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Rainer Horn - One of the best experts on this subject based on the ideXlab platform.
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effect of hydraulic and mechanical stresses on cyclic deformation processes of a structured and homogenized silty luvic chernozem
Soil & Tillage Research, 2012Co-Authors: Anneka Mordhorst, Iris Zimmermann, Stephan Peth, Rainer HornAbstract:The deformation behavior of Soils is strongly affected by coupled mechanical and hydraulic stresses especially under cyclic Loading. Contrary to static Loading tests cyclic Loading caused plastic deformation increments with ongoing Loading cycles even for stresses in the re-compression range associated with alterations in the hydraulic stress state. The aim of this study was to proof the interference of hydraulic properties on the mechanical deformation behavior (cyclic compressibility) depending on Soil structure and cyclic Loading time. Cyclic Loading tests with changing boundary conditions in terms of initial matric potential, Loading time and magnitude on structured and homogenized silty Soil samples were performed. Furthermore, pore water pressures during cyclic Loading and the air conductivity of Soil cores before and after cyclic Loading were measured. The results indicated differences in the stress strain response accompanied by typical hydraulic stress regimes. These were classified into five categories representing a typical development of pore water pressures according to Soil structure and Loading time. Predominantly at short-time cycles a built-up of pore water pressures with increasing number of cycles occurred resulting in a high cyclic compressibility of the homogenized Soil. The loss of Soil strength could be linked to the beginning of partial liquefaction processes induced by heavy Soil Loading of 150 kPa and by a higher initial matric potential. In contrast, the less compressible structured Soil showed a better internal redistribution of pore water and faster dissipation of stress-induced pore water pressures compared to the homogenized Soil. Finally, the influence of Soil structure plays an important role in understanding hydro-mechanical relationships, especially since the reversal of pore water pressures back to the hydraulic equilibrium state was restricted by the time between repeated Loading events. (C) 2012 Elsevier B.V. All rights reserved.
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Soil compaction processes and their effects on the structure of arable Soils and the environment
Soil & Tillage Research, 1995Co-Authors: Rainer Horn, H Domzzal, Anna Slowinskajurkiewicz, C Van OuwerkerkAbstract:Soils are three-phase systems which undergo changes as soon as the external stresses exceed the internal Soil strength, defined by the precompression stress value. The three-dimensional stress propagation induces corresponding volumetric Soil strain. Soil compaction can result either in a higher bulk density or, when Soil Loading is attended with retarded water fluxes and high dynamic forces, in a completely homogenised Soil characterised by a lower bulk density and a predominance of fine pores. While in natural Soils the structure can be described as macroscopically homogeneous, less careful mechanical treatment or reduced addition of organic substances results in less favourable types of Soil aggregates. As a result of applied external stresses, physical and chemical processes, such as mass flow and diffusion of water, ions and gases, are at least retarded or even completely altered. Both increased bulk density and homogenisation cause decreased aeration and increased penetration resistance, which results in impeded root development. Reduced water permeability may result in Soil erosion, with serious negative effects on the environment. Compacted Soil may also contribute to global atmospheric warming due to increased emission of CO2, CH4 and N2O from such Soils. Anthropogenic changes in Soil structure and Soil functions remain constant for extended periods of time and efforts to restore deteriorated Soil structure very often fail because of excessive loosening and homogenisation, cultivation of too wet Soil or, afterwards, ill-adapted Soil management practices, resulting in even worse Soil properties. The present paper gives a summary of relevant work performed by the authors.
C Van Ouwerkerk - One of the best experts on this subject based on the ideXlab platform.
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Soil compaction processes and their effects on the structure of arable Soils and the environment
Soil & Tillage Research, 1995Co-Authors: Rainer Horn, H Domzzal, Anna Slowinskajurkiewicz, C Van OuwerkerkAbstract:Soils are three-phase systems which undergo changes as soon as the external stresses exceed the internal Soil strength, defined by the precompression stress value. The three-dimensional stress propagation induces corresponding volumetric Soil strain. Soil compaction can result either in a higher bulk density or, when Soil Loading is attended with retarded water fluxes and high dynamic forces, in a completely homogenised Soil characterised by a lower bulk density and a predominance of fine pores. While in natural Soils the structure can be described as macroscopically homogeneous, less careful mechanical treatment or reduced addition of organic substances results in less favourable types of Soil aggregates. As a result of applied external stresses, physical and chemical processes, such as mass flow and diffusion of water, ions and gases, are at least retarded or even completely altered. Both increased bulk density and homogenisation cause decreased aeration and increased penetration resistance, which results in impeded root development. Reduced water permeability may result in Soil erosion, with serious negative effects on the environment. Compacted Soil may also contribute to global atmospheric warming due to increased emission of CO2, CH4 and N2O from such Soils. Anthropogenic changes in Soil structure and Soil functions remain constant for extended periods of time and efforts to restore deteriorated Soil structure very often fail because of excessive loosening and homogenisation, cultivation of too wet Soil or, afterwards, ill-adapted Soil management practices, resulting in even worse Soil properties. The present paper gives a summary of relevant work performed by the authors.
Anneka Mordhorst - One of the best experts on this subject based on the ideXlab platform.
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effect of hydraulic and mechanical stresses on cyclic deformation processes of a structured and homogenized silty luvic chernozem
Soil & Tillage Research, 2012Co-Authors: Anneka Mordhorst, Iris Zimmermann, Stephan Peth, Rainer HornAbstract:The deformation behavior of Soils is strongly affected by coupled mechanical and hydraulic stresses especially under cyclic Loading. Contrary to static Loading tests cyclic Loading caused plastic deformation increments with ongoing Loading cycles even for stresses in the re-compression range associated with alterations in the hydraulic stress state. The aim of this study was to proof the interference of hydraulic properties on the mechanical deformation behavior (cyclic compressibility) depending on Soil structure and cyclic Loading time. Cyclic Loading tests with changing boundary conditions in terms of initial matric potential, Loading time and magnitude on structured and homogenized silty Soil samples were performed. Furthermore, pore water pressures during cyclic Loading and the air conductivity of Soil cores before and after cyclic Loading were measured. The results indicated differences in the stress strain response accompanied by typical hydraulic stress regimes. These were classified into five categories representing a typical development of pore water pressures according to Soil structure and Loading time. Predominantly at short-time cycles a built-up of pore water pressures with increasing number of cycles occurred resulting in a high cyclic compressibility of the homogenized Soil. The loss of Soil strength could be linked to the beginning of partial liquefaction processes induced by heavy Soil Loading of 150 kPa and by a higher initial matric potential. In contrast, the less compressible structured Soil showed a better internal redistribution of pore water and faster dissipation of stress-induced pore water pressures compared to the homogenized Soil. Finally, the influence of Soil structure plays an important role in understanding hydro-mechanical relationships, especially since the reversal of pore water pressures back to the hydraulic equilibrium state was restricted by the time between repeated Loading events. (C) 2012 Elsevier B.V. All rights reserved.
Josep M Bayona - One of the best experts on this subject based on the ideXlab platform.
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screening of 47 organic microcontaminants in agricultural irrigation waters and their Soil Loading
Water Research, 2011Co-Authors: Diana Calderonpreciado, C Jimenezcartagena, Victor Matamoros, Josep M BayonaAbstract:Abstract Reclaimed water usage for crop irrigation is viewed both as an excellent sustainable water source and as a potential entrance for emerging organics into the food chain. This concern is backed by the already documented pollutant crop uptake potential. In the present study, irrigation waters used in agricultural fields (Torroella de Montgri, NE Spain) were screened for 47 analytes in a two year study (2007–2008). A total of 26 contaminants belonging to different chemical classes namely, pesticides, pharmaceuticals, personal care products, phenolic estrogens, antioxidants and disinfection by-products, were detected. Marked differences in concentration trends for the different chemical classes were evidenced from 2007 to 2008, and attributed to a persistent drought endured by the region in 2008. Also, Loading mass rates of chemical classes were estimated based on crop irrigation regimes and they ranged from 0.8 to 121.3 g ha −1 per crop cycle. These values were contrasted with those obtained for other water sources from countries where crop irrigation is commonly practiced. Finally, crops grown under these irrigation regimes, namely alfalfa and apple, were analyzed and 5 anthropogenic compounds were identified and quantitated, whose concentrations ranged from 13.9 to 532 ng g −1 (fresh weight).
C Jimenezcartagena - One of the best experts on this subject based on the ideXlab platform.
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screening of 47 organic microcontaminants in agricultural irrigation waters and their Soil Loading
Water Research, 2011Co-Authors: Diana Calderonpreciado, C Jimenezcartagena, Victor Matamoros, Josep M BayonaAbstract:Abstract Reclaimed water usage for crop irrigation is viewed both as an excellent sustainable water source and as a potential entrance for emerging organics into the food chain. This concern is backed by the already documented pollutant crop uptake potential. In the present study, irrigation waters used in agricultural fields (Torroella de Montgri, NE Spain) were screened for 47 analytes in a two year study (2007–2008). A total of 26 contaminants belonging to different chemical classes namely, pesticides, pharmaceuticals, personal care products, phenolic estrogens, antioxidants and disinfection by-products, were detected. Marked differences in concentration trends for the different chemical classes were evidenced from 2007 to 2008, and attributed to a persistent drought endured by the region in 2008. Also, Loading mass rates of chemical classes were estimated based on crop irrigation regimes and they ranged from 0.8 to 121.3 g ha −1 per crop cycle. These values were contrasted with those obtained for other water sources from countries where crop irrigation is commonly practiced. Finally, crops grown under these irrigation regimes, namely alfalfa and apple, were analyzed and 5 anthropogenic compounds were identified and quantitated, whose concentrations ranged from 13.9 to 532 ng g −1 (fresh weight).