Movimentos de massa sobre depósitos sedimentares da formação Solimões na cidade de Rio Branco (AC) – SW da Amazônia – Brasil

Abstract

Mass movements are episodes that involve residual materials (soil) or rocks, and occur in different climatic zones. Such events can be fast as slips or slow as crawls. In tropical and subtropical Brazil, the most relevant events occur in the Southeast (Rio de Janeiro; São Paulo; Minas Gerais; Espírito Santo) and South (Paraná, Santa Catarina and Rio Grande do Sul) regions. In the Northeast of Brazil, in the States of Pernambuco and Bahia, there are commonly rotational landslides. In the North, in Amazonas, Pará, Rondônia and Acre are no different, as the landslides and creeps are associated with the intensity of the rains and, in other cases, the occupation of areas of medium to high degree of slope. In this sense, in Rio Branco, mass movements occur in discontinuous areas, with no recurrences, generally in the medium and high slopes over the lithological layers of the Solimões Formation. The present research had as object of study a slope located in the Vila Nova neighborhood and, in its general objective it was proposed to investigate the mass movements, as a possible subsidy to the planning of the use and occupation of urban land. Therefore, the investigation was carried out in 4 stages: Step I. Cabinet Procedures; organization and systematization of bibliography, reading of books, articles, theses and dissertations, obtained from the Bank of Theses (Capes), IBICT portal, library of the State University of Ponta Grossa (UEPG) and, in national and international journals; criteria for defining the urban dimension and acquiring digital cartographic information; In Stage II, with fieldwork on the side, we carried out the Topographic survey; Collection of sedimentary material for laboratory analysis; Installation of the piezometer for monitoring the water table; in Stage III, in the laboratory, physical and chemical analyzes took place. Stage IV turned to the exposure of the results produced using the GIS, where the level curves were created with equidistance of 1 meter to obtain the MDT. The elevation data indicated that the slope presents relevant percentages for the medium (26%) and high (40.66%) levels. However, the slope ranges from 0 to 45% (0 ° to 25 °) estimated for relief classes between 8-20%, wavy level (49.33%) and 20-45% (12 ° - 25 °) strong wavy with 34% of the slope area. Regarding the risk indicator (IR), values considered in the high classes, 43.33% and very high 46.67% were observed. For soils, Argisols represent 51% and Plintosols 49%. With the topographic survey, convex, concave and rectilinear shapes were identified, with the concave-convex forms as the greatest set. We also found that according to depths 0-20; 20-100 and 100-300 cm, there is an increase in silt and clay, as well as a reduction in sand from the first layers. For the simulation with the CRAD model, it was found that between P2 to P7 there was average water storage of 78.57 cm. However, between P8 and P9 the storage was 112.72 and 130.71 cm respectively. At these points, the texture identified was clayey and silty-loamy due to the high concentration of silt and clay, and the occurrence of gray and sticky material, regionally typified as 'tabatinga'. The techniques, methods and procedures used were extremely important to obtain the result, which allows us to affirm that the mass movement areas are not homogeneous, therefore due to their geoenvironmental characteristics it cannot be expanded to the surroundings.