Quantifying the effect of matric suction on the compressive properties of two agricultural soils using an osmotic oedometer

Abstract

The compaction of cultivated soils by agricultural machines considerably affects both the structure and physical properties of soil, thus having a major impact on crop production and the environment. Soil mechanical resistance is highly variable both in time and space because it depends on soil texture, soil porosity and soil water state (matric suction). This paper is devoted to the effect of soil matric suction on the compression index C c , which is one of the mechanical parameters that describes the soil mechanical resistance to compression. We performed oedometer compression tests to study the compression index of a loamy soil and a sandy clay, with matric suction control, by using the osmotic technique. Soil samples were prepared by compacting soil passed through a 2 mm sieve at dry bulk densities of 1.1 and 1.45 Mg m −3 . The mechanical stress and matric suction ranges considered corresponded to field condition, with vertical stress less than 800 kPa and matric suction less than 200 kPa. The results show that the compression index C c was constant or changed little with matric suctions for the two soils at different initial densities. For the loamy soil, the average compression index C c equals 0.73 for an initial bulk density of 1.1 Mg m −3 and 0.41 for 1.45 Mg m −3 for matric suction higher than 20 kPa. For the sandy clay, the average compression index C c is 0.35. From a practical point of view, our study shows that the mathematical determination of mechanical parameters should be standardized due to the S-shaped compression curves that may significantly impact the compression index estimation. The observation of constant compression index with matric suction is a useful result for modelling soil strain due to traffic and predicting the compaction of cultivated soils.

Compressive response of some agricultural soils influenced by the mineralogy and moisture

“…CEC characteristics of the studied soils parameters of the soil is not surprising. Some previous research results have shown that water retention is a complex function of soil structure and composition (Cui et al, 2010;Rawls et al, 2003). We observed in this study that the interaction between moisture retention and the clay content of the sample varied at different matric potential.…”

Triaxial Testing to Determine the Effect of Soil Type and Organic Carbon Content on Soil Consolidation and Shear Deformation Characteristics

“…An alternative to uniaxial testing is triaxial testing, which differs in two respects: (i) both the radial and axial stresses applied to the soil are controlled and (ii) the pore water pressure is usually either controlled or measured. Although, pore water pressure can be controlled in uniaxial tests (e.g., Cui et al, 2010), it is not the norm. Triaxial testing allows the effects of both consolidation and shear deformation on soil density (or porosity) to be quantified.…”

Tensões e deformações em solos devido ao tráfego agrícola: medições e simulações

“…A compactação é puramente a mudança de volume do solo (Horn et al, 2003;Keller et al, 2007), e a densidade, portanto, é uma medida física simples que efetivamente quantifica a compactação por efeito de cargas externas provenientes do tráfego (O'Sullivan et al, 1999). Entretanto, acompanhada da variação de volume, outros efeitos negativos resultados da compactação podem ser observados, tais como alterações na estrutura , sucção matricial (h) Cui et al, 2010), resistência à penetração (RP) (O'Sullivan et al, 1987;Silva et al, 1994;Keller et al, 2013) e dinâmica do fluxo de oxigênio na matriz do solo (Ball et al, 1988;Silva et al, 1994;Berisso et al, 2013).…”

“…Como colocado, mudanças de RP e h pós-tráfego trariam problemas de interpretação quanto aos danos causados para as plantas, mas são úteis como indicares de compactação e resistência do solo O'Sullivan et al, 1987;Cui et al, 2010;Severiano et al, 2013;Keller et al, 2013;Stettler et al, 2014). A RP é frequentemente usada como indicador de compactação (O'Sullivan et al, 1987;Keller et al, 2013), e h é usado nos modelos de resistência do solo (Cui et al, 2010;Severiano et al, 2013;Stettler et al, 2014). Entretanto, como a RP e h não dependem apenas da alteração de volume, alterações imediatamente pós-tráfego podem não ser observadas, mesmo com o incremento de densidade O'Sullivan et al, 1987;Cui et al, 2010).…”

“…A RP é frequentemente usada como indicador de compactação (O'Sullivan et al, 1987;Keller et al, 2013), e h é usado nos modelos de resistência do solo (Cui et al, 2010;Severiano et al, 2013;Stettler et al, 2014). Entretanto, como a RP e h não dependem apenas da alteração de volume, alterações imediatamente pós-tráfego podem não ser observadas, mesmo com o incremento de densidade O'Sullivan et al, 1987;Cui et al, 2010). (Horn et al, 2003;O'Sullivan et al, 1996;O'Sullivan et al, 1999;Keller et al, 2007).…”