Geotechnical properties of Cape Flats sands

The sand-covered coastal plain connecting the Cape Peninsula mountain chain to the southwestern Cape mainland is known as the Cape Flats. The whitish windblown sands covering this area of approximately 460 km², referred to as the Quaternary sands of the Cape Flats, provide founding for the rapid and ongoing development in the area. A knowledge of the geotechnical properties and engineering behaviour of these sands is essential for design of suitable foundations for proposed structures and earthworks associated with such developments. By combining, analysing and interpreting the wealth of existing and available geotechnical information from previous and new soil investigations undertaken in the area, the Quaternary-aged sands of the Witzand, Springfontyn and Langebaan Formations from the Cape Flats were characterised in terms of their physical properties and engineering behaviour. The sands from the study area were classified based on their grading, Atterberg limits, maximum dry density and optimum moisture content, minimum dry density, California Bearing Ratio (CBR), erodibility and corrosivity, and characterised in terms of their compressibility, shear strength, permeability, volumetric behaviour during shear including liquefaction potential, in-situ density and moisture content and specific gravity. The Cape Flats sands were found to be highly variable (with both inter- and intra-formation variation), with a wide range in many material properties, principally a function of soil texture, gradation and degree of cementation. The findings of this research may be used to form initial appreciation of the likely properties of the material and potential problem areas.