A note on sample drying method and natural moisture content of tropical red soils from the Republic of the Congo

Abstract

This technical note describes the effects of drying method on the reported moisture content of tropical red soils from a case study site in the Republic of the Congo, Africa. Tropical soils are often considered to exhibit unique geotechnical characteristics which are often ascribed to the chemical compositions and micro-structures of a pedogenic material developed under hot, wet, soil-forming conditions. The applicability of conventional soil index tests for the identification and classification of such soils has therefore been questioned, primarily because of the dependence of such tests on the sample preparation process and the changes to the natural soil conditions which may occur during sampling and preparation. This holds true for determination of moisture content which, expressed as a proportion of the mass of the dry solid particles, can vary markedly, depending on the precise drying procedure undertaken. It is frequently suggested throughout the literature that air-drying methods, as opposed to conventional oven-drying, should be used to determine moisture content values for these soils. The findings of this study however suggest that, whilst such drying methods may be appropriate for certain tropical soils, a variation in the reported natural moisture content results may occur depending on the drying method used.