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... potential: Piezometers are commonly applied to measure ψ p . A piezometer (Fig.2) is a tube that is placed in the soil to depths below the water table and that extends to the soil surface and is open to the atmosphere. The bottom of the piezometer is perforated to allow soil water under positive hydrostatic pressure to enter the tube. ...
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Core Ideas
Matric potential controls the equilibrium fractionation factor between soil water and water vapor.
Surface chemistry determined by X‐ray spectroscopy affects the equilibrium fractionation factor.
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Citations
... As the result of an energy deficit between soil water and pure water, total soil water potential is designated as negative by convention. The total potential of soil water mainly consists of three forms of energy: gravitational, osmotic, and matric potentials (e.g., Hillel 1998;Lu and Likos 2004;Or et al. 2005;Osman 2013). Among these three potentials, matric potential is often dominant; thus, it can be practically considered as the total potential in most geotechnical engineering problems. ...
Total soil water potential ψt is conventionally defined as the sum of matric potential ψm and osmotic potential ψo, i.e., ψt=ψm+ψo, when gravitational potential is ignored. Soil water isotherm (SWI) is the constitutive relationship between ψt and soil water content w, i.e., ψt(w)=ψm(w)+ψo, where ψm(w) is called soil water retention curve (SWRC) or soil water characteristic curve. SWI and SWRC are arguably the two most important soil constitutive relationships because they govern virtually all phenomena in soil such as flow, stress and deformation, and biological activities. A closed-form SWI, recast from a generalized SWRC equation for adsorption and capillarity, is experimentally validated for its generality in representing SWI. Adsorption isotherms of 49 soils, covering all spectrum of soil types with plasticity index up to 185% and specific surface area up to 600 m2/g, are used to validate the SWI equation. It is shown that the SWI equation can nearly perfectly represent the isotherms of these soils with almost all of the coefficients of determination R2≥0.99, validating the generality of the SWI equation. Comparative analysis is also conducted by using two existing SWI equations, namely, the Brunauer-Emmett-Teller (BET) equation and the augmented BET (A-BET) equation. It is demonstrated that the SWI equation is superior to the BET and A-BET equations in representing soil-water interactions by adsorption and capillarity, and in the full relative humidity range.
... The Soil Water Potential is defined as [15]: "The amount of work that an infinitesimal unit quantity of water at equilibrium is capable of doing when it moves (isothermally and reversibly) to a pool of water at similar standard (reference) state, i.e., similar pressure, elevation, temperature and chemical composition ". Dani Or, Markus Tuller and Jon M. Wraith [15] proposed experimental or numerical calculation method of soil water potential. ...
... The Soil Water Potential is defined as [15]: "The amount of work that an infinitesimal unit quantity of water at equilibrium is capable of doing when it moves (isothermally and reversibly) to a pool of water at similar standard (reference) state, i.e., similar pressure, elevation, temperature and chemical composition ". Dani Or, Markus Tuller and Jon M. Wraith [15] proposed experimental or numerical calculation method of soil water potential. ...
The arctic region hold abundant oil & gas resources according to the assessment by United States Geological Survey (USGS) in 2009. While, the thaw of permafrost during drilling operation can lead to the instability of wellhead. A coupled thermal model between wellbore and formation is given considering the latent heat of fusing and migration of water during the thaw of permafrost, and the thawed permafrost zone can be estimated. A wellhead stability analysis method considering heat transferred from wellbore is also proposed in this paper. FLAC3D software is applied to analyze the wellhead stability. Some conclusions are made through a case study: Flow in the wellbore delivers heat from deep part of formation to the shallow part of the formation, which leads to the permafrost thaws. Thawed permafrost losses most of the shear strength compared to that of the frozen permafrost which leads to the settlement of wellhead. The calculated results using FLAC3D software shows that the wellhead settles as deep as 0.66 m resulting from the permafrost thaw. In addition, the installation of anti-sinking pad is suggested to reduce the wellhead settlement. According to our simulation, the anti-sinking pad with radius of 8 times the wellhead radius is suggested, which can reduce the wellhead settlement to 0.1 m.
... Sub-samples of the homogenized soils were dried at 40 C for physical and chemical analyses. Soil water holding capacity was measured by the volumetric method using char free soils (Livingston and Topp, 2007). Soil carbon and nitrogen concentrations were measured from ballmilled sub-samples by elemental analysis ( " Vario Max " , Elementar Analysensysteme GmbH, Hanau) before and after incubation . ...
In the mid‐20th century, harnessing of thermodynamics in describing water movement in soil, viz the concept of water potential, marks the emergence of modern soil physics, unsaturated soil mechanics, and vadose zone hydrology. Yet to date, a seamless linkage between thermodynamics and water potential is still missing, leading to several long‐lasting dilemmas regarding soil properties, for example, abnormal soil water density, peculiar film water viscosity and relative permittivity, pore water pressure, and water freezing temperature depression. Here, a thermodynamic framework is established by synthesizing recent advancements in soil‐water interaction. The classical thermodynamic concepts are revisited, highlighting the difference between macroscopic systems commonly treated in conventional theories and the intermolecular scale system subject to external fields. Soil water is conceived as an intermolecular scale open thermodynamic system subject to external fields of gravity, osmosis, and adsorption. The formulated thermodynamic framework is verified by reducing to the conventional definition of matric potential and a recently proposed unitary definition. The accuracy of the framework is further justified in terms of mechanical equilibrium criteria. The framework predicts the existence of spatially varied pore water pressure in soil pores and can serve as the theoretical basis for reconciling the physical origin of abnormal soil behavior such as water density, film water viscosity, relative permittivity, and negative or positive pore water pressure.
Soil aeration affects plant growth, nutrient cycling, greenhouse gas emissions, soil remediation, and soil morphology. In a general sense, soil aeration is the interchange of gases between the atmosphere and the earth, but often refers more specifically to oxygen status which is largely affected by respiration of plant roots and soil microbes. Soil-atmosphere exchange of gases also results from other biogeochemical reactions that consume or produce gases and physical processes of diffusion and convection which are influenced by soil texture, structure, water content, and temperature. This chapter provides an overview of the key processes affecting and affected by soil aeration.
Résumé: Ce mémoire s'inscrit dans le cadre du projet de recherche BAG'AGES (2016-2020) ayant pour objectif d'évaluer les performances des pratiques agroécologiques (diminution du travail du sol, couverts végétaux, diversification de la rotation) du bassin Adour-Garonne sur la dynamique de l'eau, afin de promouvoir une agriculture durable. L'objectif de ce travail consiste à apporter des éléments de compréhension sur les effets engendrés par les pratiques agroécologiques, employées sur quatre sites du bassin (Tarn 1, Tarn 2, Gers, Pyrénées-Atlantiques), sur l'infiltration et la rétention de l'eau dans les sols. Pour répondre à cet objectif, la quantité de matières organiques, la densité apparente, la conductivité hydraulique K(h) et la teneur en eau θ (h) ont été comparé, sur chaque site, entre un système conventionnel et un système mobilisant des pratiques agroécologiques. L'ensemble des mesures ont été effectuées post récolte (octobre-décembre 2016) sur l'horizon de surface (0-5 cm). Les résultats de cette étude ont montré que, en favorisant la porosité du sol (structure, connectivité, distribution de la taille des pores), l'agriculture de conservation améliore l'infiltration et la rétention de l'eau dans les sols. Ces résultats sont cependant différents lorsque la comparaison est effectuée avec un sol récemment travaillé. Le passage de l'outil dans le sol provoque une élévation de la quantité de macropores, ce qui favorise, à court terme la rétention de l'eau à saturation et l'infiltration.
Hysteresis is a widely reported phenomenon in natural and engineered systems across different temporal and spatial scales. Its definition is non-unique and rather context-dependent, while systems with hysteretic behavior, including hydrological systems, are commonly referred to as path-dependent systems or systems with memory. Despite widespread existence of hysteretic processes, the current generation of hydrologic models do not directly account for hysteresis. In this paper, we review the fundamentals, theories, and general properties of hysteresis in the broad scientific literature and then focus on its representations in hydrological sciences. Through illustrative examples, we show how an incomplete understanding or representation of the underlying processes in a system can lead to considering the system as being path-dependent. We argue that, in most cases, hysteresis is a manifestation of our dimensionality-reducing approach to process understanding and representation. We further explain that modelling hysteresis in an ideal world requires a full-dimensional process representation, based on a perfect understanding of the processes, their heterogeneity, and their spatio-temporal scale dependency. We discuss, however, that the missing dimensions/physics in a hydrologic model may be compensated to some extent by enabling the model with formal hysteretic components. Moreover, we show that the conventional model structure and parameterization may be designed in a way to partially reproduce a desired hysteretic behavior.
