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This paper presents the results of an elastoplastic finite-element back analysis of an excavation made on a saturated soft organic clay deposit in Rio de Janeiro, Brazil. The excavation was conducted as part of an urbanization program, in which artificial islands were to be created in a swamp along the margins of the Camboinhas Lagoon. An extensive laboratory testing program was performed on undisturbed soil samples to characterize the stress-strain-strength behavior of the involved materials. Results from this laboratory testing program were used to calibrate a nonassociated elastoplastic constitutive model implemented in the ANLOG (Nonlinear Analysis of Geotechnical Problems) code. This code is based on the finite-element method and is capable of conducting fully coupled analyses by using a variety of constitutive models. Coupled analyses were performed to simulate the Camboinhas excavation, which was conducted under plane strain condition. Field measurements of both displacements and pore-water pressures obtained during the excavation are compared with the results of the numerical simulation. Analyses of the results show that monitored in situ and numerical results are in good agreement.

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.

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ResumoNas atividades que envolvem armazenamento de estéril de mineração é necessá-ria, a realização de um estudo prévio do comportamento mecânico, tanto das pilhas de estéril, quanto do terreno de fundação. Face à complexidade relacionada a esse tipo de problema, a utilização de técnicas numéricas é indispensável, ainda que forneçam uma resposta aproximada para o problema. Desta forma, apresentam-se, nesse trabalho, os resultados de uma análise tensão-deformação-resistência com base no método dos elementos finitos (MEF), de pilhas de estéril construída pelo método ascendente e dispostas em encosta. Um modelo não linear elástico perfeitamente plástico, com plasticidade associada e de acordo com o critério de resistência de Mohr-Coulomb modificado é adotado para representar o comportamento constitutivo do material empilhado, enquanto o terreno de fundação é representado por um modelo linear elásti-co. A técnica de "ligar a gravidade" aplicada para simular a construção de aterros via MEF é adotada, nesse trabalho, juntamente com o procedimento da malha dinâmica. As diferentes configurações geométricas, tanto das pilhas, quanto do terreno de fundação, analisadas fornecem indicação de que alguns requisitos definidos pela legislação vigente devem ser reavaliados, principalmente no que diz respeito a algumas restrições geométricas, as quais deveriam ser revisitadas e melhor especificadas. Palavras

An alternative method for quality control of earthworks in mining tailing dams is described in this article. It is composed by a penetrometer, known by the acronym DCP (Dynamic Cone Penetrometer), and is used primarily in road construction (quality assessment of pavement layers). With this apparatus, strength measurement of superficial layers of natural and compacted soils can be performed, including mine sand tailings, in a fast and efficient manner. The instrument was successfully used in the construction control of an iron ore mining tailings staged dam in the Quadrilatero Ferrifero, in Minas Gerais State, and the results showed distinctly effective densification of the embankment compacted layers, but with a sort of irregularity in their spatial distribution. In addition, field control using the traditional core-cutter method was also performed for comparison between both techniques.

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