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JKAU; Earth Sci., Vol. 20 No.1, pp: 141-166 (2009A.D./1430 A.H.)
141
Mineralogical and Chemical Compositions of Shallow Marine Clays, East of Cairo, Egypt: A Geotechnical
Perception
Ali M. A. Abd-Allah, Yehia H. Dawood
*
, Samir A. Awad and
Waleed A. Agila
Dept. Geology, Fac. Science, Ain Shams Univ., Cairo, Egypt *Fac. of Earth Sciences, King Abdulaziz Univ., Jeddah, KSA
Received: 6/2/2008 Accepted: 29/6/2008
Abstract. The Eocene and Miocene shallow marine clays compose several foundation beds in the new cities, east of Cairo, Egypt. Mineralogical and chemical compositions of these clays were examined using XRD, SEM, ICP-OES techniques. Geotechnical and physical characteristics were investigated according to the standards of ASTM (1994). The XRD and SEM analyses confirm that the major non-clay minerals are quartz, halite, feldspars, calcite and goethite whereas the clay minerals are Na montmorillonite and kaolinite. The chemical data suggest that the sources of Si in the analyzed samples are essentially sand and silt fractions, whereas Al is derived from the clay fraction. Fe, Mg and Na occur either as main constituents of smectite or as replacements for Al in the clay mineral structures. The substitution of Al by the divalent cations results in formation of a negative charge on the clay crystal lattice. This negative charge is mostly balanced by adsorption of monovalent cation such as Na+ and K+ from the groundwater and/or during the diagensis process. Mn exists mainly as MnO cement and partially at the expense of Fe and Mg. The cement materials include also Fe, Ca and Na salts. Cu, Zn and other heavy metals are mainly adsorbed on the surface of clay platelets. The clays of the study area range in swelling from low to very high; these might cause serious engineering problems on wetting at the foundation levels. Fe, Ca, Mn, Mg, Na, K, Cu, and Zn enhance the swelling potentiality when present as substitution for Al or adsorption on the clay minerals and reduce it when exist as components of the cement materials. Results facilitate the interpretation that the swelling potentiality is largely affected by the type of clay mineral, its percentage, chemical composition, structures and presence of both cement materials and fine sand cushions.
Abd-Allah et. al.
142
Introduction
The geotechnical behaviors of rocks such as swelling, slaking, fracturing,
and disintegration are very important factors that play significant roles in
civil engineering and mining operations. These behaviors can be assessed
by the measurement of geotechnical properties of the rock, which are
closely dependent on their mineralogy and alteration history after rock
formation. Geological processes such as weathering, diagenesis and
alteration affect the mineralogical composition of rocks and consequently
have close relation to the geotechnical properties. Argillaceous rock,
which constitutes the major part of soft rocks, frequently causes serious
engineering and geotechnical problems. The apparent geotechnical
problems in modern urban construction of soft clay are mainly due to its
low strength, low durability and high compressibility. In such
circumstances, cement is frequently used as an additive to improve the
strength, durability, volume stability and compressibility of in situ soft
clay soils (Bergado et al. 1996; Tatsuoka et al. 1997 and O’Rourke et al.
1998).
Despite much work and many literatures which have been published
in the subject, the effects of mineralogy and chemistry on geotechnical
properties of argillaceous rocks have not yet been elucidated in detail.
Parker (1973) in his study of the geotechnical properties of terrestrial
clay soil stated that although bulk chemistry and mineralogy may help to
define the overall range of values for shear strength, they do not
determine the small scale variation. Ohtsubo et al. (1995) in their study
of marine clays from Ariake Bay of Japan, found that smectite content is
the governing factor for the consistency limits and activity. They also
reported that the iron oxides content resulted from pyrite oxidation is the
predominant factor for the sensitivity and the overconsolidation ratio.
The overconsolidation characteristics are attributed to interparticle
cementation by these oxides. Boone and Lutenegger (2000) studied the
relation between the mineralogical and geotechnical characteristics of
recent soft lacustrine and marine sediments in Mexico, Canada, USA,
Norway and Italy. They indicated that the carbonates may play an
important role as cementing materials but they are not the sole cause of
the other geotechnical properties of the sediments. Dhakal (2001) found
that the slake durability and other geotechnical behaviors of argillaceous
Mineralogical and Chemical Compositions of Shallow Marine Clays 143
rocks are strongly influenced by mineralogy. Dananaj et al. (2005)
studied the influence of chemical composition of the smectite-rich
bentonite on its geotechnical and petrophysical properties. They stated
that the differences in bentonite quality and smectite quantity influence
the permeability.
The urbanization and land development in Egypt started more than
three decades ago. The construction activities extended from the narrow
district in the Nile Valley and Delta toward the vast desert fringes. These
deserts are built up of Eocene to Pliocene rocks that consist of several
expansive beds. These expansive beds produced many engineering
problems for the founded structures. Some of these problems were
studied by Moustafa et al. (1991), Abd-Allah (1998) and Abu Zeid et al.
(2004). The foundation levels of four new-built cities, east of Cairo are
concerned in the present study. The Eocene and Miocene clays of these
levels were deposited in shallow marine environment as reported by Said
(1962) and Strougo (1985). The main aim of the present study is to
identify the mineralogical and chemical compositions of the Eocene and
Miocene shallow marine clays in order to assess their influence on their
geotechnical properties.
Methodology
Twenty-five clay samples were collected at the foundation levels of four
new-built cities, east of Cairo (Fig. 1). Fifteen samples from the Upper
Eocene Wadi Hof Formation at the foundation levels of the El Mokattam
and El Qattamiya cities and ten samples from the Marine Miocene unit of
the Lower-Middle Miocene age at the El Obour and El Sherouq cities.
Intact samples were directly put in aluminum foils in the sites; each foil
was then pressed to release the air. In order to study the actual rock
characteristics, different investigations were performed on whole samples
without going to separation methods. However, calculation of
smectite/kaolinite ratios was performed on separated clay fractions. The
initial moisture content and bulk density were measured based on the
procedures described in ASTM, D2216 and D2937 (1994), respectively.
The swelling limits and pressure (using oedometer test) were measured
as described in ASTM, D4318 and D2435 (1994), respectively. The grain
size analysis was performed as described in ASTM, D421 and D422
(1994).
Abd-Allah et. al.
144
60 Km
Nile
River
Upper Eocene clays Miocene clays
Cairo-Suez road
31º 32º
30º
31º
30º
32º31º 30`
El Mokattam
El Qattamiya
El Obour
El Sherouq
Mediterranean Sea
Nile
River
Nile
Delta
Eastern
Desert
Western
Desert
C A I R O
60 Km
Nile
River
Upper Eocene clays Miocene clays
Cairo-Suez road
31º 32º
30º
31º
30º
32º31º 30`
El Mokattam
El Qattamiya
El Obour
El Sherouq
Mediterranean Sea
Nile
River
Nile
Delta
Eastern
Desert
Western
Desert
C A I R O
Fig. 1. Location map of the study area (left) and the outcrops map of the upper Eocene and Miocene clays (right). Stars indicate the locations of the studied cities.
The mineral compositions of fifteen clay samples were examined using X Ray Diffraction (XRD) and Scanning Electron Microscope (SEM) Techniques available at Ain Shams University. The chemical analyses (Major and trace elements) of the clay samples were carried out using ICP-OES Technique available at the Groundwater Research Institute, Al-Kanatar Al-Khayria, Egypt.
Results and Discussion
In hand specimens, The Upper Eocene samples are mainly laminated and fissile mudstone, whereas few samples are massive. The laminations are mostly due to change in color from yellow to dark red and reddish brown, occasionally black. They are also varied in thickness. Calcite, fibrous gypsum, halite, manganese and iron oxides are the principal cement materials found in both the laminated and massive samples, the iron nodules and concretions are present in some samples. On the other hand, the grey to green massive samples of the Miocene mudstone are partially cemented, fissile and laminated.
Mineralogical and Chemical Characteristics
The X-ray diffraction analysis of the bulk samples shows that the main non-clay minerals are quartz, halite, feldspars, gypsum and calcite (Fig. 2). On the other hand, the main clay minerals are smectite (Na-montmorillonite) and kaolinite while illite is recorded only in three samples (Fig. 3). Based on the semi-quantitative calculation of Carver (1971), the smectite ranges from 62.68% to 85.04% with an average of
Mineralogical and Chemical Compositions of Shallow Marine Clays 145
73.42%, Kaolinite varies from 14.96% to 37.32% with an average of 26.43% (Table 1). Figure 4a shows parallel smectite platelets in a very expansive soil from El Mokattam City and Figure 4b shows quartz grains in a collapsed soil from El Qattamiya City.
S:smectiteK: kaoliniteQz: quartz F: feldsparsH: halite G: gypsum C: calcite
24
19
14
9
Inte
nsi
ty (
arb
itra
ry)
2 Ө (degree)
Fig. 2. Representative XRD diffractograms of selected bulk samples (9,14,19,24) from the
study area.
Fig. 3. Selected X-ray diffractogram of clay fraction of sample number 3, El Mokattam
area. Symbols as in Fig. 2.
Abd-Allah et. al.
146
a
b
Fig. 4. SEM back scattered electron images of (a) shale sample showing well
developed parallel smectite platelets in a very expansive clay (sample
No. 5, El Mokattam City), (b) clayey sandy siltstone sample showing
quartz grains with few platy structure of clay minerals in a collapsed
soil. (sample No. 12, El Qattamiya City).
Mineralogical and Chemical Compositions of Shallow Marine Clays 147
Table 1. Semi-quantitative percentages of clay minerals by using the calculation method of
Carver (1971) and the non-clay minerals.
The chemical data (Table 2) revealed that SiO2 contents range from
20.7% to 71.5% with an average of 47.9%, whereas Al2O3 contents vary
between 9.29% and 27.2% with an average of 19.5%. The SiO2 contents
are mainly derived from quartz in sand and silt size fractions, whereas the
main source of Al2O3 is the clay minerals, in addition to, a few amount of
feldspar minerals. Samples 1 and 12 have low Al2O3 contents (11.1 and
9.29%, respectively) and low clay contents (6.68% and 4.8%,
respectively). Although sample 7 has low Al2O3 content (11.6%), it has a
moderate amount of clay fraction (27.85%) (Tables 2 and 3). This may
reflect an ionic substitution of Ca, Na, Li, Ba and Cr for Al in the clay
mineral structures. This particular sample has high to moderate contents
of these elements (Table 2). The negative relation between SiO2 and
Al2O3 indicates that both oxides are derived from different sources (Fig.
5a).
Locality sample
No.
Smectite
%
Kaolinite
%
Illite
%
Non-clay minerals
1 83.93 16.07 0 quartz, halite, goethite, gypsum
3 72.91 27.09 0 quartz, gypsum
4 74.16 25.84 0 quartz, halite, calcite
El
Mokat
tam
6 70.05 29.32 0.63 quartz, feldspars, gypsum
7 75.38 24.62 0 quartz, feldspars, goethite
9 69.54 28.87 1.59 quartz, halite
11 85.04 14.96 0 quartz, halite, calcite
12 72.52 27.48 0 quartz, halite, feldspars, goethite
El
Qat
tam
iya
14 71.43 27.91 0.66 quartz, feldspars, gypsum, halite
16 71.67 28.33 0 quartz, halite, gypsum
19 77.48 22.52 0 quartz, halite
El
Obour
20 73.6 26.4 0 quartz, feldspars
23 70.99 29.01 0 quartz, halite
24 62.68 37.32 0 quartz, calcite
El
Sh
ero
uq
25 74.54 25.46 0 Quartz
Abd-Allah et. al.
148
LO
I: L
oss
On I
gnit
ion.
( -
)
Bel
ow
det
ecti
on l
imit
:
Det
ecti
on l
imit
for
P2O
5 =
0.1
4 %
, fo
r L
i an
d P
b =
33 p
pm
, fo
r C
d a
nd C
u =
1 p
pm
, fo
r C
r =
0.0
5
Tab
le 2
. M
ajo
r an
d t
race
ele
men
t co
nte
nts
of
the
stu
die
d s
hall
ow
mari
ne
cla
ys.
Mineralogical and Chemical Compositions of Shallow Marine Clays 149
Clay minerals such as smectite, illite and chlorite show ionic
substitution of Fe2+
, Fe3+
and Mg2+
for Al3+
(Velde 1995). This is in line
with the obtained results of the present study where direct correlations
exist between these cations (Fig. 5b,d). Consequently, the Fe and Mg are
strongly related to Al and clay minerals. A further support for this
conclusion is obtained from the negative correlation between SiO2 and
both Fe2O3 and MgO (Fig. 5c,e). Another important form of the Fe3+
is as
cementing material as indicated by the presence of goethite (Table 1).
Mn occurs as a substitution for Fe, Mg (Velde 1995) or as MnO cement
on the rock surfaces. Ca commonly exists in the cementing materials as
evident from the presence of calcite (Table 1). Most of the studied
samples have low K contents correlating with the absence of illite as a
mineral constituent of clay fractions. Na+ cations occur either as a main
constituent in the Na-montmorillonite or in halite cementing material.
c
80
R = - 0.81
0
5
10
15
20
0 20 40 60
SiO2 %
Fe2O
3 %
d
%
R = + 0.55
0
2
4
6
8
0 10 20 30
Al2O
3
Mg
O %
a b
Al2O3 %
R =+ 0.71
0
5
10
15
20
0 10 20 30
Fe2
O
3 %
R = - 0.82
0
10
20
30
40
0 20 40 60 80
SiO2%
Al 2
O3
%
SiO2 %
7
80
R = - 0.68
0
1
2
3
4
5
6
0 20 40 60
Mg
O %
e
Fig. 5. Bivariant plots between some of
the major oxides.
○ El Mokattam City (Samples 1-6)
● El Qattamiya City (Samples 7-15)
▲El Obour City (Samples 16-20)
∆ El Sherouq City (Samples 21-25)
Abd-Allah et. al.
150
The clay particles are generally composed of platelets having
negative electrical charges on their surfaces and positively charged edges
(Velde 1995). This results in a high chemical activity of clay surfaces and
a consequence interaction with ions in aqueous solution. The negative
charges are balanced by cations such as Zn2+
, Cu2+
, Pb2+
, Co2+
, V2+
, Ti3+
and others. These cations are present in general in the groundwater
and/or in the water basin during the deposition. They are attached to the
surfaces of the platelets by electrical forces.
In the present study, Cu and Zn are more related to the clay contents
where they have strong positive and negative correlations with Al2O3 and
SiO2, respectively (Fig. 6a-d). Also, the clay minerals related oxides such
as Fe2O3 and MgO show strong positive correlation with Cu and Zn (Fig.
6e-f). Therefore, heavy metals such as Cu and Zn have similar adsorption
behavior on the surfaces of clay minerals.
Geotechnical Properties
The physical and geotechnical behaviors of the mudstone are
influenced by many factors such as mineralogical composition, chemistry
of clay particles, structure, environmental conditions, soil water
chemistry, moisture content and fabric (Nelson and Miller 1992). Croft
(1968) suggested that soils with large liquid limit (>60%) and plasticity
indices (>25%) invariably contain expansive clay minerals. The term
expansive soil applies to soils, which have the tendency to swell when
their moisture content increases (Sivapullaiah et al. 1996). The moisture
may increase because of rain flooding, leaking water or sewer pipes or
due to reduction in surface evapotranspiration when an area is covered by
buildings or pavement. Soils containing the clay mineral montmorillonite
(smectite) generally exhibit these properties (Komine and Ogata 1996).
The data of the grain size analysis of the studied samples show low sand
percentages compared to both silt and clay. The average values of sand,
silt and clay contents are 7.6%, 47.32% and 44.94%, respectively (Table
3). According to the textural classification of Greensmith (1989), the
collected samples from the foundation levels of the El Mokattam and El
Qattamiya cities are classified as clay to sandy silt whereas those
collected from the foundation level of the El Obour city are categorized
as silty clay to silt and from El Sherouq city are silty clay to clayey silt.
The mudstone from the study area have averages initial moisture content
and bulk density of 7.14% and 2.05 gm/cm3, respectively (Table 3).
Mineralogical and Chemical Compositions of Shallow Marine Clays 151
Table 3. Sand, silt and clay percentages and values of the physical and geotechnical
properties of the studied shallow marine clays.
S.N.
Init
ial
mo
istu
re c
on
ten
t %
Bu
lk d
ensi
ty g
m/c
m3
San
d %
Sil
t %
Cla
y
%
Liq
uid
li
mit
%
Pla
stic
li
mit
%
Sh
rin
kag
e li
mit
%
Pla
stic
ity
in
dex
%
Liq
uid
ity
in
dex
Co
nsi
sten
cy i
nd
ex
Fre
e sw
elli
ng
%
Act
ivit
y
Sw
elli
ng
p
ress
ure
MP
a
1 7.7 2.11 25.26 68.05 6.68 56.4 18.4 11.4 38.1 -0.281 1.278 25 5.7 0.5
2 10.1 2.02 9.41 66.07 24.52 76.9 24 12.7 52.9 -0.263 1.263 95 2.16 -
3 8.4 2.22 0.97 3.96 95.07 86.4 25.6 12.7 60.9 -0.283 1.281 88 0.64 3.6
4 5.7 2.06 1.13 40.38 58.49 68.2 27.3 15.9 40.9 -0.528 1.528 100 0.699 4.4
5 5.4 2.04 2.45 82.55 15 44 17.5 12.1 26.5 -0.457 1.457 30 1.767 -
6 4.8 1.94 24.02 1.48 74.5 67.8 28 16.4 39.9 -0.582 1.579 398 0.536 8.83
7 2.7 2.01 48.15 24 27.85 51.4 23.1 15.5 28.3 -0.72 1.72 135 1.016 -
8 5.9 1.97 26.65 21.05 52.3 60.4 31.5 20.5 28.9 -0.88 1.89 190 0.553 0.58
9 6.1 1.54 4.82 0 95.18 84.8 37 19.7 47.8 -0.65 1.65 290 0.502 3.73
10 4.4 1.98 0.96 26.77 72.27 56.3 28.1 18.5 28.2 -0.84 1.84 183 0.39 -
11 10.8 2.07 0.46 0 99.54 76.3 41.6 25 34.7 -0.89 1.89 140 0.349 6.4
12 6.9 1.75 32.25 62.96 4.8 43.7 22.4 16.3 21.3 -0.73 1.73 10 4.438 0.05
13 9.3 2.15 7.62 84.22 8.16 60.6 35.1 23.7 25.5 -1.012 2.01 60 3.125 -
14 7.4 1.97 9.58 81.79 8.63 41.4 29.3 23.8 12.1 -1.81 2.81 60 1.402 -
15 4.9 2.22 9.23 84.78 5.99 56.4 31.9 21.8 24.5 -1.102 2.1 70 4.09 -
16 5.4 2 5.51 84.21 10.3 56.8 34.8 24.5 22 -1.34 2.34 80 2.14 5.6
17 7 2.18 6.5 75.23 18.24 86 33.9 17.5 52.1 -0.52 1.52 80 2.86 -
18 8 2.08 0.12 21.5 78.36 88.9 41.5 22 47.4 -0.71 1.71 119 0.61 -
19 7.1 2.13 0.21 47.19 52.6 88.8 38.2 19.7 50.6 -0.62 1.62 119 0.96 2.5
20 12.1 2.05 0.8 48.62 50.6 84 33.4 17.4 50.6 -0.42 1.42 138 1 4
21 8.5 2.1 0.02 46.2 53.8 97.4 43.1 21.4 54.3 -0.64 1.64 115 1.01 -
22 5 2.16 0.41 54.2 45.4 77.5 31 16.9 46.5 -0.56 1.56 110 1.02 3.63
23 5 2.13 0.19 40.11 59.7 79.8 38 21.3 41.8 -0.79 1.79 150 0.7 5.8
24 7.7 2.18 4.94 59.13 35.93 67 29.3 17.4 37.8 -0.57 1.57 125 1.05 -
25 10 2.03 3.03 39.66 57.31 103.1 42.2 19.9 60.9 -0.53 1.53 180 1.06 -
Av 7.14 2.05 7.6 47.32 44.94 72.52 32.3 18.75 40.2 -0.71 1.7 123.1 1.54 -
Abd-Allah et. al.
152
Initial moisture content shows a general direct correlation with bulk
density of the sediment until the optimum limit of moisture content
(water content at which the sediment has a maximum dry density). After
this limit, the relation becomes reversible because the water density is
lower than the density of other solid particles of the sediment (Komornik
and David 1969). In the present study, clay structures, cement materials
and grain size distribution cause a non-significant relationship between
a b
Fe2O3%
c
(pp
m)
Cu
R = - 0.6
0
20
40
60
80
100
0 20 40 60 80
SiO2 %
e
R = + 0.5
0
20
40
60
80
100
0 5 10 15 20 25 30
(pp
m)
Cu
R = + 0.7
0
20
40
60
80
100
0 5 10 15 20 25 30
Al2
O3 %
(pp
m)
Cu
d
R = - 0.67
0
5
10
15
20
0 20 40 60 80
(pp
m)
Zn
SiO2 %
f
0
5
10
15
20
0 2 4 6 8
MgO %
(pp
m)
Zn
R =+ 0.82
R = + 0.67
0
5
10
15
20
0 5 10 15 20 25 30
(pp
m)
Zn
Al2
O3 %
Fig. 6. Bivariant plots between each of Cu and Zn and the Al2O3, SiO2, Fe2O3 and
MgO. See the caption of Fig. 5 for symbols.
Mineralogical and Chemical Compositions of Shallow Marine Clays 153
the initial moisture content and bulk density (Fig. 7). Nelson and Miller
(1992) stated that initial moisture content influences the shrink-swell
potential relative to possible limits, or range, in moisture content. The
initial moisture content also influences the clay bulk density and
consistency (Bell 2000). Therefore, the initial moisture content shows
positive correlations with both liquid and plastic limits and a weakly
negative correlation with the free swelling (Fig. 7).
+1
-1
+1
-1
Bulk Density
(gm/cm3)R= 0.14
Liquid Limit
%
R= 0.47
Plastic Limit
%
Initial Moisture
Content
(I.M.C.)
Free Swelling
%
R= -0.17
R= +0.34
+1
-1
+1
-1
Bulk Density
(gm/cm3)R= 0.14
Liquid Limit
%
R= 0.47
Plastic Limit
%
Initial Moisture
Content
(I.M.C.)
Free Swelling
%
R= -0.17
R= +0.34
Fig. 7. Correlation coefficients (R) between Initial Moisture Content (I.M.C) and plastic
limit, liquid limit, bulk density and free swelling.
The average liquid, plastic and shrinkage limits of the studied clay
samples are 72.52%, 32.3%, and 18.75%, respectively (Table 3). Based
on the classification of Snethen et al. (1977), the studied clays are
considered to have marginal to high swell potential except three samples
that have low swelling potential. The values of the liquid limit and
plasticity index of the studied shallow marine clays are higher than the
corresponding values of the brackish, fresh water and saline water Recent
clays reported by Boone and Luteneger (2000) whereas the plastic limit
values are nearly the same. Stavridakis (2005) reported that sand and
smectite contents of cement treated clayey mixtures have a strong
influence on strength, slaking and liquid limit. The average values of
plasticity, liquidity and consistency indices of the studied samples are
Abd-Allah et. al.
154
40.20, -0.71 and 1.71 respectively (Table 3). These indices revealed that
these samples represent semi-plastic solid to hard consistency clays.
Awad et al. (2005) stated that the Eocene clays of the same area are
medium to very high plastic soil while the Miocene clays are high to very
high plastic soil.
Fig. 8. A site photograph of a fractured building founded on an expansive clay bed in El
Qattamiya city.
The expansive properties of clays could be identified by measuring
both of the free swelling and swelling pressure. Sediments of free swell
values as low as 100% may exhibit a considerable expansion in the field
when wetted under light loading (Holtz and Kovacs 1981). The studied
clays vary markedly between low to very high swelling where the free
Mineralogical and Chemical Compositions of Shallow Marine Clays 155
R= + 0.59
0
20
40
60
80
100
4 6 8 10
Liquid Limit %
Cla
y %
R = - 0.41
0
20
40
60
80
100
4 6 8 10
Liquid Limit %
Sil
t %
a b
Cla
y %
R = - 0.25
0
20
40
60
80
100
1 2 3 4
Plastic Limit %
R = + 0.44
0
20
40
60
80
100
1 2 3 4
Plastic Limit %
Sil
t %
c d
40
Free Swelling % Free Swelling %
Cla
y %
R = +0.65
0
20
40
60
80
100
0 10 20 30 40
R = - 0.71
0
20
40
60
80
100
0 10 20 30
Sil
t %
e f
Fig. 9. Bivariant plots between both of clay and silt contents and the swelling properties
of shallow marine clays. See the caption of Figure 5 for symbols.
swelling values range from 10 to 290%. On the other hand, the swelling
pressure values (determined by pre- swell sample method using oedometer)
range between 0.05 MPa to 8.38 MPa (Table 3). The highly expansive beds
produced many engineering problems for the founded constructions in the
studied cities. Figure 8 shows a site photograph of a fractured building
founded on an expansive clay bed in El Qattamiya city. Ground fractures
have occurred in El Mokattam, Qattamiya and El Obour cities whereas the
slope failures took place along the southern slope of the Mokattam city.
Abd-Allah et. al.
156
Generally, these engineering problems have affected the stability of the
buildings and other constructions in these cities. Some of these
problems were studied by Moustafa et al. (1991), Abd-Allah (1998)
and Abu Zeid et al. (2004). The activity of the clay samples varies
between inactive to active clays. The wide variation of these swelling
parameters are attributed to several factors such as clay type and
percent, primary structures (massive, laminated and fissile), type and
concentration of the cement materials and the fine sands content
present as fine laminas. These laminas act as cushions diminishing the
swelling potentiality. Feda (1995) and Cheng et al. (2004) stated that
the sample structures, swelling and cementation are the main factors
affecting the shear strength of the clays.
The swelling properties of the studied samples are increased by
increasing the clay percentages and decreased by increasing the non-
clay minerals, particularly quartz. The latter constitutes the main
component of sand and silt sizes (Fig. 9a-f). Clay minerals do not
behave similarly in enhancing swelling potential. While smectite is
highly expansive, kaolinite has some swelling characteristics merely
when existing in extremely fine particle sizes, less than a few tenths of
micron (Grim 1959, Mitchell 1976 and Snethen et al. 1977). Smectite
minerals have a very high surface area activity (≈7.2) compared to
kaolinite (≈0.38) (Mitchell 1976). The very high activity of smectite
minerals enhances their ability to adsorb water on its surfaces and
increases the initial moisture content. The percent-ages of both
smectite (S) and kaolinite (K) were semi-quantitatively calculated by
using the calculation method of Carver (1971) in order to investigate
the effect of mineral types on the physical and swelling properties of
the studied clays. S/K ratio displays non-significant correlations with
the activity, initial moisture content, liquid limit, plastic limit, free
swelling and bulk density (Table 4). These non-significant
relationships could be related to other factors such as the variable
contents of sand and silt, adsorption of some heavy metals on the clay
platelets and the presence of iron nodules and concretions, which affect
mainly the bulk density.
Mineralogical and Chemical Compositions of Shallow Marine Clays 157
Table 4. Correlation coefficients between smectite/kaolinite ratio and the swelling properties
of the studied clays.
Ratio Correlation
coefficients (R) Swelling properties of shallow marine clays
+ 0.34 Initial Moisture Content
+ 0.32 Activity
+ 0.2 Bulk Density
+ 0.01 Liquid Limit
+ 0.025 Plastic Limit
Smectite/Kaolinite
- 0.25 Free Swelling
Influence of Chemistry on Geotechnical Properties
The chemical composition of the clays depends mainly on the
chemistry of the main minerals, cementing materials and adsorbed
cations and anions on the surfaces of clay minerals. Mitchell (1976)
suggested that the swelling and other geotechnical properties of the soil
are controlled by the chemistry of soil water and soil components. For the
same soil mineralogy, more swelling would occur in a sample having
exchangeable Na+ cation than in a sample with Ca
2+ or Mg
2+ cations. In
addition, leaching of a salt from the clay pore fluid might enhance
swelling potential.
In the present study, SiO2 is mainly derived from sand and silt
fractions and partially from the clay fraction. Therefore, the SiO2 content
is negatively correlated with the parameters related to the clay content
such as liquid and plastic limits, plasticity index and swelling pressure
(Fig. 10a,c,e,g). On the other hand, Al2O3 is more related to clay contents
where it shows positive correlations with liquid limit, plastic limit, free
swelling, and swelling pressure (Fig. 10b,d,f,h).
Some elements such as Fe, Mg, Mn, and Ca are present in clays
either as constituents of cement materials or as cations proxy for Al
(Velde 1995). Thomson and Ali (1969) mentioned the reliance of the
swelling characteristics of the soil on the exchangeable ions. In the
present study, the presence of Fe and Mg as proxy for Al is more
dominant than being as components of cement materials. This outcome is
obtained from the similar behaviour of the oxides of these elements and
Al2O3 with respect to relation with geotechnical parameters. In addition,
Fe2O3 and MgO contents show positive correlations with Al2O3 content
Abd-Allah et. al.
158
(Fig. 5b,c) and with liquid limit, plastic limit and plasticity index (Fig.
11a,f). The substitution of Al by Mg and other divalent cations results in
a negative charge in the crystal lattice of the clay minerals. This charge is
generally balanced later by a monovalent cation such as Na+ and K
+,
which are available in the groundwater and during diagensis process.
This behavior of substitution-balance is supported by the considerable
contents of Na2O and K2O (Table 2). The presence of halite as a cement
material represents another source of Na in the studied samples. Zn as
one of the heavy metals behaves similarly to Fe and Mg with respect to
their relations with geotechnical parameters. Zn also shows positive
correlations with liquid limit and plasticity index (Fig. 11g,h). This
reflects the common property of clay minerals and smectite in particular
to adsorb heavy metals from the surrounding solutions (Velde 1995).
Compared to Fe2O3 and MgO, the effect of MnO as a cement
material is more obvious in the studied samples as revealed from its non-
significant correlations with plastic limit and activity and the slightly
positive correlation with liquid limit and plasticity index (Fig. 12a-e).
The main sources of Ca in the study clays are calcite and gypsum
cements. This is indicated from the negative correlations of CaO with
liquid limit, plastic limit and plasticity index (Fig 12f-h). Ca from cement
materials becomes more active when exposed to groundwater and
dissolution processes. It could replace Na and K in the clay mineral
structures. This reaction creates positive charges on the clay crystal
lattice that is mostly balanced by anions from the surrounding
environment. For the same soil mineralogy, more swelling would occur
in a sample having exchangeable Na cation than in a sample with Ca or
Mg cations (Mitchell 1976). The soils with adsorbed Na cation are
relatively more plastic at low water contents and posses smaller shear
strength than the soils with adsorbed Ca cation (Murthy 1977).
Therefore, the hydrated high calcium lime and dolomite lime are used for
stabilization of expansive soils and improve their strength (Moore and
Jones 1971; Ramadan 1996 and Rao et al. 2001). Godin (1962) stated
that the clayey soils with liquid limit less than 40% and plasticity index
less than 18% are stabilized successfully by using economical amounts of
cement.
Mineralogical and Chemical Compositions of Shallow Marine Clays 159
R = +0.6420
40
60
80
100
120
10 20 30
Liq
uid
Lim
it %
R = - 0.50
0
20
40
60
80
100
120
0 20 40 60
Liq
uid
Lim
it %
SiO2 % Al2O3 %
a b
SiO2 % Al2O3 %
R = +0.27
0
100
200
300
400
500
10 20 30
%
Fre
e S
we
llin
g %
R = - 0.24
0
100
200
300
400
500
0 20 40 60
%
Fre
e S
we
llin
g %
e f
g
R = +0.57
0
2
4
6
8
10
10 20 30
Sw
elli
ng
Po
ten
tia
l
MP
a
R = - 0.42
0
2
4
6
8
10
0 20 40 60
Sw
elli
ng P
ote
nti
al
MP
a
SiO2 % Al2O3 %
h
R = +0.590
10
20
30
40
50
10 20 30
Pla
sti
c L
imit
%
R = - 0.42
0
10
20
30
40
50
0 20 40 60
Pla
stic
Lim
it %
SiO2 %
c d
Al2O3 %
Fig. 10. Bivariant plots between both of silica and alumina and the swelling properties
of shallow marine clays. See the caption of Fig. 5 for symbols.
Abd-Allah et. al.
160
Fe2O3%
Fe2O3%
R = +0.65
0
20
40
60
80
100
120
0 2 4 6
Liq
uid
Lim
it %
R = +0.44
0
20
40
60
80
100
120
0 5 10 15 20
Liq
uid
Lim
it %
MgO%
a b
Pla
stic
Lim
it %
R = +0.27
0
10
20
30
40
50
0 5 10 15 20
R = +0.29
0
10
20
30
40
50
0 2 4 6
Pla
stic
Lim
it %
MgO%
c d
Pla
stic
ity
In
dex
%
R = +0.43
0
10
20
30
40
50
60
70
0 5 10 15 20
R = +0.69
0
10
20
30
40
50
60
70
0 2 4 6
Pla
stic
ity
In
dex
%
Fe2O3% MgO%
e f
Liq
uid
Lim
it %
R = +0.51
0
20
40
60
80
100
120
0 50 100 150 200
Zn (ppm)
R = +0.51
0
20
40
60
80
0 50 100 150
Zn (ppm)
Pla
stic
ity
In
dex
%
g h
Fig. 11. Bivariant plots between both of Fe2O3 and MgO and the swelling
properties and between Zn and both of Liquid limit and plasticity
index of shallow marine clays. See the caption of Fig. 5 for symbols.
Mineralogical and Chemical Compositions of Shallow Marine Clays 161
Summary and Conclusions
Quartz, halite, feldspars, and calcite are the main non-clay minerals
of the shallow marine clays from the Eocene and Miocene foundation
beds, east of Cairo. The clay minerals of these rocks are Na-
montmorillonite and kaolinite with minor illite. The Na-montmorillonite
MnO% MnO%
R = - 0.02
0
10
20
30
40
50
0 0.1 0.2 0.3 0.4 0.5
Pla
stic
Lim
it %
R = - 0.05
0
100
200
300
400
500
0 0.1 0.2 0.3 0.4
Fre
e S
wel
lin
g %
a b
R = - 0.1
0
1
2
3
4
5
6
0 0.1 0.2 0.3 0.4 0.5
MnO%
Act
ivit
y
R = +0.23
0
20
40
60
80
100
120
0 0.1 0.2 0.3 0.4
MnO%
Liq
uid
Lim
it %
c d
R = +0.31
0
20
40
60
80
0 0.1 0.2 0.3 0.4 0.5
MnO%
Pla
stic
ity
In
dex
%
R = - 0.36
0
20
40
60
80
100
120
0.5 1 1.5 2
CaO%
Liq
uid
Lim
it %
e f
R = - 0.57
0
10
20
30
40
50
0 0.5 1 1.5 2 2.5
CaO%
Pla
stic
Lim
it %
R = - 0.16
0
20
40
60
80
0.5 1 1.5 2
CaO%
Pla
stic
ity
In
dex
%
g h
Fig. 12. Bivariant plots between both of MnO and CaO and the swelling properties of
shallow marine clays. See the caption of Fig. 5 for symbols.
Abd-Allah et. al.
162
ranges from 62.68% to 85.04% whereas Kaolinite varies between
14.96% to 37.32%. The SiO2 content is mainly derived from quartz
mineral in sand and silt size fractions of the studied clay whereas the
main source of Al2O3 is the clay minerals. The mode of Fe and Mg
existence in these clays is either as main constituents of smectite or as
proxy for Al in the clay mineral structure. Fe also constitutes cement
materials in the form of iron oxide. Mn exists as a substitution for Fe and
Mg and as MnO cement material. The substitution of Al by Fe, Mg, Ca,
Na, Li, Ba, and Cr results in the formation of a negative charge in the
crystal lattice of the clay minerals. This charge is balanced by
monovalent cations such as Na+ and K
+ from the groundwater and during
the diagenesis process and also by adsorption of Zn, Cu, Pb and other
heavy metals from the surrounding environment.
In the studied clays, the grain size distribution, clay structures and
cement materials affect the initial moisture content and bulk density.
These clays have low to very high swelling potentiality as well as semi-
plastic solid to hard consistency. This variation in the swelling
potentiality is attributed to clay type and percent, clay structures, cement
materials and presence of non-clay minerals. The mineralogical and
chemical compositions of the shallow marine clays are very important
factors affecting their geotechnical characteristics. Some elements such
as Fe, Ca, Mn, Mg, Na, and Zn when present as substitution for Al or as
adsorption on the clay minerals structure, enhance the swelling potential.
On the other hand, these elements diminish swelling potentiality when
present as components of the cement materials such as iron and
manganese oxides, halite, gypsum and calcite.
Acknowledgments
We thank Ahmed A. Sharfeldin of the Faculty of Science, Ain Shams
University for his assistance in identification of the XRD patterns. We
are also grateful for Mohamed Abdel Aal and Abdel Samad Khafagy of
the Faculty of Education, Ain Shams University for their kind permission
to use the oedometer.
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Mineralogical and Chemical Compositions of Shallow Marine Clays 165
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