Análise, caracterização e dinâmica em perfis de intemperismo na área urbana de Juiz de Fora - MG

Abstract

Themes related to the decomposition and fragmentation of rocks are found in an interdisciplinary area, named weathering, that goes through sciences such as Geology, Pedology, Geotechny, Geomorphology and Geography, but that is not considered as the main theme. Thus, the proposal OF this project was to investigate the weathering material, considered as the place where these processes occur. Several sites where this material occurs in the urban area of Juiz de Fora town were investigated, as well as the representativeness of these materials in a local tropical environment, based on the premise that it is representative of the weathering in the humid tropics. In order to contribute with the knowledge about the physical structure of the region, a characterization of the weathering profiles in the town of Juiz de Fora was carried out, in physical and mineral terms. Other objective included how and what are the comportament of weathering profiles, caused by their characteristics, can affect society, as in the case of mass movements. To fulfill the project's objectives, in addition to a bibliographic review, three phases were followed. The first one corresponds to the description of the weathering profile and ITS materials, in addition to the analysis done in the field and also the sampling. The second phase corresponds to the analyzes made in the laboratory and the third corresponds to the tabulation and interpretation of the results. In the field, structures and thicknesses of profile structures were measured; in the laboratory, color, texture, consistency, mineralogy, original rock and degree of alteration were analyzed. It is observed that the rocks of origin conditioned two large groups of weathering profiles with very different characteristics between them, being the texture the main differential. In one of the groups, sandy material predominates, with a very marked presence of more resistant primary minerals such as quartz. The another group has a predominance of clay minerals. the color have a variation between red, yellow and brown, predominantly. In some cases, the color is homogeneous for the entire horizon, while in other situations there is a predominance of only one color and the presence of some isolated colored points. In most of the sites, there are planes of fractures and / or faults inherited from the rocks.The selected measured planes have two preferred directions: N-S (next to NNW-SSE), NE-SW (closest to NNE-SSW). Such directions predominate, coinciding with the directions of the great geological structures in the region, and this is an indication of the material's autochthony. About the diving angles, most of the measured planes have angles less than 20 °; however, it is important to consider the presence of diving angles in the ranges of 20 ° to 45 ° and 70 ° to 90 °. These geological structures, when favorable to mass movement, appear as one of the main causes of this event. In one of the weathering profiles, where some risk assessment methods were applied, the presence of plans dip to the outside of the profile, was definitive for mass movement. The studied material plays an important role in the general context of the landscape, functioning as source material for the soils, substrate of the large part of the surface where buildings are installed. Thus, it must be well known for being well used, without offering risks to the population, as it can happens in some cases where there is an occurrence of mass movement or erosion.