The growing research for environmental sustainability applied in technological engineering works, with natural, non-polluting, renewable and without adequate destination guided this experimental research. The objective is to analyze the mechanical behavior of a clay soil reinforced with açaí fibers distributed randomly. The açaí fibers were chosen as reinforcement due to the large production that occurs in the north region of Brazil, that region is known for a strong consumption of açaí that generates lots of this waste, besides that these fibers presents great mechanical properties and are completely natural. Characterization, simple compression and direct shear experiments were done in several samples with fiber contents of 0.5% and 1.0% in relation to the dry soil weight. The results obtained demonstrate that the addition of the açaí fibers significantly improved the mechanical properties of the soil, altering the material rupture behavior and providing a greater peak resistance and a decrease in the post-peak fall when the composite soil-fiber is compared to the natural soil. This kind of composite has a great application in regions of larger generation of this natural waste using it in geotechnical Works as floor base, slopes reinforcements and temporary landfills on soft soils.