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Student Number : 0418755N - MSc (Eng) dissertation - School of Civil and Environmental Engineering - Faculty of Engineering and the Built Environment / Environmental impacts from tailings impoundments differ according to their mineral constituents. Erosion is one of the processes that aggravate the environmental impacts from tailings due to the transportation of particles, and knowing the susceptibility mechanisms of those tailings particles for erosion will provide understanding of how to prevent impacts arising from erosion. Laboratory pinhole erosion tests were used to determine the susceptibility of tailings particles to erosion. Compacted tailings samples were used, as compaction is an important parameter of erosion susceptibility. The study entails investigation of factors that affect erosion from the slopes of tailings deposits in order to evaluate mitigation measures. The results could help to provide more effective methods to reduce gully formation and enhance environmental protection. It is advisable to prevent environmental impacts at the source, before they become detrimental and costly to mitigate.

Yes / This paper provides results of a comprehensive investigation into the use of waste carpet fibres for reinforcement of clay soil slopes. The interaction between laboratory scale model slopes made of fibre reinforced clay soil and surface strip footing load was examined. Results for the influence of two variables namely fibre content and distance between the footing edge and the crest of the slope are presented and discussed. Particle Image Velocimetry (PIV) technique was employed to study the deformation of the slope under the surface loading. The front side of the tank was made of a thick Perspex glass to facilitate taking accurate images during the loading stage. To study the stress induced in the slope under footing pressure, excess pore-water pressure and total stress increase were measured at predetermined locations within the slope. The results showed that fibre reinforcement increased the bearing resistance of the model slope significantly. For instance, inclusion of 5% waste carpet fibre increased the bearing pressure by 145% at 10% settlement ratio. / The post-print of this article will be released for public view when the version of record has been published by ASCE.

[pt] Neste trabalho o método dos elementos finitos é empregado para analisar a estabilidade de taludes em solo solapados por voçorocas. Muitos dos deslizamentos de solo que ocorrem em taludes e encostas têm sido causados pelo fenômeno de voçorocas, o resultado de um processo de erosão de solos muito complexo. Uma breve revisão sobre a formação e o crescimento de voçorocas, bem como sobre os seus efeitos na estabilidade de taludes em solo, é feita neste trabalho. Exemplos ilustrativos da aplicação desta técnica para alguns casos de taludes e encostas erodidos por voçorocas são apresentados, incluindo-se duas análises numéricas da estabilidade de encostas situadas na cidade de Goiânia - GO. Dificuldades numéricas devido à baixa taxa de convergência da solução nas proximidades do colapso do talude são também discutidas. / [en] In this work the finite element method is employed to analyze the stability of soil slopes undermined by voçorocas (gulling). Many of the shear slides occurred in both natural slopes and embankments have been caused by the phenomenon of voçorocas, the outcome of a very complex soil erosion mechanism. A brief review about the formation and growing of voçorocas, as well as an overview of their effects on soil slope stability, are made in this work. In the numerical simulation by the finite element method, the potential slip surface is identified through the progressive formation of a region of yielded soil as the erosion process advances. A simple model, consisting of incremental excavations of soil near the foot of the slope, is used in this work to represent the undermining mechanism. Illustrative examples of this technique are presented for some cases of natural soil slopes eroded by voçorocas in the city of Goiania - GO. Numerical difficulties due to the poor convergence of the solution near the soil collapse are also discussed.

[pt] Os efeitos catastróficos de terremotos que frequentemente acontecem na costa ocidental da América do Sul motivaram a realização desta pesquisa. O Equador, em particular, encontra-se localizado em uma zona de alta atividade sísmica devido a processos de subducção de placas tectônicas que originam sismos de grande magnitude, como o terremoto de magnitude Mw igual 7.8 acontecido em 16 de abril de 2016 na cidade costeira de Pedernales, que produziu grandes danos à infraestrutura e perdas de vidas humanas. A presente pesquisa tem como objetivo estudar o comportamento dinâmico de dois tipos de estruturas de terra: um talude de encosta composto de solo coluvial de altura aproximada de 70 m e a barragem de enrocamento de Mazar construída com altura de 166 m para fins de aproveitamento hidrelétrico. A barragem de Mazar, em função da sua altura, é classificada como barragem de grande tamanho pela International Commission on Large Dams (ICOLD) e qualificada pela Norma Equatoriana da Construção (NEC, 2014) como estrutura de importância essencial, com obrigatoriedade de verificação do seu desempenho sísmico para dois terremotos de projeto: o terremoto operacional base (OBE) e o máximo terremoto provável (MCE) com períodos de retorno de 475 anos e 2500 anos, respectivamente. As análises efetuadas neste trabalho incluíram a geração de sismos de projeto, investigação da estabilidade estática e pseudoestática de taludes, determinação de deslocamentos permanentes mediante métodos analíticos simplificados e simulações numéricas. Diferenças significativas nos deslocamentos permanentes máximos foram observadas empregando as abordagens analítica e numérica. / [en] The catastrophic effects of earthquakes that frequently occur on the West coast of South America motivated this research. Ecuador, in particular, is located in a zone of high seismic activity due to processes of tectonic plate subduction that give rise to earthquakes of great magnitude, such as the seismic motion of magnitude Mw equal 7.8 that struck the coastal city of Pedernales on April 16 2016, producing great damages to the infrastructure and losses of human lives. The present research aims to study the dynamic behavior of two types of earth structures: a slope composed of colluvial soil of approximately 70 m height and the Mazar rockfill dam constructed for hydroelectric generation. The Mazar dam, according to its height (166 m), is classified as a large dam by the International Commission on Large Dams (ICOLD) and qualified by the Ecuadorian Construction Standard (NEC, 2014) as a structure of essential importance, with mandatory analysis of seismic performance under two seismic design ground motions: the operating basis earthquake (OBE) and the maximum credible earthquake (MCE) with return periods of 475 years and 2500 years, respectively. The analyses carried out in this work included the generation of the OBE and MCE earthquakes, investigation of static and pseudo static stability of slopes, determination of permanent displacements using simplified analytical methods and numerical simulations. Significant differences in the maximum permanent displacements were observed using analytical and numerical approaches.