Characterization of Some Tropical Soils for Road Pavements

Design models for pavements in developing countries are almost empirical methods. There is a need, however, to use mechanistic methods to determine in a much better way the consequences of overloading, permission to use wide-base tires instead of the commonly used dual-wheel configuration, benefits of polymer-modified asphalt mixtures, use of recycled materials, and so on. The problem is that characterization of tropical soils and granular materials is still done mainly with California bearing ratio (CBR) testing because triaxial testing equipment, and especially repeated load testing equipment, is not readily available. Although it is useful, the CBR does not give information on the resilient and permanent deformation characteristics of these materials. This paper presents work done at the Road and Railway Laboratory of Delft University on characterizing a number of tropical soils, resulting in input parameters for mechanistic design analyses. The conclusion is that these soils can be characterized effectively by means of CBR and repeated load CBR testing. Nevertheless, the use of triaxial tests is highly recommended. Furthermore, some materials originally rated as marginally suited or not suited for use in base and subbase courses can be upgraded, effectively avoiding the high costs of producing and hauling high-quality materials.