scholarly journals Examining the effect of pore size distribution and shape on flow through unsaturated peat using 3-D computed tomography

2009 ◽  
Vol 6 (3) ◽  
pp. 3835-3862 ◽  
Author(s):  
F. Rezanezhad ◽  
W. L. Quinton ◽  
J. S. Price ◽  
D. Elrick ◽  
T. R. Elliot ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Hydraulic Conductivity ◽  
Pore Structure ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Water Pressure ◽  
Pressure Head ◽  
Peat Soils ◽  
Unsaturated Hydraulic Conductivity

Abstract. The hydraulic conductivity of unsaturated peat soils is controlled by the peat structure which affects the air-filled porosity, pore size distribution and shape. This study investigates how the size and shape of pores affects the flow of water through peat soils. In this study we used X-ray Computed Tomography (CT), at 45 µm resolution under 5 specific soil-water pressure head levels to provide 3-D, high-resolution images that were used to detect the inner pore structure of peat samples under a changing water regime. Pore structure and configuration were found to be irregular, which affected the rate of water transmission through peat soils. The 3-D analysis suggested that pore distribution is dominated by a single large pore-space. At low pressure head, this single large air-filled pore imparted a more effective flowpath compared to smaller pores. Smaller pores were disconnected and the flowpath was more tortuous than in the single large air-filled pore, and their contribution to flow was negligible when the single large pore was active. We quantify the pore structure of peat soil that affects the hydraulic conductivity in the unsaturated condition, and demonstrate the validity of our estimation of peat unsaturated hydraulic conductivity by making a comparison with a standard permeameter-based method. Estimates of unsaturated hydraulic conductivities were made for the purpose of testing the sensitivity of pore shape and geometry parameters on the hydraulic properties of peats and how to evaluate the structure of the peat and its affects on parameterization. We also studied the ability to quantify these factors for different soil moisture contents in order to define how the factors controlling the shape coefficient vary with changes in soil water pressure head. The relation between measured and estimated unsaturated hydraulic conductivity at various heads shows that rapid initial drainage, that changes the air-filled pore properties, creates a sharp decline in hydraulic conductivity. This is because the large pores readily lose water, the peat rapidly becomes less conductive and the flow path among pores, more tortuous.

scholarly journals Examining the effect of pore size distribution and shape on flow through unsaturated peat using computed tomography

2009 ◽  
Vol 13 (10) ◽  
pp. 1993-2002 ◽  
Author(s):  
F. Rezanezhad ◽  
W. L. Quinton ◽  
J. S. Price ◽  
D. Elrick ◽  
T. R. Elliot ◽  
...  
Keyword(s):  
Computed Tomography ◽  
Hydraulic Conductivity ◽  
Pore Structure ◽  
Pore Size ◽  
Soil Water ◽  
Water Pressure ◽  
Peat Soil ◽  
Pressure Head ◽  
Peat Soils ◽  
Unsaturated Hydraulic Conductivity

Abstract. The hydraulic conductivity of unsaturated peat soil is controlled by the air-filled porosity, pore size and geometric distribution as well as other physical properties of peat materials. This study investigates how the size and shape of pores affects the flow of water through peat soils. In this study we used X-ray Computed Tomography (CT), at 45 μm resolution under 5 specific soil-water pressure head levels to provide 3-D, high-resolution images that were used to detect the inner pore structure of peat samples under a changing water regime. Pore structure and configuration were found to be irregular, which affected the rate of water transmission through peat soils. The 3-D analysis suggested that pore distribution is dominated by a single large pore-space. At low pressure head, this single large air-filled pore imparted a more effective flowpath compared to smaller pores. Smaller pores were disconnected and the flowpath was more tortuous than in the single large air-filled pore, and their contribution to flow was negligible when the single large pore was active. We quantify the pore structure of peat soil that affects the hydraulic conductivity in the unsaturated condition, and demonstrate the validity of our estimation of peat unsaturated hydraulic conductivity by making a comparison with a standard permeameter-based method. Estimates of unsaturated hydraulic conductivities were made for the purpose of testing the sensitivity of pore shape and geometry parameters on the hydraulic properties of peats and how to evaluate the structure of the peat and its affects on parameterization. We also studied the ability to quantify these factors for different soil moisture contents in order to define how the factors controlling the shape coefficient vary with changes in soil water pressure head. The relation between measured and estimated unsaturated hydraulic conductivity at various heads shows that rapid initial drainage, that changes the air-filled pore properties, creates a sharp decline in hydraulic conductivity. This is because the large pores readily lose water, the peat rapidly becomes less conductive and the flow path among pores, more tortuous.

Unsaturated hydraulic conductivity of vineyard soils with high rock fragment content in the Mosel area, Germany

2021 ◽  
Author(s):  
Selina Walle ◽  
Thomas Iserloh ◽  
Manuel Seeger
Keyword(s):  
Hydraulic Conductivity ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Unsaturated Soils ◽  
Hydrological Cycle ◽  
Calculated Data ◽  
Rock Fragment ◽  
Unsaturated Hydraulic Conductivity ◽  
Significant Difference

<p>The study deals with the unsaturated hydraulic conductivity of soils within the scope of the Diverfarming-Project, funded by the EU commission (Horizon 2020 grant agreement no 728003). For this reason, the field work took place in the examined vineyard of the Wawerner Jesuitenberg near Kanzem in the Saar-Mosel valley (Rhineland-Palatinate, Germany). The mentioned parameter is one of the most important specific factors of the hydrological cycle to characterize soil hydraulic properties in the unsaturated soil zone. A mini disc infiltrometer was used to measure the conductivity values at different suctions. The purpose of this study is to determine the plausibility of the fundamentals and the analytical expression of the unsaturated conductivity models in a nearly skeletal soil of schist. In this regard, the mathematical expressions of Mualem (1976), van Genuchten (1980) and Zhang (1997) are focused on calculating the unsaturated hydraulic conductivity. The two variables α and n are analysed in order to better compare between literature specifications and the explicit calculated data of the vineyard’s soil. As a result, the various developments of α are similar thus the significant difference is based on the value of n. Nevertheless, in consideration of these frame conditions the models represent a suitable mathematical expression of the unsaturated hydraulic conductivity. Furthermore, a range of parameters affecting this conductivity is analysed, particularly with regard to the applied variable soil and cultivation management under the grapevines in the vineyard. Also, the rock fragment cover and the pore size distribution are taken into account. In this context the soil compaction and modified pore size distribution in the wheel tracks stand out due to salient unsaturated hydraulic conductivities at higher tensions. In particular, the stone cover of the contact surface influence the characteristics of the analysed conductivity. Additionally, the connection of stone cover, management and pore size distribution creates a mixture of affected parameters of the unsaturated hydraulic conductivity.</p><p> </p><p>Mualem, Y.: A new model for predicting the hydraulic conductivity of unsaturated porous media, Water Resour. Res, 12, 513–522, https://doi.org/10.1029/WR012i003p00513, 1976.</p><p>Van Genuchten, M.T.: A Closed-form Equation for Predicting the Hydraulic Conductivity of Unsaturated Soils, Soil Sci. Soc. Am. J., 44, 892–898, https://doi.org/10.2136/sssaj1980.03615995004400050002x, 1980.</p><p>Zhang, R.: Determination of Soil Sorptivity and Hydraulic Conductivity from the Disk Infiltrometer, Soil Sci. Soc. Am. J., 61, 1024–1030, https://doi.org/10.2136/sssaj1997.03615995006100040005x, 1997.</p>

scholarly journals A Fractal Model of Hydraulic Conductivity for Saturated Frozen Soil

Water ◽  
2019 ◽  
Vol 11 (2) ◽  
pp. 369 ◽  
Author(s):  
Lei Chen ◽  
Dongqing Li ◽  
Feng Ming ◽  
Xiangyang Shi ◽  
Xin Chen
Keyword(s):  
Hydraulic Conductivity ◽  
Pore Structure ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Fractal Theory ◽  
Frozen Soil ◽  
Soil Freezing ◽  
Size Dimension ◽  
Maximum Pore Size

In cold regions, hydraulic conductivity is a critical parameter for determining the water flow in frozen soil. Previous studies have shown that hydraulic conductivity hinges on the pore structure, which is often depicted as the pore size and porosity. However, these two parameters do not sufficiently represent the pore structure. To enhance the characterization ability of the pore structure, this study introduced fractal theory to investigate the influence of pore structure on hydraulic conductivity. In this study, the pores were conceptualized as a bundle of tortuous capillaries with different radii and the cumulative pore size distribution of the capillaries was considered to satisfy the fractal law. Using the Hagen-Poiseuille equation, a fractal capillary bundle model of hydraulic conductivity for saturated frozen soil was developed. The model validity was evaluated using experimental data and by comparison with previous models. The results showed that the model performed well for frozen soil. The model showed that hydraulic conductivity was related to the maximum pore size, pore size dimension, porosity and tortuosity. Of all these parameters, pore size played a key role in affecting hydraulic conductivity. The pore size dimension was found to decrease linearly with temperature, the maximum pore size decreased with temperature and the tortuosity increased with temperature. The model could be used to predict the hydraulic conductivity of frozen soil, revealing the mechanism of change in hydraulic conductivity with temperature. In addition, the pore size distribution was approximately estimated using the soil freezing curve, making this method could be an alternative to the mercury intrusion test, which has difficult maneuverability and high costs. Darcy’s law is valid in saturated frozen silt, clayed silt and clay, but may not be valid in saturated frozen sand and unsaturated frozen soil.

scholarly journals Construction of pore structure and lithology of digital rock physics based on laboratory experiments

2021 ◽  
Vol 11 (5) ◽  
pp. 2113-2125
Author(s):  
Chenzhi Huang ◽  
Xingde Zhang ◽  
Shuang Liu ◽  
Nianyin Li ◽  
Jia Kang ◽  
...  
Keyword(s):  
Pore Structure ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Laboratory Experiments ◽  
Rock Physics ◽  
Reconstruction Method ◽  
Digital Rock Physics ◽  
Digital Rock ◽  
The Core

AbstractThe development and stimulation of oil and gas fields are inseparable from the experimental analysis of reservoir rocks. Large number of experiments, poor reservoir properties and thin reservoir thickness will lead to insufficient number of cores, which restricts the experimental evaluation effect of cores. Digital rock physics (DRP) can solve these problems well. This paper presents a rapid, simple, and practical method to establish the pore structure and lithology of DRP based on laboratory experiments. First, a core is scanned by computed tomography (CT) scanning technology, and filtering back-projection reconstruction method is used to test the core visualization. Subsequently, three-dimensional median filtering technology is used to eliminate noise signals after scanning, and the maximum interclass variance method is used to segment the rock skeleton and pore. Based on X-ray diffraction technology, the distribution of minerals in the rock core is studied by combining the processed CT scan data. The core pore size distribution is analyzed by the mercury intrusion method, and the core pore size distribution with spatial correlation is constructed by the kriging interpolation method. Based on the analysis of the core particle-size distribution by the screening method, the shape of the rock particle is assumed to be a more practical irregular polyhedron; considering this shape and the mineral distribution, the DRP pore structure and lithology are finally established. The DRP porosity calculated by MATLAB software is 32.4%, and the core porosity measured in a nuclear magnetic resonance experiment is 29.9%; thus, the accuracy of the model is validated. Further, the method of simulating the process of physical and chemical changes by using the digital core is proposed for further study.

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