To predict the stress-strain behaviour of soils under loading it is relevant the knowledge of its natural stress state, expressed by the coefficient of earth pressure at rest (K0). There are correlations in theliterature for K0 determination that comes from researches developed considering sedimentary soils,typically from temperate or cold regions. In dealing with residual and colluvium soils, typical of tropical regions, it is not appropriate to use these correlations, since K0 is affected by factors such as degree of weathering, laterization processes and suction, among others that also affect saturated sedimentary soils. This work analysed samples of a colluvium soil from a natural slope at the Pontifical Catholic University of Rio de Janeiro. For the determination of the coefficient of earth pressure at rest of the unsaturated colluvium soil, a flexible wall equipment, with a system of suction control was used. The influence of the net stress level on the value of the coefficient of earth pressure at rest was investigated under a constant suction of 10 kPa, following a loading and unloading cycle of applied vertical stress. The coefficient of earth pressure at rest of the saturated colluvium (null suction) was also determined using a stress-path, Bishop and Wesley type, servo-controlled triaxial equipment. The obtained results are presented and discussed.
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