Comparisons Between Field and Analytical Behavior of an Experimental Excavation

This paper analyses the behaviour of an experimental unsupported excavation taken to failure in a soft clay deposit near Rio de Janeiro, Brazil. The excavation was originally analyzed by Pontes Filho and Medeiros (1982) assuming undrained conditions. In this paper, the same excavation is analyzed by Biot\u27s coupled theory of consolidation and deformation using linear elastic, non-linear-elastic and elasto-plastic constitutive models and simulating the excavation process in time, without a – priori hypothesis on the drainage conditions. Details of the excavation construction, geotechnical profile and instrumentation are briefly described. Subsequently, the constitutive model calibrations are discussed in view of laboratory tests available. Finally, for each excavation step, comparisons are made between surface settlement profiles, horizontal displacements and pore-pressure measured in the field and analytically calculated

Numerical modelling of the sedimentation and consolidation of tailings

The byproduct of processing rocks for the purpose of extraction of minerais is a waste which is generally referred to as tailings. These byproducts are impounded behind dams specially designed for thjs objective and are known as tailings deposits. The objective of this study is to investigate the true capacity of a reservoir when waste material is impounded. The process consists of dispersion, sedimentation and consolidation, which take place simultaneously. It is the purpose of the present study to analyze these coupled phenomena of soil formation to estimate the volume of waste that can be impounded. This is an important factor from a financiai and ecological view point. A theory is proposed which contains the sedimentation and consolidation processes. In arder to have a complete modelling of the problem an Implicit Finite Difference Code was developed. The code is based on the use of the Preissmann Scheme and the Double Sweep Method to solve the system of partial differential equations that form the sedimentation part of the problem. A new constitutive model for the characterization of the stress-strain behavior of the solid skeleton, considering the changes in the state of the material is developed. This forms an important part of the basic equation of the consolidation process coupling pore-pressure dissipation and deformation of the soil mass. A Finite Element Code is developed incorporating both nonlinearities, i.e. those arising from the material response (Elasto-Plastic Model) and those due to geometrical (Eulerian System) nonlinearities. To complement the study, the case of the disposal of a bauxite mine in a reservoir located in Saramenha, district of Ouro Preto, Minas Gerais, Brazil is considered. Comparison between numerical analysis and field measurements is made based on total and effective stresses profiles, void ratio profile and vertical displacements through the soil formation profile. The numerical analysis successfully predicts the filling of the reservoir, which helps build confidence in the numerical procedure developed in this study

Experimental study on fibre reinforced sandy soils behaviour under static loadings - drained and undrained conditions

The effect of the addition of 0.5% of randomly distributed polypropylene fibres in a round grained sand, composed mainly of silica, is presented on laboratory scale. The samples were compacted with two void ratios (0.75 and 0.63), corresponding to values of relative density of 50% and 90% respectively. 24 monotonic triaxial tests were performed, with initial effective mean pressures of 20, 100 and 200 kPa. Half of samples were tested in drained conditions, and the other half in undrained conditions. For the samples subjected to drained conditions, the effect of the fibres was identified at the post-failure stage, by showing sustained increase of strength. The positive effect of fibres could also be observed through the increase of material friction angle. In the samples subjected to undrained tests, the addition of fibres reduced the contractive behaviour, mainly for those more compacted

Análise da influência da variação de parâmetros em um modelo que simula a sedimentação de resíduos dispostos em um reservatório

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A influência da vazão do rio e da concentração de sedimentos na formação de solo em um reservatório

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ESTUDO NUMÉRICO DE FUNDAÇÕES SUPERFICIAIS SOBRE SISTEMA DE DUPLA CAMADA

Foi estudado, através do Método dos Elementos Finitos, o comportamento de fundações superficiais assentes em sistemas de dupla camada, sendo a superior artificialmente cimentada, com uma largura igual a três vezes o diâmetro da fundação. Sendo H a espessura de solo cimentado e D o diâmetro da fundação, foram feitas diversas simulações para as várias relações H/D (desde zero até 4,0). Depois de confirmada a influência da relação H/D na resposta carga x recalque de fundações superficiais, foi feita uma análise paramétrica após a qual é proposta uma nova metodologia de dimensionamento de fundações superficiais assentes em sistema de dupla camada, sendo a superior cimentada. Finalmente, a capacidade de suporte de fundações superficiais assentes em camadas cimentadas foram simuladas com sucesso através da nova metodologia apresentada. Para a prática da engenharia o método proposto, através de curvas carga-recalque, fornece boas previsões para a obtenção da capacidade de suporte de fundações superficiais

Tratamento de solos orgânicos com adição de cinza de termoelétricas e cal

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Stabilised soil layers enhancing performance of transverse-loaded flexible piles on lightly bonded residual soils

A set of crosswise-loaded flexible piles was tested in binder stabilised top sand layers embedded in lightly bonded residual soil. Slope indicators were used to measure horizontal displacements in free-headed flexible piles during all loading stages. The geometry of the cement stabilised top sand layer surrounding the piles varied from about 2 to 4 times the pile diameter and 0.1 to 0.3 times the pile length. Experimental outcomes present an important enhancement in the performance of the flexible piles under transverse load when a cement stabilised sand layer replaces top residual soil, increasing bearing capacity and reducing maximum horizontal displacements at any given working load. At large horizontal displacements (close to failure), a linear relation is observed between the lateral load and the total lateral area compressing the natural soil around the pile. This evidence helps identifying the pile-soil interaction mechanism and provides sound normalization for test results, both considered necessary steps towards the development of a design concept for predicting lateral pile response

Spread footings bearing on circular and square cement-stabilized sand layers above weakly bonded residual soil

The practice of soil-cement reinforced layers to bear shallow foundations is a feasible option in low bearing capacity soils. This paper addresses the interpretation of plate load tests bearing on compacted artificially cemented sand layers of distinct sizes and shapes (cylindrical and prismatic) overlaying a weakly bonded residual soil stratum. Static load tests were carried out on a rigid circular steel plate (diameter of 300-mm) resting on sand-cement reinforced layers with distinct areas (diameters/widths of 450, 600, and 900-mm) and constant thickness of 300-mm. The results have shown two distinct failure modes that rely on the cemented layer’s diameter/width: (a) the steel plate and the artificially cemented layer punch together into the weakly bonded residual soil, without the failure of the cemented layer, and (b) the artificially cemented layer fails. The combination of two traditional methods for predicting bearing capacity in soils was successfully applied considering the shape (and geometry) of the improved layer and the existence (or not) of interaction of the lateral of the cemented layers and the residual soil. Finally, this study highlights the importance of considering the shapes and sizes of soil-cement layers in the bearing capacity estimation (combining analytical solutions) of spread footings resting on treated layers above weakly bonded residual soils