This study aims to evaluate the mechanical behavior of marl soil by replacing it with alluvial sand at 3, 5, and 10% by weight for a possible application in road geotechnics. After a geotechnical characterization of the materials used, the mixtures were characterized by the Atterberg limits test, the soil compressibility test, and the shear strength test. The results obtained showed that replacing a part of marl soil with alluvial sand had a positive impact on its mechanical behavior, as it improved cohesion and shear strength while significantly reducing compressibility and plasticity. These results confirm the possibility of using alluvial sand as a fine soil reinforcement or stabilization material.