This paper presents results of an elastoplastic finite element back analysis of a shallow tunnel through residual soils. The tunnel was constructed as part of the expansion of the underground transit system in the city of São Paulo, Brazil. A comprehensive laboratory testing program on undisturbed soil samples was performed in order to characterize the stress-strain-strength behavior of the residual soils. Results from this laboratory testing program were used to calibrate a nonassociated elastoplastic constitutive model utilized to reproduce the behavior of the residual soils under stress paths typical of underground excavation. A stress transfer method is proposed to simulate, using a two-dimensional finite element analysis, the response of the soil mass to the three-dimensional advancement of a tunnel excavation. Comparisons are presented between monitored displacements from an instrumented section of the Paraíso tunnel, empirical predictions, and the results of a finite element back analysis. Good agreement is achieved between the displacements obtained from field instrumentation data and the empirical and numerical results.
Numerous socio-economic benefits are associated with the oil industry. However, problems cannot be neglected, resulting in many accidents that can occur at any production stage of this industry. A serious problem created by this industry is environmental contamination by hydrocarbons. Gasoline in contact with infiltration water, the aromatic constituents, in particular the BTEX group, partially dissolve being the first contaminants to reach the groundwater. Studies published in the literature indicate that biological degradation is the main mechanism responsible for reducing the concentration of these toxic pollutants. Laboratory studies of this kind have been conducted in small scale columns, where the biological field conditions are not well reproduced. However, studies conducted in a larger scale with structured soil, remaining closer to field conditions, evidenced biodegradation processes of BTEX. This paper presents the in situ construction, instrumentation and monitoring of a large rectangular block of undisturbed residual gneissic soil, subjected to a horizontal flow of a contaminant solution composed of water, benzene and toluene to evaluate the biodegradation of these compounds in different points of the block over time. During the period of 85 days, samples of the percolating solution were periodically collected from pre-established monitoring points and the concentrations of benzene and toluene were determined using a coupled technique of gas chromatography and mass spectrometry (GC-MS). Based on the monitoring results, decay in the concentrations of the compounds over time and along the length of the block was observed. These results indicated, consistently with the biological characterization of the soil that showed the existence of microbial degrading activity, the occurrence of biodegradation of benzene and toluene, and, by an extraction process, the retention of these compounds in soil was also verified.
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.
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.
Values of the hydrodynamic dispersion coefficient and retardation factor obtained using the traditional and cumulative mass methods of column test analysis for zinc, manganese, and cadmium in a compacted soil are compared. The soil under study is from the B horizon of a residual gneissic tropical soil used for construction of the liner for the sanitary landfill in the District of Visconde do Rio Branco, Minas Gerais (MG), Brazil. To evaluate the behavior of landfill leachate heavy metals through the soil, soil column tests were performed on samples of compacted soil. A computational program that uses an optimization procedure to generate values of the hydrodynamic dispersion coefficient and retardation factor was developed to facilitate interpretation of the results obtained by the cumulative mass method. Values of the retardation factor and hydrodynamic dispersion coefficient were not influenced by the method of determination, even when a reduced number of effluent samples was used by the cumulative mass method. The use of the cumulative mass method, based on a reduced number of pore volumes, reduces the time and cost involved in the tests.Key words: heavy metals, column test, cumulative mass method.
A construção de reservatórios altera as condições naturais de um curso d'água. Dentre as principais alterações pode-se citar a redução da velocidade do fluxo da água, o que provoca o início do assoreamento do reservatório e, consequentemente, a redução progressiva de sua vida útil. O gerenciamento de reservatórios é baseado na curva cota x área x volume, que deve ser atualizada periodicamente, uma vez que os reservatórios são sistemas dinâmicos e que são submetidos a uma redução contínua do seu volume útil devido ao processo de assoreamento. Este artigo apresenta um método prático e preciso no levantamento batimétrico do reservatório da PCH (Pequena Central Hidrelétrica) Pipoca, através da utilização de um ecobatímetro monofeixe. O reservatório está localizado na bacia do rio Manhuaçu, entre os municípios de Caratinga e Ipanema, Minas Gerais. O objetivo deste estudo foi a determinação da curva cota x área x volume do reservatório da PCH Pipoca, a obtenção de um Modelo Digital de Elevação (MDE) do relevo submerso do reservatório, a determinação do volume de água e a determinação da área do espelho d'água do reservatório. O levantamento batimétrico foi realizado a partir do planejamento de seções batimétricas espaças em 30 metros ao longo da extensão do reservatório, e de uma seção longitudinal do eixo da barragem ao remanso do reservatório. Através dos resultados obtidos, observou-se a presença de maiores profundidades próximas ao eixo da barragem, e menores profundidades próximas ao remanso e nos braços do reservatório. Palavras
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