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.
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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.