Dispersion influences the erodibility of soils as well as the susceptibility to piping of earth embankments. Although the causes and consequences of dispersion are well understood, the identification of dispersive soils remains a problem.
The severe drought experienced by most of Southern Africa until recently highlighted the country's problem of water shortage. Municipalities and other local authorities have attempted to define and pin-point their water losses that are centred in the so-called 'unaccounted for' water volume.
Sedimentological studies and soil engineering tests on the red soils overlying dolomitic rocks in an area south of Pretoria revealed two distinct soil types with differences in origin and engineering behaviour. A clayey silt, comprising a mixture of aeolian and hillwash materials that had undergone substantial post-depositional alteration, occurred over most of the area and attained thicknesses exceeding 30 m in karst depressions. Sporadically overlying the clayey silt was a thin layer of sandy silt of probable aeolian origin. The clayey silt was variable in composition and engineering properties, but it was generally of low density and displayed medium to severe collapse potential. The sandy silt was more homogeneous and dense. Both soil types had probably played a role in the development of sinkholes in this and similar areas, but damage to structures here was mainly the result of collapse settlement of the clayey silt.