Microstructural strength of four subtropical soils evaluated by rheometry: properties, difficulties and opportunities

The structural strength of soils has been extensively described by physical and mechanical properties evaluated on the mesoscale for different soils and management conditions. However, changes in the organization of the soil matrix at the microstructural level, which can be obtained by rheometry, are still seldom used in soil mechanics. Our aim was to use the amplitude sweep test, a rheometry technique, to investigate the microstructural strength of four subtropical soils (two Oxisols, an Ultisol and a Vertisol) and to discuss difficulties with respect to the samples, water content, soil density and vertical force. The various rheological properties which reveal the soil microstructural strength were determined: deformation at the end of the linear viscoelastic range, LVE range (LVE), shear stress at the end of the LVE range (LVE), deformation at yield point, YP (YP), storage and loss moduli at YP (GGYP), maximum shear stress (max), and integral z. In general, soil elasticity (LVE and YP) and microstructural strength (LVE and max) were greater in the Oxisols and the Vertisol, which both possess high clay content, while the latter also contains expansive clay minerals. The lowest structural strength was observed in the Ultisol which had a high sand content. As rheological properties are related to soil properties such as particle size distribution and carbon content, they can be applied in the evaluation of the microstructural strength of clayey and sandy soils and allows for inferences regarding inter-particle shear strength. However, the test is not applicable to very dry soil samples and sample preparations can affect the results. We suggest a number of approaches to find solutions for these difficulties/problems.

Microstructural strength of four subtropical soils evaluated by rheometry: properties, difficulties and opportunities

The structural strength of soils has been extensively described by physical and mechanical properties evaluated on the mesoscale for different soils and management conditions. However, changes in the organization of the soil matrix at the microstructural level, which can be obtained by rheometry, are still seldom used in soil mechanics. Our aim was to use the amplitude sweep test, a rheometry technique, to investigate the microstructural strength of four subtropical soils (two Oxisols, an Ultisol and a Vertisol) and to discuss difficulties with respect to the samples, water content, soil density and vertical force. The various rheological properties which reveal the soil microstructural strength were determined: deformation at the end of the linear viscoelastic range, LVE range (LVE), shear stress at the end of the LVE range (LVE), deformation at yield point, YP (YP), storage and loss moduli at YP (GGYP), maximum shear stress (max), and integral z. In general, soil elasticity (LVE and YP) and microstructural strength (LVE and max) were greater in the Oxisols and the Vertisol, which both possess high clay content, while the latter also contains expansive clay minerals. The lowest structural strength was observed in the Ultisol which had a high sand content. As rheological properties are related to soil properties such as particle size distribution and carbon content, they can be applied in the evaluation of the microstructural strength of clayey and sandy soils and allows for inferences regarding inter-particle shear strength. However, the test is not applicable to very dry soil samples and sample preparations can affect the results. We suggest a number of approaches to find solutions for these difficulties/problems.(AU)

Mechanical properties of baru fruit (Dipteryx alata Vogel) / Propriedades mecânicas dos frutos de baru (Dipteryx alata Vogel)

This paper aimed to verify the influence of moisture content and drying temperature on the values of maximum compression strength for fixed strains (1; 2; 3; 4; 5; 6; and 7 mm), rupture force, and proportional deformity modulus on the baru fruit (Dipteryx alata Vogel) under compression in a natural resting position. Baru fruits with a moisture content ranging from 0.333 to 0.053 (decimal dry basis db) were used. The fruits were uniaxially compressed between two parallel plates, in the natural resting position, and the nuts were dried at temperatures of 60, 80, and 100 °C. The reduction in the moisture content during drying was monitored using a gravimetric method (weight loss) to determine the initial moisture content of the product and the final moisture content. Based on our results, the compression force needed to deform the baru fruit decreased with increasing moisture content, regardless of the drying temperature. The proportional deformity modulus increased with the reduction of moisture content for all the studied temperatures. The reduced moisture content increased the force required to rupture the baru fruit, regardless of the drying temperature. The rupture forces of temperatures of 60 to 100 °C may be represented by one model.(AU)

Neste trabalho objetivou-se verificar a influência do teor de água e da temperatura de secagem nos valores da força máxima de compressão para deformações fixas (1, 2, 3, 4, 5, 6 e 7 mm), força de ruptura e no módulo proporcional de deformidade nos frutos de baru (Dipteryx alata Vogel), submetidos à compressão na posição natural de repouso. Foram utilizados frutos de baru com teores de água variando de 0,333 a 0,053 (decimal b.s.), secos nas temperaturas de 60, 80 e 100 °C. A redução do teor de água ao longo da secagem foi acompanhada pelo método gravimétrico (perda de massa), conhecendo-se o teor de água inicial do produto, até atingir o teor de água final. Concluiu-se que a força de compressão necessária para deformar os frutos de baru diminui com o aumento do teor de água, independentemente da temperatura de secagem. O módulo proporcional de deformidade aumenta com a redução do teor de água para todas as temperaturas estudadas. A redução do teor de água eleva a força necessária à ruptura dos frutos de baru, independentemente da temperatura de secagem. As forças de ruptura para as temperaturas de 60 e 100 °C podem ser representadas por um único modelo.(AU)

Ensaio de Proctor normal – análise metodológica e planilha para cálculo da densidade do solo máxima e teor de água ótimo / Proctor compaction test – methodology analysis and worksheet to calculate the maximum soildensity and optimum moisture content

A definição de limites críticos de densidade do solo para o desenvolvimento das plantas é muito complexa, uma vez que é dependente da textura e do teor de matéria orgânica. A densidade relativa, que é a relação entre a densidade do solo no campo e a densidade do solo máxima obtida pelo ensaio de Proctor normal, tem sido apresentada como um parâmetro capaz de padronizar e delimitar esses limites críticos. O objetivo deste trabalho é descrever os procedimentos que devem ser adotados para a realização de um ensaio de Proctor normal e disponibilizar uma planilha eletrônica Excel. A planilha auxilia no cálculo do teor de água que as amostras a serem compactadas devem atingir, além de calcular a densidade do solo máxima e o teor de água do solo ótimo para compactação a partir de equação de 2° grau obtida de forma analítica a partir de um conjunto de dados não balanceados.

The definition of critical limits of soil density for development of plants is very complex, since it is dependent on the texture and organic matter content. The relative compaction, that is the percentage ratio of the bulk density to the maximum dry density as determined by the Proctor compaction test, has been presented as a parameter capable of standardizing and delimiting these critical limits. The aim of this study is to describe the procedures that have to be used for the implementation of a Proctor compaction test and make available an Excel worksheet that assists in the calculation of water content that the samples to be compacted must reach, besides calculating maximum dry density and optimum moisture content of soil from equation of degree 2 obtained by analytical form from an unbalanced data set.

Ensaio de Proctor normal análise metodológica e planilha para cálculo da densidade do solo máxima e teor de água ótimo / Proctor compaction test methodology analysis and worksheet to calculate the maximum soildensity and optimum moisture content

A definição de limites críticos de densidade do solo para o desenvolvimento das plantas é muito complexa, uma vez que é dependente da textura e do teor de matéria orgânica. A densidade relativa, que é a relação entre a densidade do solo no campo e a densidade do solo máxima obtida pelo ensaio de Proctor normal, tem sido apresentada como um parâmetro capaz de padronizar e delimitar esses limites críticos. O objetivo deste trabalho é descrever os procedimentos que devem ser adotados para a realização de um ensaio de Proctor normal e disponibilizar uma planilha eletrônica Excel. A planilha auxilia no cálculo do teor de água que as amostras a serem compactadas devem atingir, além de calcular a densidade do solo máxima e o teor de água do solo ótimo para compactação a partir de equação de 2° grau obtida de forma analítica a partir de um conjunto de dados não balanceados.(AU)

The definition of critical limits of soil density for development of plants is very complex, since it is dependent on the texture and organic matter content. The relative compaction, that is the percentage ratio of the bulk density to the maximum dry density as determined by the Proctor compaction test, has been presented as a parameter capable of standardizing and delimiting these critical limits. The aim of this study is to describe the procedures that have to be used for the implementation of a Proctor compaction test and make available an Excel worksheet that assists in the calculation of water content that the samples to be compacted must reach, besides calculating maximum dry density and optimum moisture content of soil from equation of degree 2 obtained by analytical form from an unbalanced data set.(AU)

Mechanical properties of baru fruit (Dipteryx alata Vogel) / Propriedades mecânicas dos frutos de baru (Dipteryx alata Vogel)

This paper aimed to verify the influence of moisture content and drying temperature on the values of maximum compression strength for fixed strains (1; 2; 3; 4; 5; 6; and 7 mm), rupture force, and proportional deformity modulus on the baru fruit (Dipteryx alata Vogel) under compression in a natural resting position. Baru fruits with a moisture content ranging from 0.333 to 0.053 (decimal dry basis – db) were used. The fruits were uniaxially compressed between two parallel plates, in the natural resting position, and the nuts were dried at temperatures of 60, 80, and 100 °C. The reduction in the moisture content during drying was monitored using a gravimetric method (weight loss) to determine the initial moisture content of the product and the final moisture content. Based on our results, the compression force needed to deform the baru fruit decreased with increasing moisture content, regardless of the drying temperature. The proportional deformity modulus increased with the reduction of moisture content for all the studied temperatures. The reduced moisture content increased the force required to rupture the baru fruit, regardless of the drying temperature. The rupture forces of temperatures of 60 to 100 °C may be represented by one model.

Neste trabalho objetivou-se verificar a influência do teor de água e da temperatura de secagem nos valores da força máxima de compressão para deformações fixas (1, 2, 3, 4, 5, 6 e 7 mm), força de ruptura e no módulo proporcional de deformidade nos frutos de baru (Dipteryx alata Vogel), submetidos à compressão na posição natural de repouso. Foram utilizados frutos de baru com teores de água variando de 0,333 a 0,053 (decimal b.s.), secos nas temperaturas de 60, 80 e 100 °C. A redução do teor de água ao longo da secagem foi acompanhada pelo método gravimétrico (perda de massa), conhecendo-se o teor de água inicial do produto, até atingir o teor de água final. Concluiu-se que a força de compressão necessária para deformar os frutos de baru diminui com o aumento do teor de água, independentemente da temperatura de secagem. O módulo proporcional de deformidade aumenta com a redução do teor de água para todas as temperaturas estudadas. A redução do teor de água eleva a força necessária à ruptura dos frutos de baru, independentemente da temperatura de secagem. As forças de ruptura para as temperaturas de 60 e 100 °C podem ser representadas por um único modelo.