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Estudo de solo de alteração do Jurássico superior: caracterização geotécnica e melhoramento por cal e cimento
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Esta dissertação foi desenvolvida com o objetivo de realizar caracterização geotécnica de solos de alteração superficial do Jurássico superior da formação J3so – Margas, argilas e grés de Sobral (Kimeridgiano superior – Titoniano), que forma parte das arribas costeiras da região a sul do Forte do Pai Mogo, na zona norte do conselho da Lourinhã, e analisar os possíveis efeitos de melhoramento destes solos pela adição de cal e de cimento. Estes solos, que ocorrem em grandes extensões na região envolvente, têm comportamento geotécnico muito deficiente, sendo particularmente sensíveis à erosão superficial pelas águas pluviais e à ocorrência de movimentos de massa de vertente geralmente de tipo superficial, mas com impacte significativo em estruturas e actividades humanas. Foram colhidas sete amostras nas arribas a sul do Forte do Pai Mogo sobre as quais foram realizados ensaios de identificação que incluíram os limites de liquidez, plasticidade e retracção, ensaio de Expansibilidade LNEC, com o objetivo de selecionar a amostra com melhores condições para a aplicação dos melhoramentos por adição de cal e cimento em percentagens de 2 e 5%. Para se realizarem as técnicas de melhoramento foi seleccionada a amostra com as características geotécnicas mais desfavoráveis, a amostra L1, que foi objecto de ensaios de expansibilidade em edómetro e ensaios de corte directo, em condições próximas de situação consolidada e drenada. Este solo corresponde a uma argila magra (CL) na classificação USCS e a um solo argiloso (A6) na classificação AASHTO, obtendo-se um índice de plasticidade de 15. A resistência ao corte em ensaios de corte directo forneceu valores de coesão de 9.43 kPa e ângulo de atrito interno de 23º. Após a realização dos tratamentos de cal e cimento, nas percentagens de 2% e 5%, observou-se que o tratamento com melhores resultados é o da adição de cimento em 5%. Verificando-se melhorias significativas expressas na redução do índice de plasticidade para valores de 8.2%, na alteração da classificação para silte (ML) na classificação USCS e para solo siltoso (A4) na classificação AASHTO, e pelo acréscimo do ângulo de atrito interno para 52.62º e um decréscimo da coesão de 0kPa, determinados em ensaios de corte directo. Pode-se então concluir que o tratamento com 5% de cimento é, neste caso, uma possível solução para prevenção da instabilidade. Contudo, seria interessante a realização de ensaios in situ de modo a validar os resultados obtidos em laboratório, verificar a eficiência de tratamentos combinados de cal e cimento e verificar a durabilidade dos tratamentos face às condições ambientais existentes no terreno.
This study has been developed with the aim to perform a geotechnical characterization superficial weathered soils, from upper Jurassic, J3so – Margas, argilas e grés de Sobral (upper Kimmeridgian – Tithonian). Seven samples were collected in the sea cliff exposures located to south of Forte do Pai Mogo, in the northern area of Lourinhã county. The essential aims of this work were: the laboratory study of the soil samples geotechnical properties, and the assessment of the geotechnical properties modifications introduced by the addition of 2% and 5% cement or lime treatment to the samples. These soils, which cover large areas, have a poor geotechnical behaviour, being particularly susceptible to surficial erosion by rainfall and surface water runoff, and also to the occurrence of mainly shallow slope mass movements which have a significant impact of structures and human activities. The samples were object of liquid, plastic and shrinkage limits testing, and also free swell LNEC tests, with the aim of selecting the sample with the poorer geotechnical properties to perform further geotechnical testing. Subsequently, this sample was used to test effects of the improvement techniques, which consist in the addiction of cement and lime in the percentages of 2% and 5%. In order to apply the techniques of improvement was selected the sample with the poorer geotechnical characteristics, which was sample L1. This sample was classified as lean clay (CL) in USCS classification and clayey soil (A6) in AASHTO classification. The plasticity index was 15.3% and the direct shear testing provide values of cohesion of 9.43kPa and internal friction angle of 23º. After the realization of the improvements whit lime and cement, in the above-mentioned percentages, was observed that the improvement with the 5% cement treatment resulted in better geotechnical characteristics. The beneficial results were noticed in the reduced plasticity index with values of 8.2%, the change of USCS classification to silt (ML) and in the AASHTO classification to silty soil, and for the decrease of cohesion to 0kPa and the increase of the internal friction angle to 52.62º, recorded in the direct shear test. Has been concluded that the treatment with 5% of cement is, in this case, one possible solution to prevent the soil instability. However, it will be interesting to do in situ tests to validate the results that were obtained in the laboratory conditions, to test the efficiency of treatments using combinations of cement and lime, and also to test the long term durability of these treatments under the environmental conditions prevailing I the study area.
This study has been developed with the aim to perform a geotechnical characterization superficial weathered soils, from upper Jurassic, J3so – Margas, argilas e grés de Sobral (upper Kimmeridgian – Tithonian). Seven samples were collected in the sea cliff exposures located to south of Forte do Pai Mogo, in the northern area of Lourinhã county. The essential aims of this work were: the laboratory study of the soil samples geotechnical properties, and the assessment of the geotechnical properties modifications introduced by the addition of 2% and 5% cement or lime treatment to the samples. These soils, which cover large areas, have a poor geotechnical behaviour, being particularly susceptible to surficial erosion by rainfall and surface water runoff, and also to the occurrence of mainly shallow slope mass movements which have a significant impact of structures and human activities. The samples were object of liquid, plastic and shrinkage limits testing, and also free swell LNEC tests, with the aim of selecting the sample with the poorer geotechnical properties to perform further geotechnical testing. Subsequently, this sample was used to test effects of the improvement techniques, which consist in the addiction of cement and lime in the percentages of 2% and 5%. In order to apply the techniques of improvement was selected the sample with the poorer geotechnical characteristics, which was sample L1. This sample was classified as lean clay (CL) in USCS classification and clayey soil (A6) in AASHTO classification. The plasticity index was 15.3% and the direct shear testing provide values of cohesion of 9.43kPa and internal friction angle of 23º. After the realization of the improvements whit lime and cement, in the above-mentioned percentages, was observed that the improvement with the 5% cement treatment resulted in better geotechnical characteristics. The beneficial results were noticed in the reduced plasticity index with values of 8.2%, the change of USCS classification to silt (ML) and in the AASHTO classification to silty soil, and for the decrease of cohesion to 0kPa and the increase of the internal friction angle to 52.62º, recorded in the direct shear test. Has been concluded that the treatment with 5% of cement is, in this case, one possible solution to prevent the soil instability. However, it will be interesting to do in situ tests to validate the results that were obtained in the laboratory conditions, to test the efficiency of treatments using combinations of cement and lime, and also to test the long term durability of these treatments under the environmental conditions prevailing I the study area.
Descrição
Trabalho de projecto de mestrado, Geologia aplicada (Geologia de engenharia), Universidade de Lisboa, Faculdade de Ciências, 2015
Palavras-chave
Argilas Solo de alteração Cimento Cal Geotécnia Forte do Pai Mogo Trabalhos de projecto de mestrado - 2015