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The relationship between matric or total suction and gravimetric water content, volumetric water content, or degree of saturation is denoted as the soil-water characteristic curve. This relationship has been widely used for predicting the engineering behavior of unsaturated soils. Residual and colluvium soils from tropical and subtropical regions often show bimodal-shaped soil-water characteristic curves, indicating that both micropores and macropores present in these soils govern the inflow and outflow of water. The objective of this paper is to discuss testing methods adequate for obtaining soil-water characteristic curves of bimodal shape, particularly by the combined use of the suction-plate method (suction < 10 kPa) and the filter-paper method (5 kPa < suction < 30 000 kPa). The soil-water characteristic curves of two undisturbed colluvium soils from Southern Brazil are then presented to highlight the application of those methods.

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