Estudo da erodibilidade de solos e rochas de uma voçoroca em São Valentim, RS

Abstract

The research of which this Master's Thesis results was carried out in a gully known as Buraco Fundo (Deep Hole), located in the municipality of Santa Maria, in Rio Grande do Sul. The main objective was the study of the erodibility of surface soils (horizon A/B) and rocky substrate (altered rock, siltstone and sandstone) of a typical profile of the gully area. The methodology used in this study consisted in review of the literature, field investigation, tests of characterization, indirect assessment (tests of disaggregation, infiltration and loss by immersion) and direct assessment (Inderbitzen); as well as comparision with the proposal of Bastos (1999) for estimating the erodobility of unsaturated soils in the region of Porto Alegre. The results obtained out of the indirect assessment of erodibility by means of estimating the erodibility factor (KUSLE), of assessing the potential of soil disaggregation, and of criteria based on MTC methodology are: for the soils of the horizon A/B and of the altered rock the factor KUSLE has been situated between 0,20 and 0,30, being them classified as medium erodibility rate; for the layers of siltstone and sandstone that parameter has been set between 0,30 and 0,54, allowing to characterize them as materials of medium to high rate of erodibility. The tests of disaggregation showed the weaker resistence of sandstone under flooding, owing to its low cementation. The test results based on the MCT methodology have highlighted the greater susceptibility to erosion of the sandstone layer in relation to other materials. In the direct assessment of erodibility, through Inderbitzen testing, the sandstone has been found to be more erosive (K = 0.045), mainly in air-dried samples. According to Bastos' (1999) proposal of geotechnical approach, e.g. the parameter K in natural moisture, both layers have been classified as medium to low erodibility. The result of the coefficient of erodibility KUSLE has been presented as consistent with the approach proposed by the author (KUSLE > 0.20), showing that the sandstone constituted the most erosive layer. Besides, through the analysis of Pp,200, it has been found that among the layers studied the sandstone is the most erosive one. As regards the plasticity index (PI), the ratio of dispersion (RD), and through the analysis of parameter Δc, the tendency proposed by Bastos has not been found in this work. The parameters proposed by Bastos (1999), which presented the best performance have been Pp,200, the factor KUSLE, and the erodibility criteria of MTC methodology.