Abstract This article proposes to evaluate the application of Seismic Hazard methodologies for the study of falls of ground (FOG) that occurred in the Cuiabá underground mine. Specifically, a fall of ground that occurred in 2018 in the Serrotinho mineralized body (level 18) was elected as the object of study, since it had characteristics common to other FOGs that occurred deep in the mine. Because of the close proximity and timing of the events, another three FOGs were considered in order to understand the relationship between these rock detachment events and microseismicity. Regarding seismic hazard methods, the apparent stress ratio (ASR) could provide an overview of the evolution of apparent stress in the region. The interpolation of the ASR of microseismic events to the mine levels, in 3 of the 4 cases studied, mapped the FOG region as having a high apparent stress ratio before its occurrence. A rockburst early warning methodology, in turn, proved to be helpful in the identification of precursor conditions of a microseismic event of greater local magnitude (ML = 0.5) in the analyzed period. Although, during application of this method, some difficulties were found in identifying the right precursors patterns of the microseismic parameters.

Taludes escavados em filito, sejam para obras civis ou de mineração, são conspícuos na região do Quadrilátero Ferrífero, MG. Em sua grande maioria, verifica-se a ocorrência de mecanismos de instabilização não usuais em taludes escavados em outros materiais rochosos, como, por exemplo, o tombamento flexural. Foram realizadas 255 análises paramétricas, correspondendo a uma combinação de geometrias de talude com ângulos variando de 30º a 60º e alturas de 50 a 200 m, de ângulos da foliação variando de 40º a 80º, e de quatro diferentes classes geomecânicas de maciços. Utilizou-se o método computacional de diferenças finitas implementado no software FLAC, que permite a consideração de grandes deformações do maciço analisado (o que pode ocorrer em um talude de filito/xisto), e é especialmente apto a modelar o processo dinâmico de instabilização de um talude. Os resultados permitiram a criação de três cartas de estabilidade para as classes de maciço II, III e IV, com curvas que delimitam zonas estáveis e instáveis ao tombamento flexural, para diferentes alturas de talude. Tais cartas são adequadas para análises preliminares de projeto, nos taludes de filitos e xistos do Quadrilátero Ferrífero. Permitiram, ainda, uma melhor compreensão da mecânica do processo de instabilização de tais taludes.

Slopes in phylite, of civil works or of mining, are conspicuous in the region of the Quadrilátero Ferrífero, MG. In the great majority it verifies the occurrence of instabilization mechanisms, such as flexural toppling, not usual in slopes of other rocky materials. We used the computational method of finite differences implemented in the software FLAC who allows the consideration of great deformations of the analyzed massif (what it can occur in a slope of phylite/schist), and it is especially apt to model the dynamic process of instabilization of a slope. They were accomplished 255 parametric analyses, corresponding to a combination of slopes geometries with angles varying from 30º to 60º and heights from 50 to 200m, of angles of the foliation varying from 40º to 80º, and of four different geomechanical classes of massifs. The results allowed the creation of three stability charts for the geomechanical classes II, III and IV, with curves that define stable and unstable zones of flexural toppling, for different heights of slope. Such charts are adequate for preliminary analyses of slopes designing, in phylites and schists of the Quadrilátero Ferrífero. The computational analyses allowed, yet, a better comprehension of the mechanics of the instabilization process of such slopes.