A study of basic mineralogical, physical-chemical, and engineering index properties of laterite soils

Increasing construction activity in tropical environments has greatly expanded the requirement for engineering knowledge related to the basic properties of tropical soils. One of the most frequently encountered yet least understood variety of tropical soils are those residual surface deposits commonly identifies as laterite soils. Because of a general lack of factual data regarding index properties of these soils, generalizations attempting to characterize the engineering behavior of laterite soils have frequently been devoid of factual constraints. A detailed study has been made of selected soils, reported to be laterite soils, to establish data related to the basic chemical, mineralogical and engineering index properties of such material. All of the soils were developed in a tropical environment between the 11th and 18th North parallels of latitude. The findings have been studied to establish a correlation between the chemical, mineralogical and engineering index properties in order to point the way to more intelligent understanding and engineering usage of these soils. The findings of the laboratory study show that, from the civil engineering point of view, no distinguishing chemical, mineralogical or engineering property could be found which is sufficiently definitive to set these soils apart, as a group, from other soils. Based upon the findings, it is concluded that the persistent usage of the term "laterite" by civil engineers as descriptive of a broad group of tropical soils with similar properties, is at best misleading. The results of the correlation study show a strong relation to exist between the cation exchange activity and the activity ratio for the soils tested. This relation may be approximated by the expression CEAc=0.784(Ac)¹². A strong relation was also found to exist between cation exchange activity, activity ratio and the type of clay mineral composition for each soil tested. The relation may be clearly depicted by the use of a correlation graph which was developed for this purpose as a part of this study