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 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 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.

scholarly journals Experimental investigation on pore size distribution and drying kinetics during lyophilization of sugar solutions

2018 ◽  
Author(s):  
Petra Foerst ◽  
M. Lechner ◽  
N. Vorhauer ◽  
H. Schuchmann ◽  
E. Tsotsas
Keyword(s):  
Pore Structure ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Freeze Drying ◽  
Three Dimensional ◽  
Drying Kinetics ◽  
Process Efficiency ◽  
Freeze Dried ◽  
Pore Size Distributions

The pore structure is a decisive factor for the process efficiency and product quality of freeze dried products. In this work the two-dimensional ice crystal structure was investigated for maltodextrin solutions with different concentrations by a freeze drying microscope. The resulting drying kinetics was investigated for different pore structures. Additionally the three-dimensional pore structure of the freeze dried samples was measured by µ-computed tomography and the pore size distribution was quantified by image analysis techniques. The two- and three-dimensional pore size distributions were compared and linked to the drying kinetics.Keywords: pore size distribution; freeze drying; maltodextrin solution; freeze drying microscope   

scholarly journals Investigation on the Deterioration Mechanism of Tuff Stones Used for the Exteriors at the Former Koshien Hotel

2020 ◽  
Vol 172 ◽  
pp. 20008
Author(s):  
Koki Yamada ◽  
Chiemi Iba ◽  
Tomoko Uno ◽  
Kazuma Fukui ◽  
Daisuke Ogura
Keyword(s):  
Hydraulic Conductivity ◽  
Physical Properties ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Vapor Permeability ◽  
Cultural Significance ◽  
Water Permeation ◽  
Deterioration Mechanism ◽  
Main Factor

The former Koshien Hotel is an historic Japanese architectural structure, where two different tuffs called Nikkaseki and Tatsuyamaishi were used to build the exterior. Despite its cultural significance, the building’s exterior is deteriorating in many ways, with water permeation being the main factor. In this study, the hygrothermal properties of both Nikkaseki and Tatsuyamaishi were measured in order to examine the correlation between deterioration mechanisms and the tuff characteristics in detail. The basic physical properties, pore size distribution, vapor permeability, hydraulic conductivity, and sorption isotherm were measured. The results of a comparison of two tuffs led us to hypothesize that the main reason behind Nikkaseki’s deterioration is expansive freezing, while that of Tatsuyamaishi is caused by repeating dehydration or dry-wet cycles.

scholarly journals Ink-bottle Effect and Pore Size Distribution of Cementitious Materials Identified by Pressurization–Depressurization Cycling Mercury Intrusion Porosimetry

Materials ◽  
2019 ◽  
Vol 12 (9) ◽  
pp. 1454 ◽  
Author(s):  
Yong Zhang ◽  
Bin Yang ◽  
Zhengxian Yang ◽  
Guang Ye
Keyword(s):  
Pore Structure ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Mercury Intrusion Porosimetry ◽  
Cementitious Materials ◽  
Limestone Powder ◽  
Accurate Estimation ◽  
Mercury Intrusion ◽  
Pore Size Distributions

Capturing the long-term performance of concrete must be underpinned by a detailed understanding of the pore structure. Mercury intrusion porosimetry (MIP) is a widely used technique for pore structure characterization. However, it has been proven inappropriate to measure the pore size distribution of cementitious materials due to the ink-bottle effect. MIP with cyclic pressurization–depressurization can overcome the ink-bottle effect and enables a distinction between large (ink-bottle) pores and small (throat) pores. In this paper, pressurization–depressurization cycling mercury intrusion porosimetry (PDC-MIP) is adopted to characterize the pore structure in a range of cementitious pastes cured from 28 to 370 days. The results indicate that PDC-MIP provides a more accurate estimation of the pore size distribution in cementitious pastes than the standard MIP. Bimodal pore size distributions can be obtained by performing PDC-MIP measurements on cementitious pastes, regardless of the age. Water–binder ratio, fly ash and limestone powder have considerable influences on the formation of capillary pores ranging from 0.01 to 0.5 µm.

Hydraulic conductivity of clay mixed with nanomaterials

2015 ◽  
Vol 52 (6) ◽  
pp. 808-811 ◽  
Author(s):  
C.W.W. Ng ◽  
J.L. Coo
Keyword(s):  
Hydraulic Conductivity ◽  
Aluminum Oxide ◽  
Pore Size Distribution ◽  
Pore Size ◽  
Size Distribution ◽  
Mercury Intrusion Porosimetry ◽  
Flow Paths ◽  
Mercury Intrusion ◽  
Flexible Wall ◽  
Conductivity Behavior

The focus of this note is to investigate the hydraulic conductivity behavior of clay mixed with nanomaterials. Two different nanomaterials — namely, gamma-aluminum oxide powder (γ-Al2O3) and nano-copper oxide (CuO) — were selected and mixed with clay at different percentages (i.e., 2%, 4%, and 6%). Hydraulic conductivity tests were carried out in a flexible wall permeameter following the ASTM D5084 standard. Mercury intrusion porosimetry (MIP) tests were also carried out to determine the pore-size distribution. At 2% of γ-Al2O3 and nano-CuO, the hydraulic conductivity of clay decreased 30% and 45%, respectively. As the proportion of the nanomaterial increases, the reduction of hydraulic conductivity becomes less prominent as flow paths devoid of nanomaterials are unlikely. Reduction of hydraulic conductivity is due to the pores of clay being clogged by the nanomaterial. Pore-size distribution curves show that the largest pore size reduced by 20% when clay was mixed with 4% nano-CuO.

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