mineralogical and chemical compositions of shallow...

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


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).


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.


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).


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.


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


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.


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.


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.


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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