Engineering properties and mineralogical composition of expansive clays in Al-Qatif area (K.S.A.) (Saudi Arabia)

Al-Qatif is a town in the Eastern Province of Saudi Arabia where expansive soil problems are reported. This study is concerned with the determination of engineering properties and behavior of these clays by performing various laboratory tests.; A site investigation was carried out to obtain undisturbed block samples. Geotechnical properties e.g. Atterberg limits, natural water content and density, showed that Al-Qatif clays are highly expansive and are heterogeneous in nature.; Quantitative characterization to estimate the amount of anticipated volume change was carried out using conventional one-dimensional consolidometer. The results of direct swelling tests indicated high values of swelling pressure and percentage of swell.; X-ray diffraction and scanning electron microscopic analysis indicated that Al-Qatif clays are mixtures of two principal clay minerals: montmorillonite (pure smectite) and polygorskite with flaky flocculated morphology & needle form. Chemical analysis showed the presence of low amount of organic matter. All soil samples were alkaline in character with high cec values.; Laboratory evaluation of chemical stabilization was done using three types of chemicals. The results showed that 4-8% of commercial lime should be preferred for preconstruction treatment of Al-Qatif clays. Some methods of special foundation designs and floor slab construction are also suggested.