Navegando por Autor "Vargas Júnior, Eurípedes do Amaral"

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Analysis of bookshelf mechanisms using the mechanics of Cosserat generalized continua.
(2004) Figueiredo, Rodrigo Peluci de; Vargas Júnior, Eurípedes do Amaral; Moraes, Anderson
Bookshelf type mechanisms are commonly used to explain antithetic accommodation of deformations caused by direct shear. Stress analysis of such mechanisms have been proposed, mainly through the use of classic Mohr circle graphical constructions. The present work introduces an alternative framework for analysis, the mechanics of generalized Cosserat continua, although maintaining the same tools (Mohr circle construction). In this type of mechanics, kinematics of the material points incorporates independent rotational degrees of freedom besides the classic translational ones. In the equilibrium equations, quantities involving moments are generated and the stress tensor is in the general case non-symmetric. Such characteristics of generalized Cosserat continua make it suitable for the analysis of Bookshelf mechanisms, as these are, in essence, rotational antithetic mechanisms induced by shear stresses having different magnitudes in perpendicular planes. The paper applies the mechanics of generalized continua to the analysis of a specific bookshelf mechanism, related to crustal extension. In the Appendices, a review of the generalized Cosserat continua and details of the graphical Mohr circle representation of stresses for such media are presented.
Application of the discrete element method for modeling of rock crack propagation and coalescence in the step-path failure mechanism.
(2013) Camones, Luis Arnaldo Mejía; Vargas Júnior, Eurípedes do Amaral; Figueiredo, Rodrigo Peluci de; Velloso, Raquel Quadros
The present study evaluates the discrete element method (DEM) as a tool for understanding the step-path failure mechanism in fractured rock masses. Initially, the study simulates crack propagation and coalescence in biaxial and triaxial laboratory tests. The results of this analysis showthat the DEMaccurately represents these processes in comparison to other studies in the technical literature. The crack propagation and coalescence processes are important in the step-path failure mechanism for slopes. Simple examples of this mechanism were modeled, and their results were compared with those of the analytical model proposed by Jennings (1970). Among the possibilities suggested by Jennings,modelingwith DEMdid not provide a good approximation for the case of coplanar cracks, forwhich failures in the intact rock bridges should only be caused by shear forces. Inmodelingwith DEM, tensile failures occur within the sliding block, generating forces that are not considered in the Jennings model. The non-coplanar crack condition provided a better approximation, since the Jennings model formulation for this case includes the tensile failure of the rock. The main advantage of the DEM over other computational tools is its micromechanical representation of discontinuous media, which permits a better understanding of the step-path failure mechanism. However, good calibration of the macroscopic parameters of the rock and its discontinuities is necessary to obtain good results.
Bayesian inference of rock strength anisotropy : uncertainty analysis of the Hoek–Brown failure criterion.
(2021) Gomes, Guilherme José Cunha; Gaona, John Harry Forero; Vargas Júnior, Eurípedes do Amaral; Vrugt, Jasper A.
Strength properties of most sedimentary and metamorphic rocks are known to vary with direction. Knowledge of this so-called rock anisotropy is of utmost importance for reliability analysis and engineering design. The purpose of this paper is twofold. First, we propose a formulation of the Hoek–Brown (HB) failure criterion, which calculates strength anisotropy using a non-uniform scaling of the stress tensor. We use two scaling factors, CN and CS , to link the orientation of the anisotropy planes with the loading direction. As we assume isotropic parameters for intact rock, our HB model formulation is relatively easy to use and has the additional advantage that it does not demand any modifications to the HB failure criterion. Second, we embed our HB model formulation in a Bayesian framework and illustrate its power and usefulness using experimental data of anisotropic rock samples published in the literature. Results demonstrate that our HB model formulation predicts accurately measured peak strengths of rocks with different degrees of anisotropy, confining stresses and anisotropy orientations. The uncertainty in peak strength of anisotropic rocks can be quite large, reiterating the need for an explicit treatment of strength anisotropy uncertainty in rock mechanics studies. The Bayesian methodology is general-purpose, and, as such, can help better inform geotechnical engineers, contractors and other professionals about rock conditions and design reliability and assist decision makers in determining the overall risks of engineering structures.
Comportamento geomecânico das rochas brandas sob fluência da Mina N4E – Carajás/PA.
(2014) Guerrero, Diego Antônio Gomez; Gomes, Romero César; Velloso, Raquel Quadros; Figueiredo, Rodrigo Peluci de; Vargas Júnior, Eurípedes do Amaral
A Mina N4E, localizada na Província Mineral de Carajás, constitui atualmente uma das unidades mais importantes da Vale S/A, por conter corpos de minério de ferro de grande extensão e alto teor. Vários cenários de instabilidades, particularmente no período entre 2001 e 2009, foram detectados ao longo dos flancos sudeste e leste da cava N4E, caraterizados por processos progressivos e lentos, mobilizando trincas de topo, deslocamentos crescentes e movimentos de massa de grande magnitude. O monitoramento de taludes tornou-se, então, uma referência dos trabalhos nas frentes de exploração por meio do levantamento topográfico de prismas dispostos em áreas de interesse no acompanhamento das instabilidades mapeadas e mediante leituras contínuas dos deslocamentos por meio de um radar de superfície tipo SSR – Slope Stability Radar, particularmente nas zonas dos flancos sudoeste e leste (cava central) da mina. O presente trabalho visou estabelecer, com base nestes registros de campo, a simulação do comportamento geomecânico à fluência das rochas brandas da Mina N4E, que constituem o arcabouço geológico regional. Estes registros foram tratados por meio de simulações numéricas pelo software Abaqus, adotando-se uma lei de potência como modelo constitutivo dos maciços rochosos. Os estudos do comportamento à fluência do maciço rochoso da Mina N4E foram aplicados a duas seções de referência da cava da mina – denominadas Sg02-2013 e Sg03-2012 – localizadas no flanco leste (cava central) e no flanco sudoeste da mina, respectivamente. Os valores dos deslocamentos induzidos no maciço rochoso da cava N4E mostraram-se bastante significativos, alcançando valores métricos e com taxas também muito elevadas (mesmo considerando períodos de tempo muito restritos). Estes resultados demonstram que, mesmo na ausência de atividades de exploração nos flancos da cava, as ações de fluência tendem a ser extremamente graves, mobilizando a movimentação do maciço em condições inaceitáveis de operação.
A cross-anisotropic elastoplastic model applied to sedimentary rocks.
(2020) Gaona, John Harry Forero; Gomes, Guilherme José Cunha; Vargas Júnior, Eurípedes do Amaral; Falcão, Flávia de Oliveira Lima; Velloso, Raquel Quadros
Strength and deformability properties of sedimentary rocks are difficult to characterize as these geomaterials show anisotropic mechanical behavior, which cannot be adequately evaluated by an isotropic constitutive model. This essay proposes a cross-anisotropic elastoplastic model to evaluate stress–strain relationships of sedimentary rocks. The approach couples the twelve-parameter Lade–Kim isotropic model with a non-uniform scaling of the stress tensor and includes two scaling parameters that link the orientation of the bedding planes with the loading direction. The anisotropic model parameters can be conveniently determined using Bayesian analysis. We illustrate our method using triaxial tests on a variety of confining stresses and bedding plane orientations for a travertine and a Tournemire shale. Our results demonstrate that the predicted maximum deviatoric stresses and the simulated stress–strain curves are shown to be in good agreement with the measured data.
A dual search‐based EPR with self‐adaptive ofspring creation and compromise programming model selection.
(2021) Gomes, Guilherme José Cunha; Gomes, Ruan Gonçalves de Souza; Vargas Júnior, Eurípedes do Amaral
Evolutionary polynomial regression (EPR) is extensively used in engineering for soil properties modeling. This grey-box technique uses evolutionary computing to produce simple, transparent and well-structured models in the form of polynomial equations that best explain the observed data. A key task is then to determine mathematical structures for modeling physical phenomena and to select the optimal EPR model. This requires an algorithm to search through the model structure space and successfully produce feasible solutions that honor a set of statistical metrics. The complexity of EPR models increases greatly, however, with the number of polynomial terms used to tune these models. In this paper, we propose an alternative EPR for modeling complex soil properties. We implement a dual search-based EPR with self-adaptive ofspring creation as model structure search strategy and couple a compromise programming tool to select a model that is preferred statistically relative to models with diferent polynomial terms. We illustrate our method using real-world data to improve predictions of optimal moisture content and creep index for soils. Our results demonstrate that the models derived using the proposed methodology can predict soil properties with adequate accuracy, physical meaning and lower number of parameters and input variables.
Estudo experimental e numérico para avaliação da estabilidade de talude em solos não saturados.
(2021) Fernandes, Hemilly Cristine Lobo; Pereira, Eleonardo Lucas; Velloso, Raquel Quadros; Pereira, Eleonardo Lucas; Bacellar, Luis de Almeida Prado; Vargas Júnior, Eurípedes do Amaral
A chuva é o principal agente provocador de movimentos de terra, tornando-se uma possível ameaça para a sociedade e um motivador para analisar a susceptibilidade de taludes aos deslizamentos. Uma das causas que explica a ocorrência dos mesmos é a redução ou eliminação de uma parcela de resistência ao cisalhamento do solo devido à diminuição da parcela de sucção, ou também chamada de poropressão negativa, em solos não saturados, gerada pela infiltração de água de chuva. Para a análise da influência da infiltração na estabilidade de um talude, deve-se ter conhecimento dos parâmetros hidráulicos e de resistência do solo. Modelos conceituais e numéricos tem sido desenvolvidos para determinação dos parâmetros hidráulicos em meios porosos não saturados, assim como a utilização de ferramentas numéricas, que auxiliam na compreensão da dinâmica e influência da chuva na estabilidade de taludes. Nesse contexto, a presente pesquisa tem como objetivo principal a avaliação da estabilidade de talude considerando meios porosos não saturados sob influência de precipitações. Para isso foram realizados ensaios de campo e laboratório para caracterização física, definição dos parâmetros de resistência do solo e o ensaio de infiltração monitorada (EIM) para obtenção de dados que foram retroanalisados numericamente visando a aquisição de parâmetros hidráulicos de solos não saturados. Essas informações serviram como dados de entrada para a determinação do fator de segurança transiente do talude em estudo. Finalmente, as análises de estabilidade sob influência de precipitações, foram capazes de representar a perda de sucção e, consequentemente, a diminuição do fator de segurança do talude ao longo do tempo analisado.
Field-scale assessment of the unsaturated hydraulic properties of residual soils in southeastern Brazil.
(2022) Gomes, Ruan Gonçalves de Souza; Gomes, Guilherme José Cunha; Vargas Júnior, Eurípedes do Amaral; Genuchten, Martinus Theodorus van; Pinto, João T. M. G.; Rosa, Felipe A.
Field tests were carried out to estimate effective unsaturated soil hydraulic properties of layered residual soilsin Rio de Janeiro, southeastern Brazil. Data of this type are important for understanding the initiation of rainstorm-induced soil landslides, which often occur in the state of Rio de Janeiro as well as other areas having similar geologicsettings and climate conditions. Tests were carried out using a simplified field approach, referred to as the MonitoredInfiltration Test, which requires only a tensiometer to measure pressure heads below the wetting front, triggered by flowfrom a Mariotte bottle which maintains a constant pressure at the top edge of the soil profile. The data can then beanalyzed by numerical inversion using the HYDRUS-2D software package. The test is relatively fast since no steady-state flow conditions are needed, and versatile since the test can be carried out quickly on steep slopes with the help of amanual auger. Soil water retention and the unsaturated hydraulic conductivity functions were obtained for a range ofyoung, mature and saprolitic residual soils. The effective hydraulic properties of the distinct residual soil layers can bequite large, reflecting a need to provide a careful analysis of field-scale hydraulic heterogeneity in geotechnical analyses.
Mechanical characterization of rock splitting planes in granitic rocks.
(2006) Almeida, Luiz Carlos Rodrigues de; Vargas Júnior, Eurípedes do Amaral; Figueiredo, Rodrigo Peluci de
Mechanics of Cosserat generalized continuum and modelling in structural geology.
(2020) Moraes, Anderson; Figueiredo, Rodrigo Peluci de; Vargas Júnior, Eurípedes do Amaral
A concepção e interpretação de modelos em geologia estrutural, especialmente os numéricos, são eminentemente baseadas nos princípios da mecânica do contínuo clássico, onde a formulação intrínseca possui alto grau de simetria em sua própria essência. No entanto, as estruturas geológicas apresentam em todas as escalas de observação um nível notável de assimetria. Por outro lado, a mecânica do contínuo generalizado de Cosserat, ao incorporar comprimentos característicos da estrutura da matéria em suas leis constitutivas e em seus critérios de ruptura, conduz naturalmente à assimetria e à heterogeneidade dos campos cinemáticos e dinâmicos responsáveis pela estruturação presente em rochas. Baseado na formulação intrínseca dos meios contínuos de Cosserat, o presente trabalho enfatiza modelos conceituais, analíticos e numéricos que sugerem uma ampliação na interpretação da gênese e do desenvolvimento de estruturas geológicas, em particular as encontradas em zonas de falhas.
Numerical analysis of sand/solids production in boreholes considering fluid-mechanical coupling in a Cosserat continuum.
(2011) Muller, André Luís; Vargas Júnior, Eurípedes do Amaral; Vaz, Luiz Eloy; Figueiredo, Rodrigo Peluci de; Gonçalves, Clemente José
Sand/solids production is a serious problem faced by the petroleum industry during production stages. Particles/groups of particles of the formation rock are produced together with pumped oil or gas causing highly damaging effects on pipes and valves. This phenomena can be caused by several factors including the stresses developed around the boreholes/perforations and fluid flow, which break and erode the rock, respectively. Numerical simulation of sand/solids production presents a considerable challenge as intricacies of failure processes must be correctly simulated. This paper presents a finite element based procedure for simulating the process of sand/solids production, considering fluid- mechanical coupling in an elasto-plastic Cosserat continuum. It is believed that the enhanced deformation modes included into Cosserat continua may contribute for proper modeling of the deformational behavior and failure modes of the cemented/non-cemented granular materials involved. Bogdanova-Bontcheva and Lippmann’s constitutive model was implemented in order to model the granular materials involved. Finally, the work presents the analysis of sand/solids production in a hypothetical borehole. For comparison purposes, different characteristic lengths of the material are adopted and analysis is also performed using standard continua.