Mineralogical and chemical compositions of shallow marine clays, East of Cairo, Egypt : a geotechnical perception

الملخص EN

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