Characterization of phyllite weathering profiles developed under tropical climate on Quadrilátero Ferrífero region, MG, Brazil

Low-grade metamorphic rocks show limitations in relation to the evaluation of weathering effects on macroscopic characteristics of the rock matrix due to their fine texture. In addition, the anisotropic character and high weathering impose difficulties in the preparation of samples for laboratory tests commonly used in the acquisition of physical and mechanical parameters for geotechnical purposes. This paper presents the results of a study carried out on the characterization of weathering effects on the morphology of typical profiles and on textural and mineralogical characteristics and physical and mechanical properties of weathering products of phyllites under tropical climate. The authors selected three road cut slopes and different geological materials according to their weathered state. Samples were collected for microscopic description on petrographic thin sections, and to obtain index and mechanical properties, through point load test (PLT). Detailed descriptions were performed in the field and in situ strength was estimated with a Schmidt hammer. The results show that the geological structures had a strong influence in the weathering profile, controlling the morphology of studied profiles. Weathering process was not uniform in rocks when they reached a more advanced degree of degradation. However, physical parameters associated with mineralogy were useful in predicting and differentiation the stages of phyllite weathering. •In this paper, we present the weathering grade mapping for a phyllite mass on a highway slope in the QF region, between the historic cities of Ouro Preto and Mariana, Minas Gerais, Brazil.•The Quadrilátero Ferrífero is an important region of economic interest due to mineral exploration.•Weathering vary considerably depending on the rocktype, so it is not feasible to propose a single classification that can be applied to all rocks.•In comparison to gneisses, systematic studies on patterns, morphology and weathering classification of lowgrade metamorphic rocks are scarce.•This study demonstrates that the weathering profiles of phyllites that develop under tropical conditions lead to extensive heterogeneity and variations in properties within the rock mass, as well as nonlinear relationships between rock matrix strength and physical properties, which describe the weathering intensity.