Preliminary identification of problem soils for infrastructure projects

Abstract

During the feasibility and planning stages of infrastructure projects, the early identification of problem materials that could affect the project can save significant costs and or redesigns later in the project. As the potentially most problematic soils are those within the top 1.0m or 1.5m of the soil profile, a mechanism for evaluating these materials without preliminary filed work and testing would be invaluable. Since 1971, the Department of Agriculture has systematically mapped the soils covering the entire land surface of South Africa, at a 1:250 000 scale. The mapping units are land types, which are defined as areas that show a marked degree of uniformity with respect to terrain form, soil type and climate. These are (coincidentally) the same criteria selected for a materials data bank for roads developed in the 1970's and must therefore be of similar use in infrastructure and particularly road engineering. As the primary aim of the soil maps was to provide information regarding the agricultural potential of the soils, comprehensive testing of various properties has also been carried out. Analysis of the Soil Maps and their accompanying information (freely available on a local web site) indicates that they can be used to identify (in broad terms) the types of soils in any area under review, and many of the accompanying potential problems. Soils such as potentially expansive materials are identified directly, potentially dispersive soils can be identified through the exchangeable sodium ion contents provided and collapsible soils through widespread exposures of sandy and residual materials of low density. In addition, a general assessment of moist areas and those with thick or thin soils or rocky outcrops, underlying dolomitic materials, saline soils, etc., can be obtained early during any project, even before any site visit has been made. Being forearmed with such information will often lead to avoiding the threat of unnecessary land expropriation, to more efficient site investigations and more economical rout alignment and to avoiding claims and delays during execution of the project