A Brief Overview of the Typical Engineering Characteristics of Tropical Red Soils

Abstract

Tropical soils in many ways have unique characteristics that can mainly be ascribed to the compositions and micro-structures of a material developed under hot, wet soil-forming conditions. For the purpose of this article, the term “tropical soil” will loosely refer to soils formed under such conditions, predominantly through chemical weathering processes. Most of these soils contain abundant iron and aluminium oxides due to the rapid breakdown of feldspars and ferromagnesian minerals, the removal of silica and bases and the concentration of iron and aluminium oxides or sesquioxides (sesquioxide = three atoms of oxygen to two atoms of another element i.e. Al2O3 or Fe2O3). Due to the high iron content, these soils are more often than not red in colour. The unique processes and conditions of soil formation in a tropical environment directly result in material compositions and structures that influence the engineering properties of tropical soils and the determination of these properties. Tropical soils do not behave in a similar fashion to temperate zone soils and consequently do not behave as expected when using conventional laboratory testing methods. This includes the susceptibility of the material to physical and mechanical breakdown, as well as a change in material properties due to cementing of the available sesquioxides. It is the aim of this paper to summarise and discuss the established unique engineering properties associated with soils formed in a tropical environment as summarised in the existing literature.