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Geotechnical implications of subsurface water rise in Kuwait
Engineering Geology 31 (1991) 59-69 Elsevier Science Publishers B.V., Amsterdam
59
Geotechnical implications of subsurface water rise in Kuwait H.A. A l - S a n a d a a n d F . M . S h a q o u r b • Civil Engineering Department, Kuwait University, P.O. Box 5969, 13060 Safat, Kuwait bGeology Department, Kuwait University, P.O. Box 5969, 103060 Safat, Kuwait
(Received August 31, 1989; accepted after second revision July 7, 1990)
AI-Sanad, H.A. and Shaqour, F.M., 1991. Geotechnical implications of subsurface water rise in Kuwait. Eng. Geol., 31: 59-69. There is evidence that groundwater is rising under Kuwait City. This paper discusses the causes and geotechnical implications of such a rise. An explanatory model for the problem of rising groundwater, including the contributing parameters is introduced. Downward percolation from subsurface pipe networks and from excess irrigation, together with the local geologic conditions, form the main source of the problem. Potential geotechnical problems are presented based on reviewedand conducted laboratory and field tests. Reduction in shear strength of the cemented soil type due to saturation is evident.
INTRODUCTION The State of Kuwait forms part of the Arabian desert which is characterized by arid climatic conditions with extremely high temperatures and evaporation rates. The area was rapidly inhabited and urbanized after the discovery of oil in 1946. During the last few years, the water level has risen in a remarkable way in some residential areas of Kuwait City and the suburbs. As a result, water has percolated into basements of some houses, causing structural, geotechnical and environmental problems. The increase in the number and severity of reported floodings of previously dry basements has prompted research projects to study the geotechnical, geological and hydrological aspects of the problem. A major initiative in this direction was taken in 1985 by The Ministry of Electricity and Water (MEW), which granted the Kuwait Institute for Scientific Research (KISR) $3.5 million to study the problem of rising ground water (Kuwait Institute for Scientific Research, 1987). Again, in 1989, M E W asked K I S R to design and supervise construction of a pilot groundwater drainage system. In Kuwait University (KU), the authors completed a 2-year study of the geotechnical effects of fluctuation of the ground water table (AI-Sanad and Shaqour, 1987) and are now involved in a second project to study the effect of rising groundwater by using a model box to simulate field conditions. Finally, in 1990, the Kuwait Municipality started writing specifications and a code of practice for construction of basements and waterproofing. 0013-7952/91/$03.50
© 1991 Elsevier Science Publishers B.V. All rights reserved
60
AL-SANAD AND SHAQUOR
The purpose of the present article is to provide an overview of the problem, explaining the reasons for the rise in groundwater and flooding into basements, and to highlight potential geotechnical problems associated with this rise. SUBSURFACE CONDITIONS The subsurface soils in Kuwait are essentially calcareous, medium dense to dense, and primarily granular with discontinuous horizons of cemented, silty sands. The interbedding is somewhat random and it is difficult to separate discrete strata. The cemented zones of sand and silty sands are cemented with carbonates, sulphates and, locally, chlorides, resulting from the evaporation of shallow and saline groundwater. These soils, known locally as Gatch deposits, are generally characterized by low permeabilities which may result in the formation of hard pans that arrest perched groundwater. The groundwater table under Kuwait city is shallow and ranges in depth from about 1.0m near the coast to about 30.0m landwards (Fig.l). The water table generally parallels the surface topography, which gently slopes from inland towards the coast. Groundwater conditions in the residential area are complex; from available records they do not conform to any sharply recognisable pattern (Fig.l). This may be the local result of recharges caused by faulty water mains and sewers, and excessive irrigation. In order to investigate the seasonal and tidal fluctuation of groundwater, its depth was monitored in stand pipes placed in various locations in Kuwait City and the suburbs as indicated in Fig.2. Measurements of water depths in standpipes 1-12 in
Fig.1. Contours of depth to water table (modifiedfrom Kuwait Institute of ScientificResearch, 1987).
61
SUBSURFACE WATER RISE IN KUWAIT
• R.R
KUWAIT
A zljL UN
Stand pipe Ring Roads
~--~
ARABIAN
KUWAIT B A Y ~
5thF Fig.2.
Map to show the locations of the standpipes used in this study.
June and October showed a maximum seasonal difference of 28 cm. Continuous observations for 1 month of standpipes 13-16 indicated a maximum variation of 12 cm. A maximum tidal variation of 8 cm was indicated from hourly readings in standpipes 17 and 18. These tidal changes are probably associated with the nearby sea tides. The insignificance of the water level response to tidal fluctuations was also confirmed by the KISR study (1987), as shown in Fig.3. From experience, the authors believe that in the green areas the water level rises several centimeters in the summer. This is the result of excess irrigation in the hot summer season, when brackish irrigation water is provided to dwellings for an annual fixed rate of $15, regardless of the quantity used. The general trend of rising t,,.
3
0
-
~ 1.9| 2.02"0 /
l'-"':
.~.
,t..
t .
. . t
E "'
•
I
.L
0
2
6
,
.t,
6
!~ I0 12 I~ 16 m 70 22 2~
. I
,
,
.L
Time
(h)
Well
No. (Fig. l )
,
I ' I K ' I 2.$ k m
| is5 es~ o
O.O& km U,.6. E6
i
!
i
LEGENO
2.32.
RM- 2A
o !!li!RM-2A J~
O.6Okm
Q.
2:"."t
. . f ....
i..
f
.
.
. t . . ,
.
'- 6
e
IO I2 v. ~ le 20 22 2~. Time ( h )
o.10km
":r 2
. t..
0.60 km
Distoncefrom the coast
26.6.86
Date ot monito~incj
High
tide
Low
tide
Fig.3. Water level response to tidal fluctuation (modified from Kuwait Institute of Scientific Research, 1987).
62
AL-SANAD
AND SHAQUOR
water level in the newly developed suburbs and the repeated increase during the summer is illustrated in the hydrograph shown in Fig.4. The salinity of both soil and groundwater is variable, but generally high. Concentration of Total Dissolved Salts (TDS) of water samples taken from locations 4, 8 and I I was 28, 12 and 16 g/l, respectively. Chemical analysis of 52 soil samples from locations 1-12 has shown that maximum chloride and sulphate contents were 7000 ppm and 7800 ppm, with an average concentration of 1000 ppm and 1400 ppm respectively. Analysis of 29 water samples resulted in maximum chloride and sulphate contents of 10352 ppm and 6350 ppm, with an average concentration of 5000 ppm and 4000 ppm, respectively. These high concentrations indicate the need for protection of concrete and reinforcement. P H E N O M E N O N OF THE RISE IN SUBSURFACE WATER LEVEL
A rising ground water table is a major problem in many cities of the World (Paal, 1984; Abu-Rizaiza et al., 1985; Wilkinson, 1985). The rise in Kuwait City and the suburbs varies, depending on topography, subsurface soils, and intensity and character of urbanization. The rise in water level is recognized: (I) through the records of water level readings from standpipes installed and monitored since 1985 by the MEW (Kuwait Institute of Scientific Research, 1987) in locations of Kuwait City and the suburbs (Figs.I and 4); (2) through the increase in reported flooding of previously dry basements. Although most of these basements were constructed in dry soils and without any waterproofing, they remained dry for many years. In Kuwait, which is considered semi-arid, evaporation exceeds precipitation (less than 200 mm annual precipitation). The difference is normally compensated for by groundwater flow from the southwest towards the northeast, but this natural equilibrium is being disrupted by urbanization. In general, intensive urban development has vastly reduced evaporation by covering open ground with structures and pavements. These developments have also increased infiltration of water into the subsurface through excess irrigation and leakage from sewers, water mains and septic tanks. The rise in groundwater level is also aggravated by the damming effect of construction extending below the water table. The contributions of these diffeent factors is illustrated in Fig.5 and Table I. Well
No
. MF-
1A
8 60 o
B 50
E 8 40 • 8 30 2 ~, 820 8 10
l M
[
I I I i I ] I I [ ] I I I I I I I J A S O N O J F M A M J J A S O N D J F M A M 1985
1966
i
I
1
I
1
1987
Fig.4. Well hydrograph showing changes in water level in suburban areas (from Kuwait Institute of Scientific Research, 1987).
SUBSURFACE
_ _
WATER
,,
~:~.~:~:.~.~.%..,--:.._...:.:.. • .:...; .
...?..o:= •
"V
•
"
'
. '
"
63
RISE IN KUWAIT
"' '-
.
.
.
..
.
.
. . . . : z r • .v. ...
'
- .'
"V
.'" '
•
V
.
~
• -rr .
.
. . , ~ ~
-.:.....-:...;.:.;.::..?~....:...:...:....?-....::.......:....
..
:
"
v
.
-..
•
---v-r
"
" "
v"
." ¥
~
".
'
v
."
•
.
•
:=:" ,.
" .
•
Conceptual
model
for
groundwater
level
rise
•
'..
:.'"
L i Nm'malgroundwaterlevel. • ) wate¢. D I~iS4KIgrou~lv~er level. ( Infiltrated (~ r,t.w/ar.erunoff. [ ] Sewer line. (~ Septic tank. Le~IIy sewage. Fig.5.
".==..
, - ) . y ;
"
'. .
~:
.
:.
:rr'. " ¥
'-i .
...
".... ".'
•
. "
.
.....
•
."
". V..' -, : .
.
--rr
.V
" .... ".-
. v
o
• "
" ,.,
•
Loosesand (hlghly perrmNIbie ) Gath l a y e r tseml-l~rm@abl@toIn~l~rn*~.
in Kuwait.
The relatively impermeable nature of the surface and near-surface gatch deposits in Kuwait has resulted in the localized rise or perching of subsurface water. Part of this water may migrate laterally, where the gradient allows, until it intrudes into improperly waterproofed basements. This is indicated by basement flooding as a result of adjacent irrigation or broken pipes. The other part of this woter either evaporates or slowly infiltrates the semi-hard pan until it joins normal ground water. Continuous supply of water is expected to cause a general rise in the groundwater table leading to permanent flooding of basements. Additionally, when an excavation is made for the construction of basements in the gatch deposits, any backfill is usually either granular material of greater permeability or the original soil, which now has a greater permeability because of improper recompaction. This results in "ponding" of infiltrating water, which will eventually finds its way into the improperly waterproofed basements. Chemical analysis of some samples of water from the flooded basements indicates pronounced dilution (lower salinity) from normal groundwater (Table 2) with higher values of nitrogen. This suggests that it is contaminated with sewage and/or irrigation water. THE
EFFECT
OF
RISING
WATER
TABLE
ON
GEOTECHNICAL
DESIGN
The voids between the soil particles may contain either or both air and water. Depending on the void content, the soil may be described as dry, saturated or partially saturated. The natural moisture content in Kuwait ranges between 0 and 25%, and saturation ranges between 0 and 100%.
64
AL-SANAD AND SHAQUOR
TABLE I Recharge and discharge balance of Kuwait City and Suburbs for 1985 (Kuwait Institute for Scientific Research, 1987) Water balance components
I000 m3 d- t
Gross total recharge
(%) Recharge Natural recharge Lateral inflow Upward leakage Natural recharge subtotal
7.4 2.3 9.7
10.5 3.3 13.8
26. I 13.2 12.2 8.9 60.4
37.3 18.8 17.4 12.7 86.2
Total recharge
70.1
100.0
Discharge Natural discharge Lateral outflow Downward leakage Evapotranspiration loss Natural discharge subtotal
17.0 11. I 11.6 39.7
24.3 15.8 16.5 56.6
20.3
29.0
Total discharge
60.0
85.6
Net change in storage (Total recharge - total discharge)
I 0.1
14.4
Man-made recharge Septic tank Irrigation Sewerage network loss Water distribution system loss Man-made recharge subtotal
Discharge through man-made facilities (storm drainage and sewage network)
The presence and movements of water in the soil can affect most designs. Therefore, reliable information regarding the level of the groundwater is essential. Changes in groundwater level from tidal and seasonal variations have been shown to be less than 28 cm, and thus may have little effect on conventional structures. However, because of its magnitude the general rise in the water table in Kuwait City and its suburbs has to be considered. It is estimated that the groundwater level in the older suburbs of Kuwait City has risen from one to two meters in the past thirty years. A future rise in the groundwater level in the newly developed areas is expected to be significant, and must be considered during design. The important geotechnical impacts of a rising subsurface water level may be summarized as follows: (!) Flooding of improperly waterproofed basements.
SUBSURFACE WATER RISE IN KUWAIT
65
TABLE 2 Chemical analysis of water in some of the flooded basements in Kuwait City compared to chemical composition of normal groundwater in the region Sample
TDS (ppm)
pH
Ca (ppm)
Sr Mg ( p p m ) (ppm)
Na (ppm)
K (ppm)
7.0 7.8 8.0 7.7 7.4 7.3 7.8 7.4 7.6 7.1 8.3 7.4 7.8 7.4 -
138 24 24 5 401 377 418 405 420 422 572 660 327 405 482 444 809 847
1.2 0.4 0.4 4.1 3.5 3.5 . 9.8 14.0 11.1 11.1 . 6.6 6.2 14.5 . .
14 14 15 17 36 29 88
. 108 147 121.7 57.2 . . 186 23 322 . . . .
450 168 186 291 209 285 330 . 734 756 737 769 . 769 510 1270 . .
354 955 960 378
. . 10.7
270 . . . . 384
1185 . . 5900
HCO3 SOa (ppm) (ppm)
CI (ppm)
NO3 (ppm)
116 122 122 232 122 183 342 488 159 212 146 120 620 244 555 396 976 1240
92 15 31 202 1246 1237 633 1408 1601 1513 2013 1967 1630 2505 1520 2650 2816 3171
341 54 59 29 538 538 886 I100 884 862 948 1250 1260 1038 920 1923 2201 2521
16 7 8 60 104 114 141 127 12 32 24 96 121 33 47 126 127 121
259 488 490 275
1670 2991 3000 6906
2382 3444 3500 7643
10 56 50 66
Kuwait City 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
435 480 512 650 195 1984 2336 2630 3120 3200 3264 3570 3360 3820 3840 5120 5760 6080
19 88 89 28 65 59 22 .
51 71 51.6 79 106 104 II1
Regwnal Groundwater 19 20 21 22
6400 7680 7700 14720
7.4 7.3 7.4 7.5
70
112
TDS = total dissolved solids. (2) D e v e l o p m e n t o f uplift pressure, which m u s t be resisted by the weight o f the building, drains, o r o t h e r means. (3) A high sulphate a n d c h l o r i d e c o n t e n t o f g r o u n d w a t e r m a y result in the d e t e r i o r a t i o n o f the c o n c r e t e o f f o u n d a t i o n s , b a s e m e n t walls an d buried structures. (4) In cr eas ed cost a n d associated technical p r o b l e m s r e q u i r e d by d e w a t e r i n g the site d u r i n g c o n s t r u c t i o n o f f o u n d a t i o n s a n d basements, an d a need for w a t e r p r o o f i n g . (5) R e d u c t i o n in effective stress as a c o n s e q u e n c e o f increased p o r e pressure, which results in the r e d u c t i o n o f the shear strength o f g r a n u l a r soils. It is also expected that shear strength p a r a m e t e r s are reduced w h e n a soil is submerged. Fig.6 shows the r e d u c t i o n in the friction angle ( ¢ ) a n d c o h e s i o n (c) as a result o f s u b m e r g e n c e ( A I - S a n a d et al., 1989). T h i s strength r e d u c t i o n is also s h o w n by the reduced p e n e t r a t i o n resistance o f G a t c h (Fig.7) after s o a k i n g (A1-Sanad an d S h a q u o u r , 1987). (6) R e d u c t i o n in the b e a r in g capacity, quit is expressed in the f o l l o w i n g relationship (Das, 1985):
q~l, = ?No + :DNq + ~ N.~
66
AL-SANADAND SHAQUOR 300-
•-',
250-
Ut
200-
{
•
Dry
A
Soaked
Gatch Gatch
150.
S
o
sb lbO , ~ ~6o ~bo x N o r m a l Stress (KPa)
Fig.6. Direct shear test results for dry and soaked Gatch.
Penetration Resistance (MN/m2) 5 0 .
.
.
.
.
'
10 .
.
.
.
'
15 "
"
"
'
2o .
.
.
.
.
/4-
8'E
12.
~
.
~
16,
. 2L,. 2~
Fig.7. Penetration resistance of soaked and dried Gatch.
Where N,, Nq and Ny are bearing capacity factors. The reduction in c, ~ and the unit weight (~) of the soil results in a reduction in qu,. The extent of the reduction in bearing capacity will depend on the width of the foundation (B) and the position of the water level relative to the base of the foundation. (7) Increased lateral pressure on basement walls owing to increased hydrostatic pressure. (8) Settlement of buildings whose foundations are constructed on collapsible soils or structural fills (i.e., fill used as the foundation soil). The collapsible soils lose strength and compress under load when soaked. Settlement of a two-storey building, constructed on a non-collapsible soil, due to adjacent dewatertng is shown in Fig.8. The water level was lowered between 2 and 3 m; as a result, the maximum settlement was only 4 mm, most of which was recovered upon returning the water to its original level.
SUBSURFACE
WATER
M
A l
OO
67
RISE IN KUWAIT
M i
1986
J ]
DEWATERING 5TOPPED
J l
l
A
S
O
i
N
D
I 1987 J
i
D E W A T E R I N G DEWATERING RESUMED STOPPED
5 E
~2c IE
hi .J p-. W
m
3C
,~C
Fig.8. Settlement of a two-storey building due to adjacent dewatering (Ghazali Street, Kuwait). TI, T2 and T3 are measurement targets.
(9) Continuous flow of water, either as a result of pumping during construction, or as a result of pumping from sumps in basements infiltrated by water, may result in the washing out of fines or salts cementing the soil (AI-Bader, 1989). This, in turn, may cause reduction in strength and ultimately settlement or collapse. A summary of the factors contributing to the rise in groundwater level, and the geotechnical implications of this rise is presented in a conceptual form in Fig.9.
CONCLUSIONS
From the literature review and the information assembled in this article, the following can be concluded: (I) The rise in the water table in Kuwait City and the suburbs has been recognized, and the magnitude and distribution is being monitored in the MEW. (2) The rise in groundwater level has been evidenced by flooding of basements, uplift pressures, reduction in bearing capacity and soil strength, chemical attack and difficulties during construction. (3) The mechanism of the rise in subsurface water level has been discussed in the form of a model identifying the natural and manmade factors contributing to the rise. The model also illustrates the contribution of the Gatch to infiltration of water into basements with no or improper waterproofing. (4) The data collected regarding the tidal and seasonal variation of the groundwater level indicated a maximum variation of 28 cm.
ii
] Irrigation
j~L, psib~So~ I JConstructtonEk,l-J I°w ~ter I
J
t t
vailable Conditions
I
t
t
Septic Tanks
I
li
t
t
Damming Effect
t
I I
t
JEvaporation I
1 I
t
J Artificlal] t
Reduction
i I Soil Red"ction in I IConcrete IOeter~"~t~andof II I Hydrostatic Increased J Strength Basement Parameters ICo,os~ o~ I Pressure t Flooding of
Water and I Sower Mains I
]~'~'"'" i1~'--' I [
t
Fig.9. Model for the causes and effects of groundwater rise.
s,,~.ingSoil,
I ~.r~".OW.,.r I
[
I
High Evaporation
t
J
! I t IFo,mat~no'6atch
Saline Water
t
! Natural
t
I
,O C O
;> Z
> Z ;>
> r.~
SUBSURFACE WATER RISE IN KUWAIT
69
ACKNOWLEDGEMENTS
The writers would like to thank the Kuwait University research unit for the financial support of this research. The writers wish to thank the Ministry of Electricity and Water for granting permission to use the data in this study. REFERENCES Abu-Rizaiza, O.S., Atinbilek, H.Z., Sarikay, Khan, M.Z. and Baghdadi, A.N., 1985. Study of groundwater north and south of Jeddah. Final Rep. Water and Sewerage Dep., Jeddah, Saudi Arabia. AI-Bader, B.R., 1989. Leaching of a calcareous soil from Kuwait. MSc. Thesis, Civil Engineering Dep., Kuwait Univ., Kuwait. Al-Sanad, H.A. and Shaqour, F.M., 1987. Effect of groundwater level fluctuation on the engineering properties of desert sands. Final Rep. EV028, Kuwait Univ. Research Univ, Kuwait. AI-Sanad, H.A., Shaqour, F.M., Hencher, S.R. and Lumsden, A.L., 1989. The shear strength of saltcemented sand from Kuwait. Prec. Regional Conf. Civil Engineering, 1st (Bahrain). Das, B.M., 1985. Principles of Geotechnical Engineering. PWS, Boston, Mass., USA. Kuwait Institute for Scientific Research, 1987. Study of subsurface water rise in the Residential Areas of Kuwait. Final Rep. EE556, submitted to Min. Electricity and Water, Kuwait. Kuwait Municipality, 1983. Baloush Multi-storey Car Park Soil Investigation Report. Kuwait. Ministry of Public Works, 1981. Jahra/Gazali Motorway Soil Investigation Report, Kuwait. Paal, T., 1984. Change in ground water level--change of design parameters. In: Prec. Conf. Soil Mechanics and Foundation Engineering, 6th (Budapest), pp. 229-236. Pan Arab Consulting Engineers, 1986. Arab Organizations Headquarters Soil Investigation Rep., Kuwait. Wilkinson, W.B., 1985. Rising Groundwater Levels in London and Possible Effects on Engineering Structures. In: Prec. Congr. Int. Assoc. Hydrologists, 18th (Cambridge, UK).
59
Geotechnical implications of subsurface water rise in Kuwait H.A. A l - S a n a d a a n d F . M . S h a q o u r b • Civil Engineering Department, Kuwait University, P.O. Box 5969, 13060 Safat, Kuwait bGeology Department, Kuwait University, P.O. Box 5969, 103060 Safat, Kuwait
(Received August 31, 1989; accepted after second revision July 7, 1990)
AI-Sanad, H.A. and Shaqour, F.M., 1991. Geotechnical implications of subsurface water rise in Kuwait. Eng. Geol., 31: 59-69. There is evidence that groundwater is rising under Kuwait City. This paper discusses the causes and geotechnical implications of such a rise. An explanatory model for the problem of rising groundwater, including the contributing parameters is introduced. Downward percolation from subsurface pipe networks and from excess irrigation, together with the local geologic conditions, form the main source of the problem. Potential geotechnical problems are presented based on reviewedand conducted laboratory and field tests. Reduction in shear strength of the cemented soil type due to saturation is evident.
INTRODUCTION The State of Kuwait forms part of the Arabian desert which is characterized by arid climatic conditions with extremely high temperatures and evaporation rates. The area was rapidly inhabited and urbanized after the discovery of oil in 1946. During the last few years, the water level has risen in a remarkable way in some residential areas of Kuwait City and the suburbs. As a result, water has percolated into basements of some houses, causing structural, geotechnical and environmental problems. The increase in the number and severity of reported floodings of previously dry basements has prompted research projects to study the geotechnical, geological and hydrological aspects of the problem. A major initiative in this direction was taken in 1985 by The Ministry of Electricity and Water (MEW), which granted the Kuwait Institute for Scientific Research (KISR) $3.5 million to study the problem of rising ground water (Kuwait Institute for Scientific Research, 1987). Again, in 1989, M E W asked K I S R to design and supervise construction of a pilot groundwater drainage system. In Kuwait University (KU), the authors completed a 2-year study of the geotechnical effects of fluctuation of the ground water table (AI-Sanad and Shaqour, 1987) and are now involved in a second project to study the effect of rising groundwater by using a model box to simulate field conditions. Finally, in 1990, the Kuwait Municipality started writing specifications and a code of practice for construction of basements and waterproofing. 0013-7952/91/$03.50
© 1991 Elsevier Science Publishers B.V. All rights reserved
60
AL-SANAD AND SHAQUOR
The purpose of the present article is to provide an overview of the problem, explaining the reasons for the rise in groundwater and flooding into basements, and to highlight potential geotechnical problems associated with this rise. SUBSURFACE CONDITIONS The subsurface soils in Kuwait are essentially calcareous, medium dense to dense, and primarily granular with discontinuous horizons of cemented, silty sands. The interbedding is somewhat random and it is difficult to separate discrete strata. The cemented zones of sand and silty sands are cemented with carbonates, sulphates and, locally, chlorides, resulting from the evaporation of shallow and saline groundwater. These soils, known locally as Gatch deposits, are generally characterized by low permeabilities which may result in the formation of hard pans that arrest perched groundwater. The groundwater table under Kuwait city is shallow and ranges in depth from about 1.0m near the coast to about 30.0m landwards (Fig.l). The water table generally parallels the surface topography, which gently slopes from inland towards the coast. Groundwater conditions in the residential area are complex; from available records they do not conform to any sharply recognisable pattern (Fig.l). This may be the local result of recharges caused by faulty water mains and sewers, and excessive irrigation. In order to investigate the seasonal and tidal fluctuation of groundwater, its depth was monitored in stand pipes placed in various locations in Kuwait City and the suburbs as indicated in Fig.2. Measurements of water depths in standpipes 1-12 in
Fig.1. Contours of depth to water table (modifiedfrom Kuwait Institute of ScientificResearch, 1987).
61
SUBSURFACE WATER RISE IN KUWAIT
• R.R
KUWAIT
A zljL UN
Stand pipe Ring Roads
~--~
ARABIAN
KUWAIT B A Y ~
5thF Fig.2.
Map to show the locations of the standpipes used in this study.
June and October showed a maximum seasonal difference of 28 cm. Continuous observations for 1 month of standpipes 13-16 indicated a maximum variation of 12 cm. A maximum tidal variation of 8 cm was indicated from hourly readings in standpipes 17 and 18. These tidal changes are probably associated with the nearby sea tides. The insignificance of the water level response to tidal fluctuations was also confirmed by the KISR study (1987), as shown in Fig.3. From experience, the authors believe that in the green areas the water level rises several centimeters in the summer. This is the result of excess irrigation in the hot summer season, when brackish irrigation water is provided to dwellings for an annual fixed rate of $15, regardless of the quantity used. The general trend of rising t,,.
3
0
-
~ 1.9| 2.02"0 /
l'-"':
.~.
,t..
t .
. . t
E "'
•
I
.L
0
2
6
,
.t,
6
!~ I0 12 I~ 16 m 70 22 2~
. I
,
,
.L
Time
(h)
Well
No. (Fig. l )
,
I ' I K ' I 2.$ k m
| is5 es~ o
O.O& km U,.6. E6
i
!
i
LEGENO
2.32.
RM- 2A
o !!li!RM-2A J~
O.6Okm
Q.
2:"."t
. . f ....
i..
f
.
.
. t . . ,
.
'- 6
e
IO I2 v. ~ le 20 22 2~. Time ( h )
o.10km
":r 2
. t..
0.60 km
Distoncefrom the coast
26.6.86
Date ot monito~incj
High
tide
Low
tide
Fig.3. Water level response to tidal fluctuation (modified from Kuwait Institute of Scientific Research, 1987).
62
AL-SANAD
AND SHAQUOR
water level in the newly developed suburbs and the repeated increase during the summer is illustrated in the hydrograph shown in Fig.4. The salinity of both soil and groundwater is variable, but generally high. Concentration of Total Dissolved Salts (TDS) of water samples taken from locations 4, 8 and I I was 28, 12 and 16 g/l, respectively. Chemical analysis of 52 soil samples from locations 1-12 has shown that maximum chloride and sulphate contents were 7000 ppm and 7800 ppm, with an average concentration of 1000 ppm and 1400 ppm respectively. Analysis of 29 water samples resulted in maximum chloride and sulphate contents of 10352 ppm and 6350 ppm, with an average concentration of 5000 ppm and 4000 ppm, respectively. These high concentrations indicate the need for protection of concrete and reinforcement. P H E N O M E N O N OF THE RISE IN SUBSURFACE WATER LEVEL
A rising ground water table is a major problem in many cities of the World (Paal, 1984; Abu-Rizaiza et al., 1985; Wilkinson, 1985). The rise in Kuwait City and the suburbs varies, depending on topography, subsurface soils, and intensity and character of urbanization. The rise in water level is recognized: (I) through the records of water level readings from standpipes installed and monitored since 1985 by the MEW (Kuwait Institute of Scientific Research, 1987) in locations of Kuwait City and the suburbs (Figs.I and 4); (2) through the increase in reported flooding of previously dry basements. Although most of these basements were constructed in dry soils and without any waterproofing, they remained dry for many years. In Kuwait, which is considered semi-arid, evaporation exceeds precipitation (less than 200 mm annual precipitation). The difference is normally compensated for by groundwater flow from the southwest towards the northeast, but this natural equilibrium is being disrupted by urbanization. In general, intensive urban development has vastly reduced evaporation by covering open ground with structures and pavements. These developments have also increased infiltration of water into the subsurface through excess irrigation and leakage from sewers, water mains and septic tanks. The rise in groundwater level is also aggravated by the damming effect of construction extending below the water table. The contributions of these diffeent factors is illustrated in Fig.5 and Table I. Well
No
. MF-
1A
8 60 o
B 50
E 8 40 • 8 30 2 ~, 820 8 10
l M
[
I I I i I ] I I [ ] I I I I I I I J A S O N O J F M A M J J A S O N D J F M A M 1985
1966
i
I
1
I
1
1987
Fig.4. Well hydrograph showing changes in water level in suburban areas (from Kuwait Institute of Scientific Research, 1987).
SUBSURFACE
_ _
WATER
,,
~:~.~:~:.~.~.%..,--:.._...:.:.. • .:...; .
...?..o:= •
"V
•
"
'
. '
"
63
RISE IN KUWAIT
"' '-
.
.
.
..
.
.
. . . . : z r • .v. ...
'
- .'
"V
.'" '
•
V
.
~
• -rr .
.
. . , ~ ~
-.:.....-:...;.:.;.::..?~....:...:...:....?-....::.......:....
..
:
"
v
.
-..
•
---v-r
"
" "
v"
." ¥
~
".
'
v
."
•
.
•
:=:" ,.
" .
•
Conceptual
model
for
groundwater
level
rise
•
'..
:.'"
L i Nm'malgroundwaterlevel. • ) wate¢. D I~iS4KIgrou~lv~er level. ( Infiltrated (~ r,t.w/ar.erunoff. [ ] Sewer line. (~ Septic tank. Le~IIy sewage. Fig.5.
".==..
, - ) . y ;
"
'. .
~:
.
:.
:rr'. " ¥
'-i .
...
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•
. "
.
.....
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."
". V..' -, : .
.
--rr
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. v
o
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•
Loosesand (hlghly perrmNIbie ) Gath l a y e r tseml-l~rm@abl@toIn~l~rn*~.
in Kuwait.
The relatively impermeable nature of the surface and near-surface gatch deposits in Kuwait has resulted in the localized rise or perching of subsurface water. Part of this water may migrate laterally, where the gradient allows, until it intrudes into improperly waterproofed basements. This is indicated by basement flooding as a result of adjacent irrigation or broken pipes. The other part of this woter either evaporates or slowly infiltrates the semi-hard pan until it joins normal ground water. Continuous supply of water is expected to cause a general rise in the groundwater table leading to permanent flooding of basements. Additionally, when an excavation is made for the construction of basements in the gatch deposits, any backfill is usually either granular material of greater permeability or the original soil, which now has a greater permeability because of improper recompaction. This results in "ponding" of infiltrating water, which will eventually finds its way into the improperly waterproofed basements. Chemical analysis of some samples of water from the flooded basements indicates pronounced dilution (lower salinity) from normal groundwater (Table 2) with higher values of nitrogen. This suggests that it is contaminated with sewage and/or irrigation water. THE
EFFECT
OF
RISING
WATER
TABLE
ON
GEOTECHNICAL
DESIGN
The voids between the soil particles may contain either or both air and water. Depending on the void content, the soil may be described as dry, saturated or partially saturated. The natural moisture content in Kuwait ranges between 0 and 25%, and saturation ranges between 0 and 100%.
64
AL-SANAD AND SHAQUOR
TABLE I Recharge and discharge balance of Kuwait City and Suburbs for 1985 (Kuwait Institute for Scientific Research, 1987) Water balance components
I000 m3 d- t
Gross total recharge
(%) Recharge Natural recharge Lateral inflow Upward leakage Natural recharge subtotal
7.4 2.3 9.7
10.5 3.3 13.8
26. I 13.2 12.2 8.9 60.4
37.3 18.8 17.4 12.7 86.2
Total recharge
70.1
100.0
Discharge Natural discharge Lateral outflow Downward leakage Evapotranspiration loss Natural discharge subtotal
17.0 11. I 11.6 39.7
24.3 15.8 16.5 56.6
20.3
29.0
Total discharge
60.0
85.6
Net change in storage (Total recharge - total discharge)
I 0.1
14.4
Man-made recharge Septic tank Irrigation Sewerage network loss Water distribution system loss Man-made recharge subtotal
Discharge through man-made facilities (storm drainage and sewage network)
The presence and movements of water in the soil can affect most designs. Therefore, reliable information regarding the level of the groundwater is essential. Changes in groundwater level from tidal and seasonal variations have been shown to be less than 28 cm, and thus may have little effect on conventional structures. However, because of its magnitude the general rise in the water table in Kuwait City and its suburbs has to be considered. It is estimated that the groundwater level in the older suburbs of Kuwait City has risen from one to two meters in the past thirty years. A future rise in the groundwater level in the newly developed areas is expected to be significant, and must be considered during design. The important geotechnical impacts of a rising subsurface water level may be summarized as follows: (!) Flooding of improperly waterproofed basements.
SUBSURFACE WATER RISE IN KUWAIT
65
TABLE 2 Chemical analysis of water in some of the flooded basements in Kuwait City compared to chemical composition of normal groundwater in the region Sample
TDS (ppm)
pH
Ca (ppm)
Sr Mg ( p p m ) (ppm)
Na (ppm)
K (ppm)
7.0 7.8 8.0 7.7 7.4 7.3 7.8 7.4 7.6 7.1 8.3 7.4 7.8 7.4 -
138 24 24 5 401 377 418 405 420 422 572 660 327 405 482 444 809 847
1.2 0.4 0.4 4.1 3.5 3.5 . 9.8 14.0 11.1 11.1 . 6.6 6.2 14.5 . .
14 14 15 17 36 29 88
. 108 147 121.7 57.2 . . 186 23 322 . . . .
450 168 186 291 209 285 330 . 734 756 737 769 . 769 510 1270 . .
354 955 960 378
. . 10.7
270 . . . . 384
1185 . . 5900
HCO3 SOa (ppm) (ppm)
CI (ppm)
NO3 (ppm)
116 122 122 232 122 183 342 488 159 212 146 120 620 244 555 396 976 1240
92 15 31 202 1246 1237 633 1408 1601 1513 2013 1967 1630 2505 1520 2650 2816 3171
341 54 59 29 538 538 886 I100 884 862 948 1250 1260 1038 920 1923 2201 2521
16 7 8 60 104 114 141 127 12 32 24 96 121 33 47 126 127 121
259 488 490 275
1670 2991 3000 6906
2382 3444 3500 7643
10 56 50 66
Kuwait City 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18
435 480 512 650 195 1984 2336 2630 3120 3200 3264 3570 3360 3820 3840 5120 5760 6080
19 88 89 28 65 59 22 .
51 71 51.6 79 106 104 II1
Regwnal Groundwater 19 20 21 22
6400 7680 7700 14720
7.4 7.3 7.4 7.5
70
112
TDS = total dissolved solids. (2) D e v e l o p m e n t o f uplift pressure, which m u s t be resisted by the weight o f the building, drains, o r o t h e r means. (3) A high sulphate a n d c h l o r i d e c o n t e n t o f g r o u n d w a t e r m a y result in the d e t e r i o r a t i o n o f the c o n c r e t e o f f o u n d a t i o n s , b a s e m e n t walls an d buried structures. (4) In cr eas ed cost a n d associated technical p r o b l e m s r e q u i r e d by d e w a t e r i n g the site d u r i n g c o n s t r u c t i o n o f f o u n d a t i o n s a n d basements, an d a need for w a t e r p r o o f i n g . (5) R e d u c t i o n in effective stress as a c o n s e q u e n c e o f increased p o r e pressure, which results in the r e d u c t i o n o f the shear strength o f g r a n u l a r soils. It is also expected that shear strength p a r a m e t e r s are reduced w h e n a soil is submerged. Fig.6 shows the r e d u c t i o n in the friction angle ( ¢ ) a n d c o h e s i o n (c) as a result o f s u b m e r g e n c e ( A I - S a n a d et al., 1989). T h i s strength r e d u c t i o n is also s h o w n by the reduced p e n e t r a t i o n resistance o f G a t c h (Fig.7) after s o a k i n g (A1-Sanad an d S h a q u o u r , 1987). (6) R e d u c t i o n in the b e a r in g capacity, quit is expressed in the f o l l o w i n g relationship (Das, 1985):
q~l, = ?No + :DNq + ~ N.~
66
AL-SANADAND SHAQUOR 300-
•-',
250-
Ut
200-
{
•
Dry
A
Soaked
Gatch Gatch
150.
S
o
sb lbO , ~ ~6o ~bo x N o r m a l Stress (KPa)
Fig.6. Direct shear test results for dry and soaked Gatch.
Penetration Resistance (MN/m2) 5 0 .
.
.
.
.
'
10 .
.
.
.
'
15 "
"
"
'
2o .
.
.
.
.
/4-
8'E
12.
~
.
~
16,
. 2L,. 2~
Fig.7. Penetration resistance of soaked and dried Gatch.
Where N,, Nq and Ny are bearing capacity factors. The reduction in c, ~ and the unit weight (~) of the soil results in a reduction in qu,. The extent of the reduction in bearing capacity will depend on the width of the foundation (B) and the position of the water level relative to the base of the foundation. (7) Increased lateral pressure on basement walls owing to increased hydrostatic pressure. (8) Settlement of buildings whose foundations are constructed on collapsible soils or structural fills (i.e., fill used as the foundation soil). The collapsible soils lose strength and compress under load when soaked. Settlement of a two-storey building, constructed on a non-collapsible soil, due to adjacent dewatertng is shown in Fig.8. The water level was lowered between 2 and 3 m; as a result, the maximum settlement was only 4 mm, most of which was recovered upon returning the water to its original level.
SUBSURFACE
WATER
M
A l
OO
67
RISE IN KUWAIT
M i
1986
J ]
DEWATERING 5TOPPED
J l
l
A
S
O
i
N
D
I 1987 J
i
D E W A T E R I N G DEWATERING RESUMED STOPPED
5 E
~2c IE
hi .J p-. W
m
3C
,~C
Fig.8. Settlement of a two-storey building due to adjacent dewatering (Ghazali Street, Kuwait). TI, T2 and T3 are measurement targets.
(9) Continuous flow of water, either as a result of pumping during construction, or as a result of pumping from sumps in basements infiltrated by water, may result in the washing out of fines or salts cementing the soil (AI-Bader, 1989). This, in turn, may cause reduction in strength and ultimately settlement or collapse. A summary of the factors contributing to the rise in groundwater level, and the geotechnical implications of this rise is presented in a conceptual form in Fig.9.
CONCLUSIONS
From the literature review and the information assembled in this article, the following can be concluded: (I) The rise in the water table in Kuwait City and the suburbs has been recognized, and the magnitude and distribution is being monitored in the MEW. (2) The rise in groundwater level has been evidenced by flooding of basements, uplift pressures, reduction in bearing capacity and soil strength, chemical attack and difficulties during construction. (3) The mechanism of the rise in subsurface water level has been discussed in the form of a model identifying the natural and manmade factors contributing to the rise. The model also illustrates the contribution of the Gatch to infiltration of water into basements with no or improper waterproofing. (4) The data collected regarding the tidal and seasonal variation of the groundwater level indicated a maximum variation of 28 cm.
ii
] Irrigation
j~L, psib~So~ I JConstructtonEk,l-J I°w ~ter I
J
t t
vailable Conditions
I
t
t
Septic Tanks
I
li
t
t
Damming Effect
t
I I
t
JEvaporation I
1 I
t
J Artificlal] t
Reduction
i I Soil Red"ction in I IConcrete IOeter~"~t~andof II I Hydrostatic Increased J Strength Basement Parameters ICo,os~ o~ I Pressure t Flooding of
Water and I Sower Mains I
]~'~'"'" i1~'--' I [
t
Fig.9. Model for the causes and effects of groundwater rise.
s,,~.ingSoil,
I ~.r~".OW.,.r I
[
I
High Evaporation
t
J
! I t IFo,mat~no'6atch
Saline Water
t
! Natural
t
I
,O C O
;> Z
> Z ;>
> r.~
SUBSURFACE WATER RISE IN KUWAIT
69
ACKNOWLEDGEMENTS
The writers would like to thank the Kuwait University research unit for the financial support of this research. The writers wish to thank the Ministry of Electricity and Water for granting permission to use the data in this study. REFERENCES Abu-Rizaiza, O.S., Atinbilek, H.Z., Sarikay, Khan, M.Z. and Baghdadi, A.N., 1985. Study of groundwater north and south of Jeddah. Final Rep. Water and Sewerage Dep., Jeddah, Saudi Arabia. AI-Bader, B.R., 1989. Leaching of a calcareous soil from Kuwait. MSc. Thesis, Civil Engineering Dep., Kuwait Univ., Kuwait. Al-Sanad, H.A. and Shaqour, F.M., 1987. Effect of groundwater level fluctuation on the engineering properties of desert sands. Final Rep. EV028, Kuwait Univ. Research Univ, Kuwait. AI-Sanad, H.A., Shaqour, F.M., Hencher, S.R. and Lumsden, A.L., 1989. The shear strength of saltcemented sand from Kuwait. Prec. Regional Conf. Civil Engineering, 1st (Bahrain). Das, B.M., 1985. Principles of Geotechnical Engineering. PWS, Boston, Mass., USA. Kuwait Institute for Scientific Research, 1987. Study of subsurface water rise in the Residential Areas of Kuwait. Final Rep. EE556, submitted to Min. Electricity and Water, Kuwait. Kuwait Municipality, 1983. Baloush Multi-storey Car Park Soil Investigation Report. Kuwait. Ministry of Public Works, 1981. Jahra/Gazali Motorway Soil Investigation Report, Kuwait. Paal, T., 1984. Change in ground water level--change of design parameters. In: Prec. Conf. Soil Mechanics and Foundation Engineering, 6th (Budapest), pp. 229-236. Pan Arab Consulting Engineers, 1986. Arab Organizations Headquarters Soil Investigation Rep., Kuwait. Wilkinson, W.B., 1985. Rising Groundwater Levels in London and Possible Effects on Engineering Structures. In: Prec. Congr. Int. Assoc. Hydrologists, 18th (Cambridge, UK).