The use of sand to improve the strength of natural clays provides a viable alternative for civil infrastructure construction involving earthwork. The main objective of this note was to investigate the compressive strength of compacted clay-sand mixes. A natural clay of high plasticity was mixed with 20% and 40% sand (SP) and their compaction and strength properties were determined. Results indicated that the investigated materials exhibited a brittle behaviour on the dry side of optimum and a ductile behaviour on the wet side of optimum. For each material, the compressive strength increased with an increase in density following a power law function. Conversely, the compressive strength increased with decreasing water content of the material following a similar function. Finally, the compressive strength decreased with an increase in sand content because of increased material heterogeneity and loss of sand grains from the sides during shearing.

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.Key words: calcium sulphate, expansive clay, swelling, consolidation.

No abstract

No abstract

No abstract