The Experts below are selected from a list of 300 Experts worldwide ranked by ideXlab platform
Allen G. Hunt - One of the best experts on this subject based on the ideXlab platform.
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improving Unsaturated Hydraulic Conductivity estimation in soils via percolation theory
Geoderma, 2017Co-Authors: Behzad Ghanbarian, Allen G. HuntAbstract:Accurate estimation of Unsaturated Hydraulic Conductivity K(Sw) in soils has been of great interest to soil physicists and hydrologists in the past several decades. Although various methods such as a “bundle of capillary tubes” conceptual approach were applied in the literature to theoretically model Hydraulic Conductivity in term of water saturation, in this study we invoke percolation theory, which quantifies the effect of the interconnectivity of pores on the macroscopic fluid flow. We incorporate the pore-solid interface roughness effect in the Hydraulic conductance-pore radius (g-r) relationship, evaluate our K(Sw) model using 104 soil samples from the UNSODA database as well as another 20 soil samples from the Rijtema database, and compare it to the Ghanbarian-Alavijeh and Hunt (2012) model. Generally speaking, we experimentally demonstrate that K(Sw) estimations were improved over the entire range of water saturation when the surface roughness effect was incorporated. However, our model still underestimates the Unsaturated Hydraulic Conductivity at low water saturations (corresponding to K(Sw) < 10− 4 cm/day). We show that after eliminating the effect of non-equilibrium conditions in the measurements K(Sw) estimations were improved substantially. Other plausible sources for K(Sw) underestimation are also discussed.
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Improving Unsaturated Hydraulic Conductivity estimation in soils via percolation theory
Geoderma, 2017Co-Authors: Behzad Ghanbarian, Allen G. HuntAbstract:Accurate estimation of Unsaturated Hydraulic Conductivity K(Sw) in soils has been of great interest to soil physicists and hydrologists in the past several decades. Although various methods such as a “bundle of capillary tubes” conceptual approach were applied in the literature to theoretically model Hydraulic Conductivity in term of water saturation, in this study we invoke percolation theory, which quantifies the effect of the interconnectivity of pores on the macroscopic fluid flow. We incorporate the pore-solid interface roughness effect in the Hydraulic conductance-pore radius (g-r) relationship, evaluate our K(Sw) model using 104 soil samples from the UNSODA database as well as another 20 soil samples from the Rijtema database, and compare it to the Ghanbarian-Alavijeh and Hunt (2012) model. Generally speaking, we experimentally demonstrate that K(Sw) estimations were improved over the entire range of water saturation when the surface roughness effect was incorporated. However, our model still underestimates the Unsaturated Hydraulic Conductivity at low water saturations (corresponding to K(Sw)
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Unsaturated Hydraulic Conductivity modeling for porous media with two fractal regimes
Geoderma, 2013Co-Authors: Allen G. Hunt, Behzad Ghanbarian, Kenneth C. SavilleAbstract:A reliable means to predict the saturation-dependence of the Hydraulic Conductivity would have important applications and implications across soil science. In our efforts to improve predictive capabilities we apply a bimodal pore size distribution to generate simultaneously the soil water retention curve (SWRC) and the Unsaturated Hydraulic Conductivity K in porous media. Our specific pore size model incorporates two fractal regimes, which we treat within the pore–solid fractal approach. The calculation of the Hydraulic Conductivity employs critical path analysis from percolation theory, which has already been shown to perform the best overall among models commonly employed. To evaluate the developed piecewise functions, 8 soil samples with different textures, e.g., loam, silt loam, sandy loam and clay are selected. All soils show almost the same cross-over point on both water retention and Hydraulic Conductivity curves on semi-log plots. We find that the piecewise water retention and Unsaturated Hydraulic Conductivity models fit well the measured data. However, the Hydraulic Conductivity curves predicted from the water retention data agree relatively well with the measured one just for the first regime and tend to underestimate K in the second. We also compare our results with those obtained from unimodal pore-size distribution reported by Ghanbarian-Alavijeh and Hunt (2012). Comparing the measured data with the unimodal and bimodal models indicates that the bimodal distribution provide somewhat more realistic predictions than the unimodal one. If prediction is sacrificed and we simply try to model K using our results, we find that we can generate a very accurate phenomenological description of K with only a slight change in the values of the fractal dimensionality. Reasons for this discrepancy are discussed.
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Unsaturated Hydraulic Conductivity in porous media: Percolation theory
Geoderma, 2012Co-Authors: Behzad Ghanbarian-alavijeh, Allen G. HuntAbstract:Abstract The Unsaturated Hydraulic Conductivity is an important property of porous media whose estimation is still investigated. In this study, we developed a new Unsaturated Hydraulic Conductivity model from applying percolation theory to the pore–solid fractal approach (PSF). In actual applications the pore size distribution was obtained from the soil water retention curve. Using 104 soil samples from the UNSODA data base, the new developed Unsaturated Hydraulic Conductivity model was compared with the Mualem's approach combined with water retention models of van Genuchten and PSF. The calculated root mean square error (RMSE) for the new model developed in this study, vG-M and PSF-M models was 0.69, 0.91 and 0.83 cm day− 1, respectively. The results showed that percolation theory model estimated Unsaturated Hydraulic Conductivity curve better than the vG-M and PSF-M models especially at high water contents.
Kristopher L. Kuhlman - One of the best experts on this subject based on the ideXlab platform.
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Unsaturated Hydraulic Conductivity models based on truncated lognormal pore-size distributions.
Ground water, 2014Co-Authors: Bwalya Malama, Kristopher L. KuhlmanAbstract:We develop a closed-form three-parameter model for Unsaturated Hydraulic Conductivity associated with the Kosugi three-parameter lognormal moisture retention model. The model derivation uses a slight modification to Mualem's theory, which is nearly exact for nonclay soils. Kosugi's three-parameter lognormal moisture retention model uses physically meaningful parameters, but a corresponding closed-form relative Hydraulic Conductivity model has never been developed. The model is further extended to a four-parameter model by truncating the underlying pore-size distribution at physically permissible minimum and maximum pore radii. The proposed closed-form models are fitted to well-known experimental data to illustrate their utility. They have the same physical basis as Kosugi's two-parameter model, but are more general.
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Unsaturated Hydraulic Conductivity Models Based on Truncated Lognormal Pore-Size
2014Co-Authors: Distributions Bwalya Malama, Kristopher L. KuhlmanAbstract:We develop a closed-form three-parameter model for Unsaturated Hydraulic Conductivity associated with the Kosugi three-parameter lognormal moisture retention model. The model derivation uses a slight modification to Mualem’s theory, which is nearly exact for nonclay soils. Kosugi’s three-parameter lognormal moisture retention model uses physically meaningful parameters, but a corresponding closed-form relative Hydraulic Conductivity model has never been developed. The model is further extended to a four-parameter model by truncating the underlying pore-size distribution at physically permissible minimum and maximum pore radii. The proposed closed-form models are fitted to well-known experimental data to illustrate their utility. They have the same physical basis as Kosugi’s two-parameter model, but are more general.
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Models for Unsaturated Hydraulic Conductivity Based on Truncated Lognormal Pore-size Distributions.
Journal of Hydrology, 2012Co-Authors: Bwalya Malama, Kristopher L. KuhlmanAbstract:Abstract We develop a closed-form three-parameter model for Unsaturated Hydraulic Conductivity associated with a three-parameter lognormal model of moisture retention, which is based on lognormal grainsize distribution. The derivation of the model is made possible by a slight modification to the theory of Mualem. We extend the three-parameter lognormal distribution to a four-parameter model that also truncates the pore size distribution at a minimum pore radius. We then develop the corresponding four-parameter model for moisture retention and the associated closed-form expression for Unsaturated Hydraulic Conductivity. The four-parameter model is fitted to experimental data, similar to the models of Kosugi and van Genuchten. The proposed four-parameter model retains the physical basis of Kosugi’s model, while improving fit to observed data especially when simultaneously fitting pressure-saturation and pressure-Conductivity data.
A S Gregory - One of the best experts on this subject based on the ideXlab platform.
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investigating the relationship between Unsaturated Hydraulic Conductivity curve and confined compression curve
Journal of Hydrology, 2015Co-Authors: Hossein Bayat, Azadeh Sedaghat, Ali Akbar Safari Sinegani, A S GregoryAbstract:Summary This study was conducted to estimate the soil Unsaturated Hydraulic Conductivity through the van Genuchten model using easy to measure soil properties by regression and artificial neural networks methods. In this study, 148 soil samples were taken from five provinces of Iran. Basic soil properties (clay, silt/sand and bulk density) and other soil properties were measured. Soil water retention curve was measured to obtain the Unsaturated Hydraulic Conductivity curve using the van Genuchten–Mualem model. Confined compression curve was measured and the modified model of van Genuchten was fitted on its data. Two-thirds and one-third of the data were used for the training and testing steps, respectively. Confined compression curve parameters and other soil properties were used as predictors to estimate Unsaturated Hydraulic Conductivity curve. Pedotransfer functions (PTFs) were developed in two separate parts: in 5 and 6 PTFs basic soil properties were or were not used as predictors, respectively. The artificial neural networks (ANNs) performed better than the regression methods. Among the ANN-developed PTFs which have not used basic soil properties as predictors, PTFa3, with the inputs of the parameters of confined compression curve (n∗, α∗ and e0), performed better than the others. Also, among the ANN-developed PTFs that used basic soil properties as predictors along with the other input variables, PTFb5 that used the σmc (stress at the maximum curvature) and σi (stress at the inflection point) as inputs along with basic soil properties, performed better than the other PTFs. The results showed a successful prediction of the Hydraulic Conductivity curve using confined compression curve.
Yu-jun Cui - One of the best experts on this subject based on the ideXlab platform.
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Unsaturated Hydraulic Conductivity of Highly Compacted Sand-GMZ01 Bentonite Mixtures Under Confined Conditions
Engineering Geology for Society and Territory - Volume 6, 2014Co-Authors: Miao Shen, Yong-gui Chen, Yu-jun CuiAbstract:Highly compacted sand-bentonite mixtures are commonly recognized as potential buffer/backfill materials using in deep geological repository for high-level radioactive waste disposals. After water retention curve was determined, instantaneous profile method was employed in this paper for measuring Unsaturated Hydraulic Conductivity of highly compacted GMZ01 bentonite and quartz sand mixture (7:3), with a dry density of 1.90 g/cm3, under confined conditions. Results show that, as suction decreased from 60 MPa to zero, the measured Unsaturated Hydraulic Conductivity firstly decreased and then turned to increase. This phenomenon can be explained in terms of microstructure changes during hydration under constant-volume conditions.
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An Unsaturated Hydraulic Conductivity model for compacted GMZ01 bentonite with consideration of temperature
Environmental Earth Sciences, 2014Co-Authors: Min Wan, Bao Chen, Yong-gui Chen, Yu-jun Cui, Ju WangAbstract:As one of the most important properties of compacted bentonite used as buffer/backfill materials, Hydraulic Conductivity is influenced by various factors including temperature, microstructure and suction (or degree of saturation), etc. Based on the readily available results of both temperature-controlled water-retention tests and Unsaturated infiltration tests under confined (constant volume) conditions, influences of temperature and microstructure variations on Unsaturated Hydraulic Conductivity of the compacted Gaomiaozi (GMZ01) bentonite were analyzed. Then, a revised Unsaturated Hydraulic Conductivity model considering temperature effects and microstructure changes was developed. With this proposed model, prediction and comparison were made on the Unsaturated Hydraulic Conductivity of the compacted GMZ01 bentonite at 20 A degrees C. Results show that water-retention capacity of compacted GMZ01 bentonite decreases as temperature increases and the degree of the temperature influence depends on suction. Under confined conditions, influence of hydration on microstructure of compacted GMZ01 bentonite depends on pore size. The proposed model can well describe the variations of Unsaturated Hydraulic Conductivity with suction at different temperatures. However, further improvement of the proposed model is needed to account for the phenomenon of inter-aggregate pores clogging that occurred at the initial stage of hydration of compacted GMZ01 bentonite under confined conditions.
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An Unsaturated Hydraulic Conductivity model for compacted GMZ01 bentonite with consideration of temperature
Environmental Earth Sciences, 2013Co-Authors: Min Wan, Bao Chen, Yong-gui Chen, Yu-jun Cui, Ju WangAbstract:As one of the most important properties of compacted bentonite used as buffer/backfill materials, Hydraulic Conductivity is influenced by various factors including temperature, microstructure and suction (or degree of saturation), etc. Based on the readily available results of both temperature-controlled water-retention tests and Unsaturated infiltration tests under confined (constant volume) conditions, influences of temperature and microstructure variations on Unsaturated Hydraulic Conductivity of the compacted Gaomiaozi (GMZ01) bentonite were analyzed. Then, a revised Unsaturated Hydraulic Conductivity model considering temperature effects and microstructure changes was developed. With this proposed model, prediction and comparison were made on the Unsaturated Hydraulic Conductivity of the compacted GMZ01 bentonite at 20 °C. Results show that water-retention capacity of compacted GMZ01 bentonite decreases as temperature increases and the degree of the temperature influence depends on suction. Under confined conditions, influence of hydration on microstructure of compacted GMZ01 bentonite depends on pore size. The proposed model can well describe the variations of Unsaturated Hydraulic Conductivity with suction at different temperatures. However, further improvement of the proposed model is needed to account for the phenomenon of inter-aggregate pores clogging that occurred at the initial stage of hydration of compacted GMZ01 bentonite under confined conditions.
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Determining the Unsaturated Hydraulic Conductivity of a compacted sand-bentonite mixture under constant volume and free-swell conditions
Physics and Chemistry of The Earth, 2008Co-Authors: Yu-jun Cui, Anh Minh Tang, Cyril Loiseau, Pierre DelageAbstract:Highly compacted sand-bentonite mixtures are often considered as possible engineered barriers in deep high-level radioactive waste disposals. In-situ, the saturation of these barriers from their initially Unsaturated state is a complex hydro-mechanical coupled process in which temperature effects also play a role. The key parameter of this process is the Unsaturated Hydraulic Conductivity of the barrier. In this paper, isothermal infiltration experiments were conducted to determine the Unsaturated Hydraulic Conductivity according to the instantaneous profile method. To do so, total suction changes were monitored at different locations along the soil specimen by using resistivity relative humidity probes. Three constant volume infiltration tests were conducted showing, unexpectedly, a decrease of the Hydraulic Conductivity during infiltration. One test performed under free-swell conditions showed the opposite and standard trend. These observations were interpreted in terms of microstructure changes during wetting, both under constant volume and free swell conditions.
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Determining the Unsaturated Hydraulic Conductivity of a compacted sand-bentonite mixture under constant-volume and free-swell conditions
Physics and Chemistry of the Earth Parts A B C, 2008Co-Authors: Yu-jun Cui, Anh Minh Tang, Cyril Loiseau, Pierre DelageAbstract:Abstract Highly compacted sand–bentonite mixtures are often considered as possible engineered barriers in deep high-level radioactive waste disposals. In situ, the saturation of these barriers from their initially Unsaturated state is a complex hydro-mechanical coupled process in which temperature effects also play a role. The key parameter of this process is the Unsaturated Hydraulic Conductivity of the barrier. In this paper, isothermal infiltration experiments were conducted to determine the Unsaturated Hydraulic Conductivity according to the instantaneous profile method. To do so, total suction changes were monitored at different locations along the soil specimen by using resistive relative humidity probes. Three constant-volume infiltration tests were conducted showing, unexpectedly, a decrease of the Hydraulic Conductivity during infiltration. One test performed under free-swell conditions showed the opposite and standard trend. These observations were interpreted in terms of microstructure changes during wetting, both under constant-volume and free-swell conditions.
Hossein Bayat - One of the best experts on this subject based on the ideXlab platform.
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investigating the relationship between Unsaturated Hydraulic Conductivity curve and confined compression curve
Journal of Hydrology, 2015Co-Authors: Hossein Bayat, Azadeh Sedaghat, Ali Akbar Safari Sinegani, A S GregoryAbstract:Summary This study was conducted to estimate the soil Unsaturated Hydraulic Conductivity through the van Genuchten model using easy to measure soil properties by regression and artificial neural networks methods. In this study, 148 soil samples were taken from five provinces of Iran. Basic soil properties (clay, silt/sand and bulk density) and other soil properties were measured. Soil water retention curve was measured to obtain the Unsaturated Hydraulic Conductivity curve using the van Genuchten–Mualem model. Confined compression curve was measured and the modified model of van Genuchten was fitted on its data. Two-thirds and one-third of the data were used for the training and testing steps, respectively. Confined compression curve parameters and other soil properties were used as predictors to estimate Unsaturated Hydraulic Conductivity curve. Pedotransfer functions (PTFs) were developed in two separate parts: in 5 and 6 PTFs basic soil properties were or were not used as predictors, respectively. The artificial neural networks (ANNs) performed better than the regression methods. Among the ANN-developed PTFs which have not used basic soil properties as predictors, PTFa3, with the inputs of the parameters of confined compression curve (n∗, α∗ and e0), performed better than the others. Also, among the ANN-developed PTFs that used basic soil properties as predictors along with the other input variables, PTFb5 that used the σmc (stress at the maximum curvature) and σi (stress at the inflection point) as inputs along with basic soil properties, performed better than the other PTFs. The results showed a successful prediction of the Hydraulic Conductivity curve using confined compression curve.
