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The criteria for selecting materials for railway pavement (particle size distribution, California Support Index, and physical indexes) are not suitable for evaluating the hydraulic behavior of tropical soils under unsaturated conditions, often resulting in the rejection of soils with good mechanical and hydraulic performance. The railway trackbed is exposed to precipitation, allowing water infiltration into the pavement layers and consequently leading to moisture variation. Therefore, the present study aims to assess the moisture variation over time in the railway trackbed when subjected to the action of rainfall. For this purpose, five soils were analyzed as constituent materials of the subballast, with the infrastructure of the Carajás Railway in Brazil being used as a reference. Water retention curves and conductivity tests were conducted using the HYPROP (Hydraulic Property Analyzer) and WP4-C (Water Potential Four) equipment, and numerical modeling was developed using the IVFlow software. The numerical modeling revealed that sample 1 (lateritic sand) performed better compared to the other analyzed soils, as it exhibited lower moisture variation (3.25% above the optimum content) under the influence of rainfall and it also had low permeability. [ABSTRACT FROM AUTHOR]