Comparação entre os modelos SHALSTAB e SINMAP no estudo de áreas susceptíveis a escorregamentos em São Sebastião - SP
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2018-03-17
Autores
Sisto, Felipe Pereira de [UNESP]
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Universidade Estadual Paulista (Unesp)
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Os estudos ambientais com intuito de avaliar a susceptibilidade de áreas quanto à ocorrência de processos geológicos, como os escorregamentos, vêm tendo cada vez mais espaço e importância, conforme novas metodologias e tecnologias, capazes de prevê-los, vão surgindo. O litoral norte do Estado de São Paulo, onde se localiza o município de São Sebastião, é uma das regiões mais afetadas por escorregamentos no país, devido a fatores naturais como altas declividades e índices pluviométricos elevados, aliado a uma ocupação desordenada de suas encostas, fruto da falta de planejamento urbano. No presente trabalho foram realizadas simulações através dos modelos de estabilidade de taludes, SHALSTAB (Shallow Landsliding Stability Model) e SINMAP (Stability Index Mapping), em diversos cenários distintos, para avaliar e comparar os resultados obtidos de acordo com a metodologia da razão entre o Índice de Acerto (IA) e Índice de Acerto e (IE). Para tal, foi elaborado um mapa geológico, pelo compilado de dados de outros autores, e mapas auxiliares, como o MDT, hipsométrico, de declividade e um inventário das cicatrizes de escorregamentos, necessários nas etapas de compartimentação fisiográfica e de modelagem. Na etapa de compartimentação fisiográfica, foram definidas feições de terreno mais importantes no estudo dos escorregamentos e baseando-se nelas, a área de estudo foi dividida em unidades fisiográficas. Depois de uma avaliação de susceptibilidade nas unidades fisiográficas, algumas se apresentaram mais propícias ao desenvolvimento dos escorregamentos. Dentre essas, as unidades III e IV, se destacaram, principalmente por apresentar número muito superior de cicatrizes de escorregamento, e nelas foram escolhidas algumas bacias hidrográficas como áreas alvo para a aplicação dos modelos SHALSTAB e SINMAP. Os trabalhos de campo, com foco nestas áreas, contaram com 58 pontos de visitação, onde foi possível obter dados quanto a espessura dos perfis de alteração e realização de coleta de material para ensaios geotécnicos em laboratório. Os ensaios geotécnicos de índices físicos possibilitaram a obtenção de parâmetros de entrada necessários para aplicação dos modelos SHALSTAB e SINMAP. Os modelos, no geral, conseguiram prever de maneira satisfatória as áreas instáveis da área de estudo, mostrando a correlação entre essas e as cicatrizes de escorregamentos mapeadas. Na comparação entre os modelos pela razão IA/IE, observou-se que os valores de IA e IE foram maiores no SINMAP, devido ao próprio funcionamento do modelo. Os valores da razão, no entanto, foram semelhantes, com uma pequena vantagem para o SHALSTAB, indicando que na metodologia aplicada, o modelo conseguiu simular as áreas instáveis de modo mais satisfatório que o SINMAP.
Environmental studies with the purpose of evaluating the susceptibility of areas related to the occurrence of geological processes, such as landslides, are becoming more and more important, as new methodologies and technologies capable of predicting such processes are emerging. The northern coast of the State of São Paulo, where the municipality of São Sebastião is located, is one of the most affected regions by landslides in the country, due to natural factors such as high slopes and high rainfall levels, together with a disorderly occupation of its slopes, due to the lack of urban planning. In the present work, simulations were performed through the slope stability models, SHALSTAB and SINMAP, in several different scenarios, in order to evaluate and compare the results obtained according to the methodology of the ratio between the Success Index (SI) and Error Index (EI). For this, a geological map was made through the compilation of data from other authors, and auxiliary maps, such as the MDT, hypsometric, slope and an inventory of the landslides scars, required in the physiographic compartmentalization and modeling stages. In the physiographic compartmentalization stage, more important terrain features in the study of landslides were defined and based on them, the study area was divided into physiographic units. After an evaluation of susceptibility of the physiographic units, some were more propitious to the development of landslides. Among these, units III and IV, stood out, mainly because they presented a much higher number of sliding scars, and in them, some watersheds were chosen as target areas for the application of the SHALSTAB and SINMAP models. Fieldwork focused on these areas was made, with a total of 58 points of visitation, where it was possible to obtain data on the thickness of the alteration profiles, and the collection of material for geotechnical tests in the laboratory. The geotechnical tests of physical indexes allowed to obtain the necessary input parameters for the SHALSTAB and SINMAP models. The models, in general, were able to predict satisfactorily the unstable regions of the study area, showing the correlation between these and the landslides scars. In the comparison between the models using the SI/EI ratio, it was observed that the SI and EI values were higher in the SINMAP, due to the model's own functioning. The values of the ratio, however, were similar, with a small advantage for SHALSTAB, indicating that in the applied methodology, the model was able to simulate unstable areas more satisfactorily than SINMAP.
Environmental studies with the purpose of evaluating the susceptibility of areas related to the occurrence of geological processes, such as landslides, are becoming more and more important, as new methodologies and technologies capable of predicting such processes are emerging. The northern coast of the State of São Paulo, where the municipality of São Sebastião is located, is one of the most affected regions by landslides in the country, due to natural factors such as high slopes and high rainfall levels, together with a disorderly occupation of its slopes, due to the lack of urban planning. In the present work, simulations were performed through the slope stability models, SHALSTAB and SINMAP, in several different scenarios, in order to evaluate and compare the results obtained according to the methodology of the ratio between the Success Index (SI) and Error Index (EI). For this, a geological map was made through the compilation of data from other authors, and auxiliary maps, such as the MDT, hypsometric, slope and an inventory of the landslides scars, required in the physiographic compartmentalization and modeling stages. In the physiographic compartmentalization stage, more important terrain features in the study of landslides were defined and based on them, the study area was divided into physiographic units. After an evaluation of susceptibility of the physiographic units, some were more propitious to the development of landslides. Among these, units III and IV, stood out, mainly because they presented a much higher number of sliding scars, and in them, some watersheds were chosen as target areas for the application of the SHALSTAB and SINMAP models. Fieldwork focused on these areas was made, with a total of 58 points of visitation, where it was possible to obtain data on the thickness of the alteration profiles, and the collection of material for geotechnical tests in the laboratory. The geotechnical tests of physical indexes allowed to obtain the necessary input parameters for the SHALSTAB and SINMAP models. The models, in general, were able to predict satisfactorily the unstable regions of the study area, showing the correlation between these and the landslides scars. In the comparison between the models using the SI/EI ratio, it was observed that the SI and EI values were higher in the SINMAP, due to the model's own functioning. The values of the ratio, however, were similar, with a small advantage for SHALSTAB, indicating that in the applied methodology, the model was able to simulate unstable areas more satisfactorily than SINMAP.
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Palavras-chave
Serra do Mar, Escorregamentos, SHALSTAB, SINMAP, Landslides