Mode of formation and geotechnical characteristics of laterite materials of Ghana in relation to soil forming factors

Abstract

Fairly intimate knowledge about the nature, index properties and engineering behaviour of temperate-zone soils has been built up over the years; from knowledge of particles-size distribution and plasticity it has been possible to fairly accurately infer their engineering behaviour based upon the characteristics of other soils of similar classification. As yet, however, no straightforward relationship exists for laterite materials and the particle-size distribution and plasticity do not permit useful correlations between laboratory test results and field behaviour. A study, using standard and special laboratory tests on selected temperate and tropical surface soils has concluded that these two soils are similar. Wooltorton's correlation designed for use with tropical laterites and other soils, was also shown to be applicable to research findings in connection with stringent British Ministry of Transport specifications. Most engineers who have worked with soils from both climates, however, would not concur that the field behaviour of the two soils is similar. The literature of tropical soils has reported significant influences of tropical weathering processes on the chemistry, mineralogy and morphology of laterite materials; and emphasized, that no attempt to identify the significant geotechnical characteristics of these soils can succeed, if not based on the appreciation of the tropical weathering and soil-forming processes. In this paper an attempt is made to evaluate the geotechnical characteristics of Ghanaian laterite materials. The results of the study have revealed that the soil-forming factors considerably influence the distribution of geotechnical characteristics of Ghana soils. The geotechnical characteristics are a function of the weathering conditions and degree of laterisation (clay particle coatings). Approximate ranges of geotechnical characteristics were established for each genetic fine-grained soil group on the basis of the clay content and other soil-forming factors. Similar conclusions have been reached and reported on the physico-chemical properties.