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Avaliação da susceptibilidade à ocorrência de movimentos de massa em vertentes na Freguesia de Santa Maria Maior, Lisboa: levantamento e avaliação de locais susceptíveis e medidas de mitigação
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O presente trabalho tem por objectivos a determinação da susceptibilidade de movimentos de massa em vertente através da aplicação de métodos de base física, o levantamento e avaliação de zonas susceptíveis e a apresentação de medidas de mitigação, em contexto urbano, para um caso de estudo representado pela freguesia de Santa Maria Maior, Lisboa. Para a avaliação da susceptibilidade à ocorrência de movimentos de massa em vertentes aplicaram-se dois modelos, o modelo SHALSTAB de Montgomery e Dietrich (1994) e o modelo do Talude Infinito de Sharma (2002). O primeiro modelo permite a determinação da razão entre a espessura de solo saturado e a espessura de solo potencialmente instável, a qual é variável de entrada no modelo de Sharma (2002). O modelo do Talude Infinito permite a determinação quantitativa da estabilidade das vertentes pela aplicação do método do equilíbrio limite, o qual simula os mecanismos físicos que condicionam a ocorrência destes movimentos superficiais. Como resultado final obtém-se dados de factor de segurança, o qual pode ser representado por classes de susceptibilidade. No final, é necessário proceder à validação do modelo, por comparação com inventários de movimentos, e à avaliação da sua capacidade de previsão. Os dados de entrada dos modelos, dados geotécnicos, geológicos, hidrogeológicos, geomorfológicos e de precipitação, foram obtidos através da consulta de relatórios geológicos/ geotécnicos, hidrogeológicos e em dados publicados. Estes foram sujeitos a vários processos de análise, organização, correlação e retroanálise de modo a obter os valores que melhor descrevem as características das formações geológicas. Ademais, procedeu-se à representação de algumas características da freguesia, as quais permitem conhecer melhor o substrato geológico, o seu comportamento e reconhecer a presença de água. A campanha de campo realizada teve como objectivo a avaliação das características do edificado presente nas zonas já anteriormente classificadas como susceptíveis. Com estes dados pretende-se inferir se existe uma relação entre as patologias identificadas no edificado e a ocorrência de instabilidade de solos, para que depois sejam propostas várias medidas de mitigação. Com este trabalho foi possível comprovar que os modelos utilizados podem ser aplicados a zonas urbanizadas, tendo apresentado uma capacidade de previsão aceitável, com valor de AAC de 0,8. O mapa de susceptibilidade permite evidenciar algumas zonas com susceptibilidade elevadas, estando estas concentradas, em maior quantidade, na colina do Castelo e em torno da colina de São Roque. Correlacionando estas conclusões com os dados da campanha de campo, pode considerar-se que este tipo de análise do edificado permite inferir a ocorrência de instabilidade, sendo uma mais valia neste tipo de avaliações.
The present work has as main goals the determination of the susceptibility of landslides through the application of physical based methods, the identification and evaluation of susceptible areas and the presentation of mitigation measures, at an urban context, represented by the parish of Santa Maria Maior, Lisbon case study. To evaluate the susceptibility of the occurrence of landslides, two models were applied, the hydrological model, SHALSTAB by Montgomery and Dietrich (1994), and the geological model of “Infinite Slope” Sharma's (2002). The first model allows the determination of the ratio between the thickness of saturated soil and the thickness of potentially unstable soil, which is an input variable in the geological model. The geological model allows the quantitative determination of the slope stability by applying the limit equilibrium method, which simulates the physical mechanisms that condition the occurrence of surface movements. As a final result, safety factor data are obtained, which can be reclassified to represent susceptibility classes. In the end, it is necessary to proceed with the validation of the model by comparison with movement inventories and the evaluation of its prediction capacity. The input data of the models, geotechnical, geological, hydrogeological, geomorphological and precipitation data, were obtained by analysis of geological/ geotechnical and hydrogeological reports and published data. These went through several processes of analysis, organization, correlation and back analysis in order to obtain the values that best describe the characteristics of the geological formations. In addition, some characteristics of the parish were represented, which allow a better understanding of the geological subtract, its behaviour and the presence of water. The field work consisted of assessing the characteristics of the building present in areas previously classified as susceptible. With these data it is intended to infer whether there is a relationship between the pathologies identified in the building and the occurrence of soil instability. So that several risk mitigation measures are then proposed. With this work it was possible to prove that the models used can be applied to urbanized areas, having an acceptable forecasting capacity, with AAC value of 0,8. The susceptibility map allows evidence of some areas with high susceptibility, which are concentrated, in greater quantity, on the hill of Castelo and around the hill of São Roque. Correlating these conclusions with the data from the field work, it is possible to consider that this type of analysis of the building allows to infer the occurrence of instability, being an asset in this type of evaluations.
The present work has as main goals the determination of the susceptibility of landslides through the application of physical based methods, the identification and evaluation of susceptible areas and the presentation of mitigation measures, at an urban context, represented by the parish of Santa Maria Maior, Lisbon case study. To evaluate the susceptibility of the occurrence of landslides, two models were applied, the hydrological model, SHALSTAB by Montgomery and Dietrich (1994), and the geological model of “Infinite Slope” Sharma's (2002). The first model allows the determination of the ratio between the thickness of saturated soil and the thickness of potentially unstable soil, which is an input variable in the geological model. The geological model allows the quantitative determination of the slope stability by applying the limit equilibrium method, which simulates the physical mechanisms that condition the occurrence of surface movements. As a final result, safety factor data are obtained, which can be reclassified to represent susceptibility classes. In the end, it is necessary to proceed with the validation of the model by comparison with movement inventories and the evaluation of its prediction capacity. The input data of the models, geotechnical, geological, hydrogeological, geomorphological and precipitation data, were obtained by analysis of geological/ geotechnical and hydrogeological reports and published data. These went through several processes of analysis, organization, correlation and back analysis in order to obtain the values that best describe the characteristics of the geological formations. In addition, some characteristics of the parish were represented, which allow a better understanding of the geological subtract, its behaviour and the presence of water. The field work consisted of assessing the characteristics of the building present in areas previously classified as susceptible. With these data it is intended to infer whether there is a relationship between the pathologies identified in the building and the occurrence of soil instability. So that several risk mitigation measures are then proposed. With this work it was possible to prove that the models used can be applied to urbanized areas, having an acceptable forecasting capacity, with AAC value of 0,8. The susceptibility map allows evidence of some areas with high susceptibility, which are concentrated, in greater quantity, on the hill of Castelo and around the hill of São Roque. Correlating these conclusions with the data from the field work, it is possible to consider that this type of analysis of the building allows to infer the occurrence of instability, being an asset in this type of evaluations.
Descrição
Relatório de Estágio de Mestrado em Geologia do Ambiente, Riscos Geológicos e Ordenamento do Território, Faculdade de Ciências, Universidade de Lisboa, 2021
Palavras-chave
Movimentos de vertente Susceptibilidade Talude infinito Edificado e patologias estruturais Mitigação Teses de mestrado - 2021