EM - Escola de Minas

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Coupled numerical simulation of a tailings deposit by FEM.
(2019) Braga, Ana Luiza Coelho; Nogueira, Christianne de Lyra
Researchers have found that a valuable alternative for predicting the mechanical behavior of landfill construction is numerical simulation based on the finite element method. The results of such a numerical simulation for a sandy tailings deposit from the iron mining coupling flow and deformation are presented herein. This study investigates the influence of the construction rate, drainage system, and anisotropy of permeability on the magnitude of pore pressures generated during the construction process. The study also presents the results from different analyses considering different constitutive models including elastic, nonlinear elastic and nonlinear elastoplastic. In obtaining the constitutive parameters, the numerical results highlight the importance of having a more detailed set of conventional triaxial compression tests. Also highlighted by the numerical results is the importance of having an efficient drainage system and the necessity of taking into account the water level variation in the hydromechanical behavior of numerical simulations of landfills that are hydraulically constructed.
Coupled analyses of excavations in saturated soil.
(2009) Nogueira, Christianne de Lyra; Azevedo, Roberto Francisco de; Zornberg, Jorge Gabriel
This paper presents finite-element analyses of excavations by using a coupled deformation and flow formulation. Specific numerical procedures were implemented into the finite-element codes to simulate the excavation construction and to solve the nonlinear coupled system. The paper discusses results of two generic excavations, with analyses conducted using different constitutive models and different excavation rates. Although the constitutive model affected the magnitude and distribution of the excess of the pore-water pressure due to the excavation process, the constitutive models only slightly influenced the dissipation rate of the excess pore-water pressure. Excavation rates that were one order of magnitude smaller than the hydraulic conductivity of the soil led to results representative of drained processes. Because of the slow rate needed for drained conditions, partially drained conditions normally prevail during excavations, highlighting the importance of coupled analyses.
A numerical approach for equilibrium and stability analysis of slender arches and rings under contact constraints.
(2013) Silveira, Ricardo Azoubel da Mota; Nogueira, Christianne de Lyra; Gonçalves, Paulo Batista
Underground constructions, such as shafts, courtain walls, foundations, pipes and tunnels, use structural elements that are supported by a geological medium (soil or rock) or are used to support the geological medium loads. If the geological medium is unable to react under tension, the structural element is subjected to unilateral contact constraints and, during the deformation process, may loose contact with the surrounding medium at one or more regions. The present work proposes an alternative numerical methodology for the geometrically nonlinear analysis of structural systems under unilateral contact constraints. The nonlinear problem involves two different types of variables: the displacement field and the length and position of the contact regions. In order to solve the resulting algebraic nonlinear equations with contact constraints and obtain the structural equilibrium configuration, the present work proposes a two-level iteration solution strategy at each load step. The first solves the contact problem as a linear complementary problem using Lemke’s algorithm. The second updates the displacement field. A nonlinear beam-column element is used to model the structure, while a bed of springs is used to model the geological medium. The use of an updated Lagrangian formulation, together with continuation and optimization techniques minimize the errors along the equilibrium paths and enables one to trace convoluted non-linear equilibrium paths with a varying number of contact regions. Special attention is given to the behavior of curved unidimensional support systems such as arches and rings. The nonlinear behavior of four such support systems is studied. The results clarify the influence of the foundation position (above or below the structure) and its stiffness on the nonlinear behavior and stability of curved structures. Comparison of the present results with those found in literature demonstrates the accuracy and versatility of the proposed numerical strategy in the analysis of structural elements with unilateral contact constraints.

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