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Abstract(s)
A presente dissertação insere-se na análise da estabilidade de taludes, com âmbito no estudo do comportamento de taludes em areia quando imersos em escoamentos fluviais.
As margens dos rios estão sujeitas a instabilidades associadas à modificação contínua das suas características físicas, em particular a sua geometria, devido à ação do escoamento. Os fenómenos que tipicamente causam instabilidade de taludes imersos são a diminuição da cota do leito e a erosão lateral. Apesar do conhecimento que se tem hoje sobre os processos de erosão lateral e de instabilidade dos taludes, geralmente a interação entre os referidos processos não é considerada na análise da estabilidade das margens dos leitos aluvionares sujeitos a forças hidrodinâmicas que resultam do escoamento de cheias. O escoamento da água atua como tensão tangencial nas suas fronteiras, o que pode alterar as tensões efetivas no solo. Consequentemente, a rotura pode ocorrer por redução da resistência ao corte do solo ou por aumento das forças instabilizadoras ou ambos.
Neste contexto, a presente dissertação pretende contribuir para melhorar o conhecimento sobre a interação entre os processos de erosão lateral e de instabilidade dos taludes e definir a condição de carga apropriada a incluir na análise da estabilidade dos taludes em areia imersos em escoamento fluvial.
Para concretizar o objetivo, foi realizada uma análise determinística complementada por modelação física do talude, em escala reduzida. Nos ensaios laboratoriais mediram-se campos de velocidades instantâneas recorrendo ao sistema de medição não intrusiva Particle Image Velocimetry (PIV).
De um modo geral, os resultados mostram que a ação do escoamento da água origina erosão lateral, o que aumenta a largura do leito, com o inerente aumento da inclinação do talude, o que diminui a sua estabilidade. A abordagem adotada para o cálculo da estabilidade dos taludes submersos tem em conta as alterações da sua geometria devido à erosão lateral, o que representa uma melhoria importante para a previsão da geometria que conduz à instabilidade do talude, que encontra aplicações em situações como a dragagem controlada de sedimentos e a análise de risco de instabilidade dos taludes associado ao escoamento de cheias.
This work is on the slope stability analysis, with scope in the study of the behavior of sandy slopes when immersed in river flows. The riverbanks are subjected to instabilities associated with continuous modification of their physical characteristics, in particular its geometry, in consequence of river flow. The phenomena that most commonly cause bank instability are bed degradation and lateral erosion. While understanding of both bank erosion and slope failure processes has improved in recent years, the interaction between these two processes is not usually considered in the context of sand-bed rivers subjected to hydrodynamic forces that arise from currents of the flood events. Currents act as tangential stress on its boundaries which can alter the effective overburden stress in soil mass. Failure can occur by reduction of the shear strength of the soil which decreases the resisting forces in the slope or by the increase of the driving forces in the slope or both. In this context, the present work intends to contribute to improve the knowledge of the interaction between bank erosion and slope failure processes and set the appropriate loading condition to include in stability analysis of submerged sandy slopes. To achieve the proposed objective, a deterministic analysis complemented by physical modeling of the slope was performed. In the laboratory tests, the measurement of instantaneous velocity fields was made using the non-intrusive technique Particle Image Velocimetry (PIV). In general, the results show that the action of the river flow originates lateral erosion, which increases the bed width and results in steepening of the slope, which reduces its stability. The approach adopted for computing the stability of submerged slopes takes into account the changes of its geometry due to lateral erosion prior to mass failure, which represents a major improvement to the prediction of geometry that leads to instability of the slope, which finds applications in situations such as dredging of sediments and risk analysis of slope instability associated with the flow of flooding.
This work is on the slope stability analysis, with scope in the study of the behavior of sandy slopes when immersed in river flows. The riverbanks are subjected to instabilities associated with continuous modification of their physical characteristics, in particular its geometry, in consequence of river flow. The phenomena that most commonly cause bank instability are bed degradation and lateral erosion. While understanding of both bank erosion and slope failure processes has improved in recent years, the interaction between these two processes is not usually considered in the context of sand-bed rivers subjected to hydrodynamic forces that arise from currents of the flood events. Currents act as tangential stress on its boundaries which can alter the effective overburden stress in soil mass. Failure can occur by reduction of the shear strength of the soil which decreases the resisting forces in the slope or by the increase of the driving forces in the slope or both. In this context, the present work intends to contribute to improve the knowledge of the interaction between bank erosion and slope failure processes and set the appropriate loading condition to include in stability analysis of submerged sandy slopes. To achieve the proposed objective, a deterministic analysis complemented by physical modeling of the slope was performed. In the laboratory tests, the measurement of instantaneous velocity fields was made using the non-intrusive technique Particle Image Velocimetry (PIV). In general, the results show that the action of the river flow originates lateral erosion, which increases the bed width and results in steepening of the slope, which reduces its stability. The approach adopted for computing the stability of submerged slopes takes into account the changes of its geometry due to lateral erosion prior to mass failure, which represents a major improvement to the prediction of geometry that leads to instability of the slope, which finds applications in situations such as dredging of sediments and risk analysis of slope instability associated with the flow of flooding.
Description
Keywords
Análise Determinística Erosão Escoamento Fluvial Estabilidade de Taludes Modelação Física