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Suscetibilidade à ocorrência de escorregamentos nas vertentes do limite Norte do Concelho de Almada utilizando métodos de base física
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No presente trabalho aborda-se a determinação da suscetibilidade à ocorrência de movimentos de vertente nas bacias hidrográficas do limite Norte do Concelho de Almada, desde a ponte 25 de abril até à região da Trafaria. Para tal, recorreu-se à aplicação de métodos de base física, recorrendo ao módulo hidrológico do SHALSTAB para a determinação do nível piezométrico em cenários de precipitação intensa e ao modelo do talude infinito de análise da estabilidade de vertentes de equilíbrio limite. Para a aplicação do modelo tomou-se como base um inventário de movimentos em vertente realizado anteriormente, onde foram cartografados 183 movimentos. Para determinar os limiares críticos de precipitação, para os quais é excedida a quantidade de precipitação necessária para a ocorrência de movimentos de vertente, procedeu-se à recolha de dados de precipitações diárias referentes a um período temporal de 32 anos (1985-2017), que foram devidamente tratados e analisados a fim de se obter o valor de precipitação efetiva a ser aplicado no módulo hidrológico do SHALSTAB. Posteriormente, procedeu-se à obtenção e determinação das variáveis base fulcrais à aplicação do modelo. Deste modo, realizou-se um mapa de declives para a área de estudo através da criação de um MDT (Modelo Digital de Terreno) e recolheu-se informação referente aos parâmetros geotécnicos do solo como pesos volúmicos e permeabilidade, que foram obtidos por pesquisa bibliográfica, e coesão e ângulo de atrito interno efetivos, que foram obtidos por pesquisa bibliográfica e calibrados através de um processo de retroanálise. Estimou-se também a espessura de solo potencialmente instável, deduzida através de três modelos de determinação deste parâmetro, assim como, a espessura de solo saturado obtida pelo módulo hidrológico do SHALSTAB. Após a construção dos modelos de base física, realizou-se a respetiva validação por comparação com os movimentos registados no inventário, através da construção de curvas ROC (Receiver Operating Characteristic) e do cálculo da respetiva Área Abaixo da Curva (AAC), que permitiram verificar a qualidade dos modelos de previsão dos movimentos de massa de vertente, com o melhor modelo a atingir valor de AAC de 0,76, ou seja um modelo aceitável.
This work approaches the susceptibility assessment to the occurrence of slope mass movements in the hydrographic basins of the Northern border of the Almada County, from the bridge 25 of April all the way to the Trafaria region. It was applied a physically based model using the hydrological module of SHALSTAB for piezometric level determination in scenarios of intense precipitation and the limit equilibrium model of the infinite slope stability analysis. For the application of the model, an inventory of 183 slope movements which was acquired in previous studies in the study zone, was used as a base. To determine the critical precipitation thresholds for which the amount of precipitation tends to trigger the occurrence of slope movements is exceeded, was also collected daily precipitation data for a 32-year period (1985-2017), which was treated and analyzed. Subsequently, the base variables were obtained and determined to the application of the model. A slope angle map was created for the study area by means of an DTM (Digital Terrain Model) and information on soil geotechnical parameters was collected, such as soils unit weights and saturated permeability, which were obtained by bibliographical research and effective cohesion and effective internal friction angle, from bibliography and then later calibrated through a process of retro-analysis of the landslides included in the inventory. It was also estimated the potentially unstable soil’s thickness, deduced by the application of three different models, and the saturated soil thickness obtained through the hydrological module SHALSTAB. The physically based models produced were object of validation by comparison with the landslides recorded in the inventory, through the construction of ROC (Receiver Operating Characteristic) curves and the calculation of the Area Under a Curve (AUC), which allowed the assessment of the performance of the model produced at predicting landslide occurrence, with the best model providing an acceptable result of AUC of 0.76.
This work approaches the susceptibility assessment to the occurrence of slope mass movements in the hydrographic basins of the Northern border of the Almada County, from the bridge 25 of April all the way to the Trafaria region. It was applied a physically based model using the hydrological module of SHALSTAB for piezometric level determination in scenarios of intense precipitation and the limit equilibrium model of the infinite slope stability analysis. For the application of the model, an inventory of 183 slope movements which was acquired in previous studies in the study zone, was used as a base. To determine the critical precipitation thresholds for which the amount of precipitation tends to trigger the occurrence of slope movements is exceeded, was also collected daily precipitation data for a 32-year period (1985-2017), which was treated and analyzed. Subsequently, the base variables were obtained and determined to the application of the model. A slope angle map was created for the study area by means of an DTM (Digital Terrain Model) and information on soil geotechnical parameters was collected, such as soils unit weights and saturated permeability, which were obtained by bibliographical research and effective cohesion and effective internal friction angle, from bibliography and then later calibrated through a process of retro-analysis of the landslides included in the inventory. It was also estimated the potentially unstable soil’s thickness, deduced by the application of three different models, and the saturated soil thickness obtained through the hydrological module SHALSTAB. The physically based models produced were object of validation by comparison with the landslides recorded in the inventory, through the construction of ROC (Receiver Operating Characteristic) curves and the calculation of the Area Under a Curve (AUC), which allowed the assessment of the performance of the model produced at predicting landslide occurrence, with the best model providing an acceptable result of AUC of 0.76.
Descrição
Trabalho de projecto de mestrado, Geologia Aplicada (Geologia de Engenharia) Universidade de Lisboa, Faculdade de Ciências, 2018
Palavras-chave
Movimentos de vertente Suscetibilidade Concelho de Almada Limiares de precipitação Modelo de base física SHALSTAB Trabalhos de projeto de mestrado - 2018