Soil Erodibility on Cutting Slopes of Unpaved Roads

Unpaved roads have an expressive importance for a significant portion of the Brazilian population, since they allow rural population access to education and health, make connections between rural areas and urban centers, and through them the agricultural production flows. Despite the social and economic importance of these roads, it is possible to observe their construction without adequate previous studies, regarding hydric erosion and the stability of the soils present on the cutting slopes. This fact results in economic losses from the restoration of these roads and interruptions caused by instabilities in slopes. The purpose of this research is to evaluate the erodibility of soils in the unpaved road slopes at the Bom Jardim city in the mountain region of the state of Rio de Janeiro, considering the erosive processes already installed, the agricultural vocation of the municipality and the large extension of the unpaved road network. The working method began with the field survey, of road slopes with evident signs of erosion, in a micro basin subordinated to Rio Grande. After the field description of the erosive features and the soil profiles present in these slopes, the various horizons were collected for later physical and mineralogical characterization in the laboratory. The erodibility of each soil horizon was evaluated based on the results of the field observations, through the erodibility indices and the Modified Inderbitzen, conducted considering the regional average declivity and intense rainfall in a specially constructed rain simulator for this purpose. The results point to the highest erodibility of the C horizons in relation to the other horizons of the Oxisol and Ultisol studied. This fact explains the main process of observed instability, erosion at the toe of the slope and fall of the upper horizons. It is concluded that the road cutting slopes in the region should be executed avoiding the exposure of the C horizon or the altered rock, and when this is not possible, it is necessary to adopt measures that prevent water erosion.