dam and stability. Dams are emptied to
accommodate floodwaters or when large quantities of water are needed for agriculture in the
dry season. The analysis of the stability of the upstream during the rapid drawdown condition
is important, this drawdown may be partially or completely (Alonso Pérez de Agreda &
Pinyol Puigmartí, 2009). Since pore water pressure inside soil at the upstream shell remains
high for a period of time (Fredlund et al., 2011) and (Tran, 2004), this pressure greatly affects
the stability of the dam when it decreases and is associated with the properties of mechanical
and physical soil (Nian et al., 2011) and (Narita, 2000). The soil with low permeability
requires a long period of time to get out of the water pores, while the soil with high
permeability requires a shorter time (Xinting & Zhenhua, 2016) and (Army, 2003). In this
study, the rapid drawdown of the AL-WAND dam is examined considering the hydraulic
properties of the dam body (reduction amount - drawdown time) using geo-studio 2012
software both (SEEP/W and SLOPE/W) programs as a package of finite element
method(Hassan &K.N.Kadhim, 2018). The computed factors of safety one compared with the
factors of safety values shown in the table (1).
Table 1 Allowable factor of safety in earth dam (state of Colorado department of natural resources
2007)
Upstream
Fullness case (Steady state) 1.3 -1.5
Drawdown case (Transient ) 1.2-1.3
Downstream
Fullness case (Steady state) 1.5
Earth quick case 1.2
2. MATHEMATICAL MODEL FOR SEEP STUDY
Darcy law was applied to study seepage in saturated and unsaturated soil:
(1)
Where:
q= discharge unit; L2
/T.
k= hydraulic conductivity; L/T.
i= hydraulic gradient; dimensionless.
Hydraulic conductivity takes a variable value, changes with volumetric water content and
total head as:
( ) ( ) (2)
Where:
H= total head; L.
kx= hydraulic conductivity with x-axis; L2
/T.
ky= hydraulic conductivity with y-axis ; L2
/T.
Q= total discharge (source); L3
/T.
θ= volumetric water content; L3
.
t= time; T.
In steady state seepage, the equation becomes:

Weam Abdulwahhab Mohammed, Mustafa Hussein Abed AL-Dulaimi and
( ) ( ) (3)
The changes in volumetric content of water related to the state of stress and soil
characteristics. As the law of stress for both cases in saturated and unsaturated soil was related
to the pressure of the air in the pores and pressure absorption as equation below:
(4)
Where:
mw= slope of saturation curve as shown in Figure 1. The total head calculated from the
relation
Figure 1 Saturation curve
(5)
Where:
Uw= pore water pressure; F/ L2
.
γw= weight density of water; F/ L3
.
= water depth for point studied; L.
Equation (5) can be written as:
( ) (6)
After substituting in equation (4):
( ) (7)
Then substituting in general equation (2) to get the:
( ) ( )
( )
(8)
Considering y is constant with time the equation become:
( ) ( ) (9)
Solve this integral equation by numerical methods (F.E.M) in the GEO-STUDIO software
to find the results of seepage analysis in steady and unsteady state.
The equilibrium theory was used to calculate the factor of safety, which determined from
the principle that shear force is generated in the soil mass, should be less than the soil
resistance to shear on the entire length of the sliding surface [10].
For analysis effective stress, the shear force is determined from the following equation:
( ) (10)
Where:

= shear force; F.
= cohesion force; F.
= friction angle; dimensionless.
= summation of stress; F/L2
.
3. AREA DESCRIPTION
As shown in Figures 2 and 3 AL-Wand dam is located on AL-Wand river at 3km south-east
Khanakeen in Diyala city and 6km from Iran-Iraq border at coordinates 34°20′00″N-
45°23′00″. Al-Wand dam is an earth with a clay core, the length of this dam is 2.8km and the
reservoir area with (normal or minimum) water level is 3204km2
. . Table 2 lists the material
properties of AL-WAND dam.
Figure 2 AL-WAND Dam Location. Figure 3 Coordinates AL-Wand dam.
Table 2 Material properties of AL-WAND Dam.
Material Permeability
(L/T)
γ
(KN/L3
)
C
(kN/L3
)
Φ
(degree)
Shell 0.001 18 0 25
Core 4.8*10-19
18 210 10
Fine filter 0.07 18 0 30
Coarse filter 0.11 18 0 30
Upper layer 8*10-5
20 30 30
Lower layer 3*10-6
23 100 36
4. RESULTS AND DISCUSSION
4.1. Seepage analysis
Geo-studio is used as a package (SEEP/W and SLOPE/W) for analyzing the seepage and
stability according to F.E.M in two dimensions to discuss steady and unsteady seepage state.
The water level in the upstream is 601m, and the bottom level of the lake is 566m, which
means that the upstream shell subject to 35m water head and There is no water in the back of
dam. Different scenarios of rapid discharge cases are studied to determine the effect of water
drop from level 601m to 581m, which mean the drawdown head is 20m. Figure 4 represents
typical cross section of AL- Wand dam which showing its components and water elevation.
The water amount removal from dam lake when water level drawdown 20m is 123428571m3
.
In this research two cases of rapid drawdown are adopted, in the first case, the reservoir is

empty from service canal (outlet flow) where the discharge of this canal is 200 m3
/sec. In the
second case, the reservoir is empty by spillway canal with discharge capacity equal to 2750
m3/sec. therefore; the time required for first case is 7 days and 12 hours for second case.
Figure 5 and Figure 6 show the phreatic line and total head distribution within a dam body at
steady state condition with zero time, where the water level is 601m as in Figure 5 and 581m
as in Figure 6. Figure 7 to Figure 9 show the phreatic line and total head distribution when
using service canal with time dependent. Figure 10 to Figure 11 show the phreatic line and
total head distribution when using spillway canal with time dependent. For two scenarios, the
pore water pressure increases in upstream shell region with the time increases, for this reason
the total head increasing with time, therefore the phreatic line shape and total head
distribution is changed as shown in Figures 5 to 11.
Figure 4 Al-Wand dam with the material details
Figure 5 The phreatic line and total head distribution for steady state condition with zero time
(water level is 601m).
Figure 6 The phreatic line and total head distribution for steady state condition with zero time
(water level is 581m).
Lower layer
Upper layer Upper layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
601 m
566 m
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
601 m
566 m
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
6
14
601 m
566 m
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40

Figure 7 The phreatic line and total head distribution when using service canal at time (2) day.
Figure 10 The phreatic line and total head distribution when using spillway canal at time (7.2)
hours.
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
566 m
601 m
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
566 m
601 m
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
566 m
601 m
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
601 m
566 m
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40

Figure 11 The phreatic line and total head distribution when using spillway canal at time (12) hours.
4.2. Stability Analysis
The upstream shell stability is studied, which is most affected by rapid drawdown, using
GEO-STUDIO (slope/w). Different methods of analysis are used for analysis and for factor of
safety calculation such as ( Bishop, ordinary and janbu) (morgensterm – price) and (spencer)
…etc. water head distribution results determined by (seep/w) for both steady state and rapid
drawdown cases are used later for slope stability analysis by (slope/w). Morgensterm - price is
adopted as analysis procedure to calculate the factor of safety against sliding that which
considered the force equilibrium and momentum. The factor of safety against sliding for
steady state condition with zero time and 601m water level in upstream dam is (1.335) as
shown in Figure 12, this factor of safety satisfied the specification that determine the value
between (1.3 -1.5) for fullness case (steady state). Figure 13 shows the factor of safety against
sliding for steady state condition with zero time and 581m water level in upstream dam, the
factor of safety for this case also between specific limit where its (1.35). To analyze the
resistance of the upstream slope with time at rapid drawdown. For selected cases, the amount
of water that reduces the water level from 601m to 581 m will be discharged in two times (7
and 0.5) day according to discharged location as shown in Figure 14. Figure 15 to 17 show
the factor of safety calculations when service canal used for dam reservoir emptiness while
Figure 18 to Figure 19 shows that when spillway canal used for emptiness. The factor of
safety for the two steadied cases, it can be seen that the factor of safety against sliding
decreases with the decreases of empting time. On the other hand, the factor of safety
decreases with the increases of drawdown time because rapid drawdown applies high
hydraulic gradient within dam body which leads to increases pore water pressure and reduce
upstream slope resistance. The factor of safety against sliding through rapid drawdown is not
within specification that may cusses dams failure if it.
Figure 12 Factor of safety against sliding for steady state condition with zero time (water level is
601m).
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
601 m
566 m
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
1.335
566 m
601 m
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
F.S. =

Figure 13 Factor of safety against sliding for steady state condition with zero time (water level is
581m).
Emptying from service canal Emptying from spillway canal
Figure 14 Selected time for analysis by location of emptying.
Figure 15 Factor of safety against sliding when using service canal at time (2) day.
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
6
14
1.350
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
New Function
TotalHead(m)
Time (days)
15
20
25
30
35
0 1 2 3 4 5 6 7
New Function (2)
TotalHead(m)
Time (days)
15
20
25
30
35
0 0.1 0.2 0.3 0.4 0.5
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
0.989
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
F.S. =
F.S. =

Figure 16 Factor of safety against sliding when using service canal at time (5) day.
Figure 17 Factor of safety against sliding when using service canal at time (7) day
Figure 18 Factor of safety against sliding when using spillway canal at (7.2) hours.
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
0.893
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
0.864
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
0.634
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
F.S. =
F.S. =
F.S. =

Figure 19 Factor of safety against sliding when using spillway canal at (12) hours.
Emptying from service canal Emptying from spillway canal
Figure 20 Factor of safety against sliding with time.
6. CONCLUSIONS
 The factor of safety against sliding decrease with increasing time at fixed velocity of water
drawdown as shown in (Fig. 20).
 The factor of safety against sliding decrease with decreasing time of water drawdown.
 The rapid drawdown from spillway canal more dangerous than utilization service canal.
 The factor of safety against sliding is outside specific limit.
REFERENCES
[1] Alonso Pérez de Agreda, E. and N. M. Pinyol Puigmartí, Slope stability under rapid
drawdown conditions. in Proceedings of the First Italian Workshop on Landslides, 2009,
p. 11-27.
[2] Army, U., 2003: Engineering Manual. Engineering and design-Slope stability. US Army
corps of engineering.
[3] Hassan and Kadhim Naief Kadhim (Development an Equation for Flow over Weirs Using
MNLR and CFD Simulation Approaches). (IJCIET), Volume 9, Issue 3, (Feb 2018)
Lower layer
cutoff
shell
fine filter
core
fine filter
coarse filter shell
shell
34
6
14
0.521
Distance
0 20 40 60 80 100 120 140 160 180 200 220 240 260 280
Elevation
-60
-50
-40
-30
-20
-10
0
10
20
30
40
Factor of Safety vs. Time
FactorofSafety
T ime (days)
0.85
0.9
0.95
1
1.05
1.1
1 2 3 4 5 6 7
Factor of Safety vs. Time
FactorofSafety
T ime (hr)
0.5
0.55
0.6
0.65
0.7
0.75
0.8
0.85
2 4 6 8 10 12
F.S. =

[4] Fredlund, M., H. Lu and T. Feng, 2011: Combined seepage and slope stability analysis of
rapid drawdown scenarios for levee design. Geo-Frontiers 2011: Advances in
Geotechnical Engineering.
[5] Narita, K., 2000: Design and construction of embankment dams. Dept. of Civil Eng., Aichi
Institute of Technology.
[6] Nian, T., J. Jiang, S. Wan and M. Luan, 2011: Strength Reduction FE analysis of the
stability of bank slopes subjected to transient unsaturated seepage. Electronic Journal of
Geotechnical Engineering, 16.
[7] Tran, T. X., 2004: Stability problems of an earthfill dam in rapid drawdown condition.
Grant Project, 02.
[8] Xinting, L. and Z. Zhenhua, 2016: Stability of Bank Slope Under Reservoir Water
Drawdown. Physical and Numerical Simulation of Geotechnical Engineering, 33.
[9] Stability Modeling with GEO-SLOPE 2012 Version software.
[10] State of Colorado department of Natural Resources,Rules and Regulations for Dam Safety
and Dam Construction. Colorado, 2007,76
[11] Seepage Modeling with GEO-SLOPE 2012 Version software.

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