The objective of this work is to study the behavior and durability of soils reinforced with randomly distributed vegetal fibers (sisal and curauá) submitted to natural aging by their exposure to diverse environmental conditions, aiming to boost its use in earthworks. The experimental program consisted of conventional triaxial tests on sand and sand-fibers samples at zero time (sample control) and on composites exposed to agents from the external environment for up to 8 months. In order to improve the durability of these composites, it was also evaluated the mechanical behavior of these with vegetal fibers treated by surface waterproofing, with colloidal silica and styrene butadiene polymer. In order to explain the variation in the obtained results, direct tensile tests, scanning electron microscopy, infrared spectroscopy and mass loss analysis were performed on the fibers after each exposure period (0, 60, 120 and 240 days). The overall analysis of the results allowed to identify that the effects of natural aging had a significant effect on the mechanical behavior of the vegetable fibers, which consequently affected the mechanical behavior of the sand-fiber composites. Shear strength losses were more relevant and accentuated in composites with curauá fibers, indicating that these fibers, even with higher tensile strength without exposure, are more susceptible to degradation in natural environments than sisal fibers. Surface treatment of the fibers by impregnation with colloidal silica resulted in improvements in the mechanical behavior of this composite, also providing a longer fiber life with respect to degradation. Even with the loss of mechanical behavior of the fibers, after 8 months of exposure to the climatic agents, they continued to contribute as a reinforcing element in the sandy matrix, since one of the resistance parameters remained higher when compared to the sandy soil without reinforcement.