# Abstract

An existing cut slope on Highway RS-471/BR-153 is studied. The slope is composed of the Serra Geral Formation's material: a highly altered volcanic breccia and above it a slightly altered and very fractured rhyolite. A numerical analysis of the slope is carried out in two dimensions. Fracturing of the rhyolite necessitates the use of a constitutive model for materials with families of discontinuities (Ubiquitous-joint). To simplify the analysis of the problem and to examine some of the most sensitive variables, two more analyses are made, replacing the initial model by a Mohr's constitutive model, which considers the material as continuous. The results obtained from the Ubiquitous-joint model provide an acceptable representation of the field conditions, showing a failure mechanism type of rockfall from the face of the slope in the rhyolite, and the rupture surface of the breccia, without propagation of surface failure. In the analysis, when considering both materials as continuous, it is not possible to take account the fault conditions simultaneously, and this analysis also requires values of the mechanical parameters different from those recommended in literature.

**Keywords:**

Volcanic breccia; *Serra Geral* Formation; Ubiquitous-joint; numerical models