Milene Sabino Lana

Estabilidade dos taludes da Cava Cachorro Bravo com base em modelagem numérica por elementos finitos

This work presents a slope stability analysis in Corrego do Sitio mine, that belongs to Anglo Gold Ashanti Group. The mine is situated in the northwestern portion of the Quadrilatero Ferrifero. Deformed metamorfic rocks and significant discontinuities occur in this place, leading to geomechanical problems. The objectives of this study were to analyze failure mechanisms that occurred in the Cachorro Bravo open pit in 2003, and to evaluate the pit stability in 2006, by simulating the mining excavation effects along this period. The software Phase²6.0 of Rocsciense (Canada), which models the rock mass using the finite element method, was used. The results were satisfactory, reproducing the situation observed in the field and indicating the need for new studies to evaluate the long term slope stability.

Numerical modeling of buckling failure in a mine slope

In this work the failure mechanism of flexural buckling that occurred in Pau Branco Mine, of Vallourec & Mannesman Group, in 2002, was studied through the finite element method. The software Phase2, from Rocscience Inc. was employed in the analyses. Despite being a method applicable to continuous rock masses, discontinuities may be included in the model using joint elements. Modeling is simpler, avoiding the difficulties of using distinct element methods, due to the relative complexity of the geological section examined, where it was necessary to represent the variability of the foliation attitude, due to the pattern of the observed folds. The consideration of this variability was essential to reproduce buckling failure. Back analyses of failure mechanism were done, leading to representative values of the in situ stress state and the normal and shear stiffness modulus of the foliation discontinuities. The parameters generated by the analyses are extremely useful for further stability analyses in the phyllite slopes of Pau Branco Mine.

Influência da durabilidade no comportamento geotécnico dos filitos da Mina Pau Branco

This paper discusses the durabilitys influence on the geotechnical behavior of the West Slopes rocks of Pau Branco Mine, this being the mining site on Vallourec & Mannesman (V) property, located at Serra da Moeda, Brumadinho, Minas Gerais. At the site, the occurrence of acute fracturing and folding of the rocks, plus the effects of the local weather conditions, were responsible for forming low mechanical strength and high alteration grade rocks, favoring destabilization mechanisms. The influence that durability has on the phyllites physical properties was evaluated through slake durability tests with different alteration grade and strength phyllites. Through the same tests, an attempt was made to identify the existence of an association between the durability and the failure mode in phyllites slopes. This correlation was important to be found because it could be used as an expeditious indicative of the failure mechanism and the strength of the lithologies that exist in the slope studied. Furthermore, these studies included kinematic analysis to identify conditions for the occurrence of failures caused by discontinuities and to compare these failures to the ones observed at the mining site. For this purpose, Rocscienses software Dips 5.0 was used.

Influência da expansão urbana nos movimentos em encostas na cidade de Ouro Preto, MG

Nowadays the city of Ouro Preto is faced with large problems relating to its expansion and urban increase, due to the lack of places with adequate geothecnical conditions for building. The city has been facing the consequences of inadequate occupation of the urban environment due to excessive inhabitation, lack of areas for urban expansion and the concentration of poor people around the rivers, brooks and the surroundings. Even in the central area, which is occupied by people with good social-economical conditions, the neglect of the risk of landslides is evident. This paper discusses this question, presenting in particular the problem of occupation of Morro do Curral hill.

Comportamento geotécnico de rochas brandas na mina Córrego do Sítio, Santa Bárbara (MG)

Abstract In this work the characterization of phyllites in theCorrego do Sitio Mine, Santa Barbara, MG, is discussed,as well as some factors that influence the shear strengthalong the foliation surface. Results of mineralogicdescription, physical indices and direct shear tests ofthree areas in this mine are presented. Weathering actson the variability of some properties, such as theporosity, void ratio, dry specific gravity, and also on theshear strength, with considerable reduction of thecohesion after alterability tests. In addition, theroughness observed on the foliation surface in the rocksof Crista pit influences the rock mass behaviour,increasing its shear strength. Keywords : Weak rocks, alterability, shear strength. Mineracao Comportamento geotecnico de rochasbrandas na mina Corrego do Sitio, SantaBarbara (MG) (Geotechnical behavior of weak rocks in Corrego do Sitio mine,Santa Barbara (MG)) Manoel da Conceicao Lopes Mestre em Engenharia Mineral,DEMIN/UFOP. E-mail: manoellopes@uai.com.br

Evaluation of Rock Slope Stability Conditions Through Discriminant Analysis

A methodology to predict the stability status of mine rock slopes is proposed. Two techniques of multivariate statistics are used: principal component analysis and discriminant analysis. Firstly, principal component analysis was applied in order to change the original qualitative variables into quantitative ones, as well as to reduce data dimensionality. Then, a boosting procedure was used to optimize the resulting function by the application of discriminant analysis in the principal components. In this research two analyses were performed. In the first analysis two conditions of slope stability were considered: stable and unstable. In the second analysis three conditions of slope stability were considered: stable, overall failure and failure in set of benches. A comprehensive geotechnical database consisting of 18 variables measured in 84 pit-walls all over the world was used to validate the methodology. The discriminant function was validated by two different procedures, internal and external validations. Internal validation presented an overall probability of success of 94.73% in the first analysis and 68.42% in the second analysis. In the second analysis the main source of errors was due to failure in set of benches. In external validation, the discriminant function was able to classify all slopes correctly, in analysis with two conditions of slope stability. In the external validation in the analysis with three conditions of slope stability, the discriminant function was able to classify six slopes correctly of a total of nine slopes. The proposed methodology provides a powerful tool for rock slope hazard assessment in open-pit mines.

Applicability of geomechanical classifications for estimation of strength properties in Brazilian rock masses.

Many authors have been proposed several correlation equations between geomechanical classifications and strength parameters. However, these correlation equations have been based in rock masses with different characteristics when compared to Brazilian rock masses. This paper aims to study the applicability of the geomechanical classifications to obtain strength parameters of three Brazilian rock masses. Four classification systems have been used; the Rock Mass Rating (RMR), the Rock Mass Quality (Q), the Geological Strength Index (GSI) and the Rock Mass Index (RMi). A strong rock mass and two soft rock masses with different degrees of weathering located in the cities of Ouro Preto and Mariana, Brazil; were selected for the study. Correlation equations were used to estimate the strength properties of these rock masses. However, such correlations do not always provide compatible results with the rock mass behavior. For the calibration of the strength values obtained through the use of classification systems, ​​stability analyses of failures in these rock masses have been done. After calibration of these parameters, the applicability of the various correlation equations found in the literature have been discussed. According to the results presented in this paper, some of these equations are not suitable for the studied rock masses.

Fuzzy Algorithm of discontinuity sets

O agrupamento de descontinuidades em familias nem sempre e uma tarefa trivial, particularmente quando se utiliza apenas o diagrama de densidade de polos, metodo classico. Este e extremamente subjetivo, uma vez que o tamanho da area da celula de contagem, a sobreposicao de polos e a presenca de outliers entre as familias dificultam a definicao de suas caracteristicas. Nesses casos, e util a aplicacao de metodos numericos em consonância com o metodo classico. Para isso, esse trabalho propoe um algoritmo baseado no Metodo Fuzzy K-means, que permite reunir as descontinuidades em familias sem a influencia desses fatores. O algoritmo teve seus resultados comparados com dois conjuntos de fraturas estudados na literatura e demonstrou-se eficiente.

Movimentos em encostas de Ouro Preto, MG: o caso da Vila São José

In this work the landslides in Ouro Preto have been discussed through an example involving a landslide in a slope at Morro do Curral, situated in Vila Sao Jose. The risks of landslides due to the inadequate urban expansion at the base of the hill have been presented, pointing out the problem of the comeback of movements. The effect of chemical weathering on the rock mass behavior has been discussed. A precise field survey of the landslide has been presented, showing the geometry of the failure surface. The field survey allowed the exact reconstitution of the failure surface.