Estudo da resistência e da deformabilidade de um perfil de solo tropical não saturado
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Data
2022-02-04
Autores
Fernandes, Jeferson Brito
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Editor
Universidade Estadual Paulista (Unesp)
Resumo
Solos encontrados em regiões de clima tropical ou solos de origem tropical são caracterizados por particularidades no comportamento mecânico ainda não equacionadas. Esses solos podem ser encontrados com grande facilidade no Brasil devido às altas taxas pluviométricas e intensa atuação de processos físico-químicos sobre o território. A existência de diferentes graus de evolução ao longo desses perfis é comum e isso tem levado a inconsistências durante a aplicação de modelos para previsão do comportamento mecânico. Atualmente, o desafio tem sido definir funções com variáveis que representem o comportamento mecânico desses solos. Nesse sentido, essa pesquisa tem como objetivo avançar nesse conhecimento a partir do estudo do comportamento de um perfil de solo de origem tropical não saturado. O perfil estudado é formado por solos de origem coluvionar com diferentes graus de evolução ao longo da profundidade. Estudos prévios mostram que as maiores variações de umidade ocorrem na zona ativa do perfil, entre 4,0 e 5,0m de profundidade. Foram estudados parâmetros de resistência e deformabilidade em função das variáveis de tensão, propriedades físicas, evolução e gênese. Esses parâmetros foram obtidos a partir de ensaios triaxiais saturados e não saturados, com bender elements e medidores de deslocamento vertical e radial internos. Os ensaios de laboratório foram realizados em amostras indeformadas coletadas entre 1,5 e 16,0m de profundidade. Os resultados dos ensaios de laboratório demonstram que o comportamento mecânico desses solos é muito afetado pela sucção, em especial para os solos abaixo da zona ativa. O ângulo de atrito interno médio (fi) é de 30º, sendo pouco afetado pela sucção e características do solo ao longo do perfil. A taxa de variação do intercepto de coesão em função da sucção (fi_b) foi crescente ao longo perfil, e mais intensa abaixo da zona ativa. A taxa de variação do módulo de cisalhamento máximo (G0) com a sucção variou mais intensamente para valores mais baixos de sucção. Os solos abaixo da zona ativa mostraram maior acréscimo em G0 para uma mesma variação da sucção. Os parâmetros de ajuste de um modelo empírico da curva de degradação do módulo mostraram que existe uma relação que se mantém constante ao longo do perfil. Essa relação foi denominada de constante do material (κ) e constatou-se por meio da comparação dos resultados obtidos com aqueles disponíveis na literatura que os valores de κ são maiores para solos mais finos. O aprimoramento do modelo empírico utilizado para ajuste das curvas de degradação também incluiu uma relação com o índice de vazios, que foi linear para os solos estudados. A integração dos resultados de ensaios de laboratório obtidos nesta pesquisa com resultados de ensaios de campo disponíveis na literatura possibilitou uma melhor compreensão dos fatores que afetam a resistência e a deformabilidade desses solos. Nesse sentido, verificou-se que existe uma boa relação entre G0 obtido a partir de bender elements e pelo ensaio de dilatômetro sísmico. Além disso, foi verificado que a relação G0/qmax é maior para os solos superficiais, assim como a relação G0/qc. Isso indica que os solos desta parte do perfil são de fato mais evoluídos com presença de cimentação. Os resultados obtidos nesta pesquisa ampliam o banco de dados de parâmetros geotécnicos do perfil de solo estudado, contribuindo para a integração entre os resultados de ensaios de campo e laboratório de um perfil de solo não saturado de origem tropical.
Soils found in tropical climatic regions or soils of tropical origin are distinguished by particularities in their mechanical behavior that have not yet been resolved. These soils can be frequently found in Brazil due to the high rainfall rates and intense action of physical- chemical processes over the territory. The occurrence of different degrees of evolution along these profiles is common and it has led to inconsistencies during the application of models for predicting the mechanical behavior. Currently, the challenge has been to define functions with variables that describe the mechanical behavior of these soils. In this sense, this research aims to advance this knowledge by studying the behavior of an unsaturated tropical soil profile. The studied profile is constituted by soils of colluvial origin with different degrees of evolution along depth. Previous studies show that the greatest variations in moisture content occur in the active zone of the profile, between 4.0 and 5.0 m depth. The strength and deformability parameters as a function of stress variables, physical properties, evolution, and genesis were studied. These parameters were obtained from saturated and unsaturated triaxial tests, with bender elements and internal vertical and radial displacement meters. The laboratory tests were performed on undisturbed samples collected between 1.5 and 16.0 m depth. The average internal friction angle ( ) is 30º, little affected by suction and soil characteristics along the profile. The variation rate of the cohesion intercept as a function of suction (( b) was increased along the profile, and more intense below the active zone. The rate of variation of the maximum shear modulus (G0) with suction varied more intensely for lower suction values. Soils below the active zone showed a greater increase in G0 for the same variation in suction. The fitting parameters of an empirical model for the modulus degradation curve showed that there is a relationship that remains constant along the profile. This relationship was called material constant (κ) and it was found by comparing the results obtained with those available in the literature that the values of κ are higher for finer soils. The improvement of the empirical model used for fitting the degradation curves also included a relationship with the void ratio, which was linear for the soils studied. The integration of the laboratory test data obtained in this research with the in-situ test data available in the literature allowed for a better understanding of the factors that affect the strength and deformability of these soils. In this sense, it was found that there is a good relationship between G0 obtained from bender elements and by the seismic dilatometer test. In addition, it was found that the G0/qmax ratio is higher for the upper soil layer, as well as the G0/qc ratio. It indicates that this part of the soil profile is indeed more developed with presence of cementation. The results obtained in this research enlarge the database of geotechnical parameters for the studied soil profile, contributing to the integration between field and laboratory test results for an unsaturated soil profile of tropical origin.
Soils found in tropical climatic regions or soils of tropical origin are distinguished by particularities in their mechanical behavior that have not yet been resolved. These soils can be frequently found in Brazil due to the high rainfall rates and intense action of physical- chemical processes over the territory. The occurrence of different degrees of evolution along these profiles is common and it has led to inconsistencies during the application of models for predicting the mechanical behavior. Currently, the challenge has been to define functions with variables that describe the mechanical behavior of these soils. In this sense, this research aims to advance this knowledge by studying the behavior of an unsaturated tropical soil profile. The studied profile is constituted by soils of colluvial origin with different degrees of evolution along depth. Previous studies show that the greatest variations in moisture content occur in the active zone of the profile, between 4.0 and 5.0 m depth. The strength and deformability parameters as a function of stress variables, physical properties, evolution, and genesis were studied. These parameters were obtained from saturated and unsaturated triaxial tests, with bender elements and internal vertical and radial displacement meters. The laboratory tests were performed on undisturbed samples collected between 1.5 and 16.0 m depth. The average internal friction angle ( ) is 30º, little affected by suction and soil characteristics along the profile. The variation rate of the cohesion intercept as a function of suction (( b) was increased along the profile, and more intense below the active zone. The rate of variation of the maximum shear modulus (G0) with suction varied more intensely for lower suction values. Soils below the active zone showed a greater increase in G0 for the same variation in suction. The fitting parameters of an empirical model for the modulus degradation curve showed that there is a relationship that remains constant along the profile. This relationship was called material constant (κ) and it was found by comparing the results obtained with those available in the literature that the values of κ are higher for finer soils. The improvement of the empirical model used for fitting the degradation curves also included a relationship with the void ratio, which was linear for the soils studied. The integration of the laboratory test data obtained in this research with the in-situ test data available in the literature allowed for a better understanding of the factors that affect the strength and deformability of these soils. In this sense, it was found that there is a good relationship between G0 obtained from bender elements and by the seismic dilatometer test. In addition, it was found that the G0/qmax ratio is higher for the upper soil layer, as well as the G0/qc ratio. It indicates that this part of the soil profile is indeed more developed with presence of cementation. The results obtained in this research enlarge the database of geotechnical parameters for the studied soil profile, contributing to the integration between field and laboratory test results for an unsaturated soil profile of tropical origin.
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Palavras-chave
Solos tropicais, Solos não saturados, Mecânica do solo, Ensaios triaxiais, Resistência ao cisalhamento, Curva de degradação do módulo, Tropical soils, Unsaturated soils, Triaxial tests, Bender elements, Internal instrumentation, Shear strengt, Deformabilit, Maximum shear modulus.