Influence of mineralogy on swelling and consolidation of soils in eastern Saudi Arabia

The mineral calcium sulphate transforms from anhydrite through bassanite to gypsum and then can convert back to bassanite and anhydrite. This transformation of calcium sulphate causes volume change that adds to the potential hazards with indigenous soils containing expansive clay minerals. Heave and settlement are the most important geotechnical problems associated with many argillaceous soils in eastern Saudi Arabia. Mineralogical evolution and engineering behaviour of such soils are governed by local geology and severe climatic and environmental conditions prevalent in the region. Based on laboratory investigations, this paper discusses the influence of mineralogy on swelling and consolidation of expansive clay, calcium sulphate forms, and their mixtures. Mineralogy is investigated using geotechnical index properties and thermal and X-ray diffraction analyses. Swelling and consolidation characteristics are directly determined and are studied in conjunction with microstructural assessment. Results indicate that under the hot and humid climate prevalent in eastern Saudi Arabia, form changes in calcium sulphate can take place in the time frame of engineering importance. The volume-change behaviour of local expansive clay depends on the form and amount of calcium sulphate present in the soil.