Análise geotécnica em taludes rochosos pelo método Q-Slope em loteamento no município de Caxias do Sul, RS

Abstract

Slope instability occurs when the mobilized shear stresses equal or exceed the shear strength of the material. This behavior is observed in places where the topography is irregular and is intensified by erosive processes such as in the Serra Gaúcha, where the subtropical climate and human interference result in several cases of slope instability. Engineering projects in these regions often have as a premise the need to study the geotechnical and geometric factors that impact the stability of rocky slopes, already built or that will be exposed after the project is carried out, depending on the owner's need and in accordance with legislation. in force. The quality of these engineering projects depends on the reliability of field investigations, method applied, defined parameters, as well as the interpretation of these results. The present work aimed to perform an analysis of the geomechanical properties that drive the structural behavior of the slope, in relation to its stability, as well as classify the rock mass by the Q-Slope method, indicating favorable angles to the slope. The study area corresponds to rocky slopes of two lots of the Delta Um subdivision, in the Nossa Senhora das Graças neighborhood, in the city of Caxias do Sul/RS. These slopes are up to 8 meters high, which justifies their importance in understanding the factors that can influence stability and the possible types of failure that may occur. According to historical satellite images, the slope cuts occurred in different periods between 2011 and 2018, as a result of the opening of a street and the modification of the relief according to each planned lot. The methodology used consisted of dividing the slope into nine faces where discontinuities were surveyed. In detail, the modified Rock Quality Designation (RQD'), kinematic analysis for the identification of failure mechanisms, degree of alteration of the walls of the families of discontinuities and analysis of the external factors that influence the stability of the slopes were determined. The results showed that of the nine analyzed faces, five were stable and four were unstable to the method. With the application of the method it was possible to indicate favorable angles to the slopes studied. The method proved to be a practical and efficient tool for rock massifs little altered and homogeneous, showing results applicable in practice. However, for determinations in more complex cases, such as slopes composed of saprolites, the result showed some discrepancy between the recommended face angles and the real applicability of these angles. This is evidenced mainly in the face W01 where the indicated angle of 25º is practically the angle of repose of unconsolidated materials, as in soils. Thus, it is suggested that in more complex cases the Q-slope method should be used together with other classification methods for a detailed description and an assessment more consistent with the reality of the problem.