To evaluate the stress-strain behavior of soils under loading in engineering practice it's usually required to know the natural, initial state of stresses acting in the soil mass. This is not an easy task when dealing with sedimentary soils. When it comes to tropical residual soils, this challenge is even greater due to variations in the weathering degree and soil profile moisture. The natural state of the soil is usually expressed by the coefficient of at-rest earth pressure (K_0). To determine K_0, three classes of methods can be used: correlation methods, in situ determination and laboratory tests. On this research, one rigid cell with a system of suction control was used to obtain values of K_0 in laboratory tests, three samples of gneissic residual soil with different degrees of weathering were analyzed, and each one tested in three different levels of moisture. In general, the results attended the expected trend.
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