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Journal articles on the topic 'Unsaturated hydraulic conductivity'

Author: Grafiati

Published: 4 June 2021

Last updated: 31 January 2023

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1

Li, X., L. M. Zhang, and D. G. Fredlund. "Wetting front advancing column test for measuring unsaturated hydraulic conductivity." Canadian Geotechnical Journal 46, no. 12 (December 2009): 1431–45. http://dx.doi.org/10.1139/t09-072.

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Unsaturated hydraulic conductivity is the primary soil parameter required when performing seepage analyses for unsaturated–saturated soil systems. Unsaturated hydraulic conductivity is also one of the most difficult parameters to measure because of the time involved and the limited suction measurement range (e.g., 0∼1500 kPa in a test using the steady-state method). In this study, a new wetting front advancing method was developed for measuring unsaturated hydraulic conductivity. The wetting front advancing method simulates and monitors a soil wetting process through a large-scale soil column. A new interpretative procedure was developed to calculate the unsaturated hydraulic conductivity based on the monitored water content, suction, and wetting front advancing velocity. The proposed technique is used to measure the unsaturated hydraulic conductivities of five soils, which vary from gravel to clay. The results indicate that the proposed technique is time-saving (i.e., requires several days for a complete test) and is applicable over wide ranges of suctions and unsaturated hydraulic conductivities. The measured unsaturated hydraulic conductivity using the wetting front advancing method is similar to that obtained using the instantaneous profile method, with the latter covering narrower ranges of soil suction and hydraulic conductivity.

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2

Singh, D. N., and Sneha J. Kuriyan. "Estimation of hydraulic conductivity of unsaturated soils using a geotechnical centrifuge." Canadian Geotechnical Journal 39, no. 3 (June 1, 2002): 684–94. http://dx.doi.org/10.1139/t02-013.

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A saturated silty soil sample is centrifuged in a geotechnical centrifuge to create an unsaturated state. The change in water content of the soil sample is recorded at different points along the length of the sample to obtain the water-content profile, which is then used to obtain the unsaturated hydraulic conductivity of the soil sample. These hydraulic conductivity values are compared with those obtained and reported by previous researchers by conducting accelerated falling-head tests on this soil sample in a centrifuge. The study demonstrates the use of centrifugation techniques to obtain hydraulic conductivities of unsaturated soils.Key words: silty soil, saturated soil, unsaturated soil, hydraulic conductivity, centrifuge testing.

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3

Holland, D. F., M. Yitayew, and A. W. Warrick. "Measurement of Subsurface Unsaturated Hydraulic Conductivity." Journal of Irrigation and Drainage Engineering 126, no. 1 (January 2000): 21–27. http://dx.doi.org/10.1061/(asce)0733-9437(2000)126:1(21).

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4

OTHMER, HEINRICH, BERND DIEKKRÜGER, and MIROSLAV KUTILEK. "BIMODAL POROSITY AND UNSATURATED HYDRAULIC CONDUCTIVITY." Soil Science 152, no. 3 (September 1991): 139–50. http://dx.doi.org/10.1097/00010694-199109000-00001.

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5

Schwaerzel, K., and H. P. Bohl. "An easily installable groundwater lysimeter to determine waterbalance components and hydraulic properties of peat soils." Hydrology and Earth System Sciences 7, no. 1 (February 28, 2003): 23–32. http://dx.doi.org/10.5194/hess-7-23-2003.

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Abstract. A simple method for the installation of groundwater lysimeters in peat soils was developed which reduces both time and financial effort significantly. The method was applied on several sites in the Rhinluch, a fen peat land 60 km northwest of Berlin, Germany. Over a two-year period, upward capillary flow and evapotranspiration rates under grassland with different groundwater levels were measured. The installation of tensiometers and TDR probes additionally allowed the in situ determination of the soil hydraulic properties (water retention and unsaturated hydraulic conductivity). The results of the measurements of the unsaturated hydraulic conductivity demonstrate that more than one single method has to be applied if the whole range of the conductivity function from saturation to highly unsaturated is to be covered. Measuring the unsaturated conductivity can be done only in the lab for an adequately wide range of soil moisture conditions. Keywords: peat soils, soil hydraulic properties, evapotranspiration, capillary flow, root distribution, unsaturated zone

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6

Villagra-Mendoza, Karolina, and Rainer Horn. "Effect of biochar on the unsaturated hydraulic conductivity of two amended soils." International Agrophysics 32, no. 3 (July 1, 2018): 373–78. http://dx.doi.org/10.1515/intag-2017-0025.

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Abstract Water and solute transports in the vadose zone depend on the distribution, size, shape and configuration of the pores. They affect the soil hydraulic properties and, consequently, the directly related processes such as water storage, infiltration, groundwater recharge, and also erosion and runoff. Soils amended with biochar are prompt to improve their physical and hydraulic properties. Biochar addition alters not only porosity, the water retention pattern and the derived pore distribution, but also the hydraulic conductivity under saturated and unsaturated conditions. In our work, two different doses (2.5 and 5% dry wt.) were added to two textured soils (sand and sandy loam). The unsaturated hydraulic conductivity and saturated hydraulic conductivity were measured under laboratory conditions. The obtained results show the positive effect of biochar on the hydraulic functions. For the sandy soil, the higher the dose of biochar, the more constant and relatively higher is the hydraulic conductivity up to - 40 kPa. At less negative matric potentials (< -10 kPa), the unamended sandy loam soil showed a slightly higher unsaturated hydraulic conductivity, compared to the amended soils. These results underline that biochar addition enhances the transport of water under unsaturated conditions by reducing the formation of larger pores while also intensifying the finer inter-particle pore formation.

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7

Singh, D. N., and Sneha J. Kuriyan. "Estimation of unsaturated hydraulic conductivity using soil suction measurements obtained by an insertion tensiometer." Canadian Geotechnical Journal 40, no. 2 (April 1, 2003): 476–83. http://dx.doi.org/10.1139/t02-112.

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To estimate the unsaturated soil hydraulic conductivity of a silty soil, an insertion tensiometer has been used for measuring its suction corresponding to different water contents. These suction values have been used for developing the soil-water characteristic curve (SWCC). The obtained SWCC has been compared with the trends predicted by various fits available in the literature. Further, with the help of the obtained SWCC, the unsaturated soil hydraulic conductivity has been estimated. The study demonstrates the usefulness of insertion tensiometers for measuring soil suction and for estimating its hydraulic conductivity.Key words: silty soil, suction, insertion tensiometer, soil-water characteristic curve, unsaturated soil hydraulic conductivity.

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8

McDougall, J. R., and I. C. Pyrah. "Simulating transient infiltration in unsaturated soils." Canadian Geotechnical Journal 35, no. 6 (December 1, 1998): 1093–100. http://dx.doi.org/10.1139/t98-059.

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Transient responses to various infiltration events have been examined using an unsaturated flow model. Numerical simulations reveal a range of infiltration patterns which can be related to the ratio of infiltration rate to unsaturated hydraulic conductivity. A high value of this ratio reflects a prevailing hydraulic conductivity which cannot readily redistribute the newly infiltrated moisture. Moisture accumulates in the near-surface region before advancing down through the soil as a distinct wetting front. In contrast, low values of the ratio of rainfall to unsaturated hydraulic conductivity show minimal moisture accumulation, as the relatively small volumes of infiltrating moisture are readily redistributed through the soil profile.Key words: numerical modelling, infiltration, unsaturated soil, soil suction, groundwater.

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9

Tao, Gaoliang, Xueliang Zhu, Jianchao Cai, Henglin Xiao, Qingsheng Chen, and Yin Chen. "A Fractal Approach for Predicting Unsaturated Hydraulic Conductivity of Deformable Clay." Geofluids 2019 (May 2, 2019): 1–9. http://dx.doi.org/10.1155/2019/8013851.

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The relative hydraulic conductivity is one of the key parameters for unsaturated soils in numerous fields of geotechnical engineering. The quantitative description of its variation law is of significant theoretical and technical values. Parameters in a classical hydraulic conductivity model are generally complex; it is difficult to apply these parameters to predict and estimate the relative hydraulic conductivity under deformation condition. Based on the fractal theory, a simple method is presented in this study for predicting the relative hydraulic conductivity under deformation condition. From the experimental soil-water characteristic curve at a reference state, the fractal dimension and air-entry value are determined at a reference state. By using the prediction model of air-entry value, the air-entry values at the deformed state are then determined. With the two parameters determined, the relative hydraulic conductivity at the deformed state is predicted using the fractal model of relative hydraulic conductivity. The unsaturated hydraulic conductivity of deformable Hunan clay is measured by the instantaneous profile method. Values of relative hydraulic conductivity predicted by the fractal model are compared with those obtained from experimental measurements, which proves the rationality of the proposed prediction method.

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10

Song, Young-Suk. "Estimation on Unsaturated Hydraulic Conductivity Function of Jumoonjin Sand for Various Relative Densities." Journal of the Korean Society of Civil Engineers 33, no. 6 (2013): 2369. http://dx.doi.org/10.12652/ksce.2013.33.6.2369.

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11

Wang, Ji-Peng, Pei-Zhi Zhuang, Ji-Yuan Luan, Tai-Heng Liu, Yi-Ran Tan, and Jiong Zhang. "Estimation of Unsaturated Hydraulic Conductivity of Granular Soils from Particle Size Parameters." Water 11, no. 9 (August 31, 2019): 1826. http://dx.doi.org/10.3390/w11091826.

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Estimation of unsaturated hydraulic conductivity could benefit many engineering or research problems such as water flow in the vadose zone, unsaturated seepage and capillary barriers for underground waste isolation. The unsaturated hydraulic conductivity of a soil is related to its saturated hydraulic conductivity value as well as its water retention behaviour. By following the first author’s previous work, the saturated hydraulic conductivity and water retention curve (WRC) of sandy soils can be estimated from their basic gradation parameters. In this paper, we further suggest the applicable range of the estimation method is for soils with d10 > 0.02mm and Cu < 20, in which d10 is the grain diameter corresponding to 10% passing and Cu is the coefficient of uniformity (Cu=d60d10). The estimation method is also modified to consider the porosity variation effect. Then the proposed method is applied to predict unsaturated hydraulic conductivity properties of different sandy soils and also compared with laboratory and field test results. The comparison shows that the newly developed estimation method, which predicts the relative permeability of unsaturated sands from basic grain size parameters and porosity, generally has a fair agreement with measured data. It also indicates that the air-entry value is mainly relative to the mean grain size and porosity value change from the intrinsic value. The rate of permeability decline with suction is mainly associated with grain size polydispersity.

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12

Alzaidy, Mohammed Nawaf Jirjees. "A Theoretical Study of Some Unsaturated Properties for Different Soils." Journal of University of Babylon for Engineering Sciences 26, no. 9 (November 1, 2018): 149–65. http://dx.doi.org/10.29196/jubes.v26i9.1720.

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Soil–water characteristic curves (SWCC) can be defined as the relationship between the water content and suction of an unsaturated soil. It considered a basic relation to explanation of the engineering behaviour of unsaturated soil such as hydraulic conductivity and shear strength, So the study of SWCC is useful to reduce the time and cost of unsaturated soil testing for different engineering purposes. An approach model has been used to predict the SWCC for different soils. The influence of the soils on SWCC shape, the unsaturated hydraulic conductivity and shear strength parameters have been studied in this paper using mathematical models. The results of SWCC show that suction of clay soil is bigger than sandy soil, while the clayey silt soils exhibit an intermediate behaviour at same water content. The values of unsaturated shear strength are increasing while the unsaturated hydraulic conductivity is decreasing with increasing soil suction. This behaviour of the last two parameters with soil suction should be taken in consideration for engineering purposes.

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13

Fields, Jeb S., James S. Owen, and Holly L. Scoggins. "The Influence of Substrate Hydraulic Conductivity on Plant Water Status of an Ornamental Container Crop Grown in Suboptimal Substrate Water Potentials." HortScience 52, no. 10 (October 2017): 1419–28. http://dx.doi.org/10.21273/hortsci11987-17.

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Many soilless substrates are inefficient with regard to water (i.e., high porosity and low water holding capacity), which provides an excellent opportunity to increase water efficiency in containerized production. We suggest that increasing hydraulic conductivity in the dry range of substrate moisture content occurring during production can increase water availability, reduce irrigation volume, and produce high quality, marketable crops. Three substrates were engineered using screened pine bark (PB) and amending with either Sphagnum peatmoss or coir to have higher unsaturated hydraulic conductivity between water potentials of −100 and −300 hPa. There was no correlation between substrate unsaturated hydraulic conductivity and saturated hydraulic conductivity (r = 0.04, P = 0.8985). Established Hydrangea arborescens (L.) ‘Annabelle’ plants were grown in the three engineered and a conventional (control) PB substrates exposed to suboptimal irrigation levels (i.e., held at substrate water potentials between −100 and −300 hPa) for 32 days. The plants in the engineered substrates outperformed the control in every growth and morphological metric measured, as well as exhibiting fewer (or no) physiological drought stress indicators (i.e., vigor, growth, plant development, etc.) compared with the control. We observed increased vigor measures in plants grown in substrates with higher unsaturated hydraulic conductivity, as well as greater plant water uptake. The coir increased unsaturated hydraulic conductivity and provided an increased air space when incorporated into coarse bark vs. if peat was incorporated into bark at the same ratio by volume. Increasing PB hydraulic conductivity, through screening bark or amending bark with fibrous materials, in concert with low irrigations can produce marketable, vigorous crops while reducing water consumed and minimizing water wasted in ornamental container production.

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14

Rojas, Jhan Piero, Juan Carlos Ruge, and Gustavo Adolfo Carrillo. "Unsaturated Hydraulic Conductivity in Composite Porous Media." Applied Sciences 12, no. 18 (September 9, 2022): 9058. http://dx.doi.org/10.3390/app12189058.

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Determining the constitutive properties that describe the incipient hydraulic behavior of the materials, including the matrix domains and the distribution of macro and micropores, is crucial to analyzing the preferential water flow in saturated soils, ks, and unsaturated, ku. This study focused on determining the hydraulic conductivity in porous media under total and partial saturation conditions. The infiltration characteristics of three reconstituted soils were evaluated using five suction ranges employing conventional permeameters, an automated dual system, and mini-disk infiltrometers. The experimental cycles were carried out in granular soils with mixtures of diatomaceous soils, iron oxide (Fe2O3), and calcium carbonate (CaCO3) in 5–40% proportions. The differences between the granular microstructures of each material and the different hydraulic interaction mechanisms (suctione levels) significantly affected the values of ks and ku and the coupling between the pore domains and the defined water regime. Additionally, a lower impact was observed in the data set exposed to higher percentages of Fe2O3 and CaCO3 in different suction ranges, mainly due to a tension effect (meniscus) generated by suction in the granular skeleton. Since both parameters are mutually correlated and have a similar impact between methods and soil cores, ks and ku must be optimized simultaneously in each mechanism analyzed. The main findings of this work result in the confirmation that the unsaturated permeability decreases as suction is imposed on the sample. As well as the addition of different materials with Particle Size Distribution finer than the base sample, it also reveals a reduction in hydraulic conductivity, both saturated and unsaturated.

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15

Burés, S., O. Marfà, T. Pérez, J. Tébar, and A. Lloret. "MEASURE OF SUBSTRATES UNSATURATED HYDRAULIC CONDUCTIVITY (REFEREED)." Acta Horticulturae, no. 450 (July 1997): 297–304. http://dx.doi.org/10.17660/actahortic.1997.450.35.

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16

SUGIE, Shinsuke, and Renji NARUSE. "Measurements of unsaturated hydraulic conductivity of snow." Journal of the Japanese Society of Snow and Ice 62, no. 2 (2000): 117–27. http://dx.doi.org/10.5331/seppyo.62.117.

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17

Tuller, Markus, and Dani Or. "Unsaturated Hydraulic Conductivity of Structured Porous Media." Vadose Zone Journal 1, no. 1 (2002): 14. http://dx.doi.org/10.2136/vzj2002.0014.

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18

Alexander, Lynne, and R. Wayne Skaggs. "Predicting Unsaturated Hydraulic Conductivity from Soil Texture." Journal of Irrigation and Drainage Engineering 113, no. 2 (May 1987): 184–97. http://dx.doi.org/10.1061/(asce)0733-9437(1987)113:2(184).

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19

Samani, Zohrab A., and L. S. Willardson. "Simple Laboratory Measurement of Unsaturated Hydraulic Conductivity." Journal of Irrigation and Drainage Engineering 113, no. 3 (August 1987): 405–12. http://dx.doi.org/10.1061/(asce)0733-9437(1987)113:3(405).

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20

Williams, J. D., J. P. Dobrowolski, and N. E. West. "Microbiotic Crust Influence on Unsaturated Hydraulic Conductivity." Arid Soil Research and Rehabilitation 13, no. 2 (January 1999): 145–54. http://dx.doi.org/10.1080/089030699263384.

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21

Yeh, T. C. Jim, and Donald J. Harvey. "Effective unsaturated hydraulic conductivity of layered sands." Water Resources Research 26, no. 6 (June 1990): 1271–79. http://dx.doi.org/10.1029/wr026i006p01271.

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22

Poulsen, T. G., P. Moldrup, and O. H. Jacobsen. "ONE-PARAMETER MODELS FOR UNSATURATED HYDRAULIC CONDUCTIVITY." Soil Science 163, no. 6 (June 1998): 425–35. http://dx.doi.org/10.1097/00010694-199806000-00001.

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23

Zhao, Tian Yu, Hu Yuan Zhang, and Chen Xiang Yu. "Soil-Water Characteristics of Saline Soil in Northwest China." Advanced Materials Research 487 (March 2012): 548–52. http://dx.doi.org/10.4028/www.scientific.net/amr.487.548.

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Geotechnical engineers have become increasingly aware of salt damages caused by water-salt migration.The soil water characteristic curve (SWCC) is a very important tool for determining the engineering properties of unsaturated soil. Using pressure plate extractors, This paper carried out a research on soil-water characteristics of saline soil in northwest China. Then, The relationship between matrix suction and water content was analyzed, the unsaturated hydraulic conductivity in different water content was calculated through predicting model of Van Genuchten(1980). Based on the measurement and calculation, the correlation between unsaturated hydraulic conductivity and water content was established. Research results show that unsaturated hydraulic conductivity of saline soil decreases in non-linear trend with the water content reducing, while it decline linearly by a certain specific rate with the matrix suction increasing at a high-suction section (100kpa ~ 100000kpa) in double logarithmic coordinates.

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24

Simms, P. H., and E. K. Yanful. "A pore-network model for hydromechanical coupling in unsaturated compacted clayey soils." Canadian Geotechnical Journal 42, no. 2 (April 1, 2005): 499–514. http://dx.doi.org/10.1139/t05-002.

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The behaviour of deformable unsaturated soils is difficult to characterize with simple relationships. Unsaturated hydraulic properties, namely the soil-water characteristic curve and the hydraulic conductivity function, are dependent on both volume change and degree of saturation, whereas volume change itself often cannot be related to a single stress variable but must be described by independent functions of mechanical loading and suction. It is proposed that a means to obtain these functions is through pore-network modelling, by which it is possible to integrate the phenomena of drainage and volume change and the different effects of suction and mechanical loading. The implementation of a two-dimensional pore-network model is described. A simple algorithm for individual pore volume change is adopted. The model uses pore-size distributions measured by mercury intrusion porosimetry to initially generate the simulated pore grid. Predictions of soil-water characteristic curves, void ratio versus suction curves, pore-size distributions at specific suctions, unsaturated hydraulic conductivity, and compression curves are compared with measured values from two compacted clayey soils.Key words: unsaturated soil, volume change, pore network, soil-water characteristic curve, unsaturated hydraulic conductivity, compacted clay.

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25

Codevilla, Mauro, Camilo Casagrande, Marcos Montoro, Sandra Orlandi, Teresa Piqué, and Diego Manzanal. "Evaluation of sand-clay-anionic polyacrylamide blends for alternative compacted clay landfill liner design." MATEC Web of Conferences 337 (2021): 04002. http://dx.doi.org/10.1051/matecconf/202133704002.

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In this project, an innovative low hydraulic conductivity material for landfill cover and liner construction was studied. The material is a blend of natural clayey soil from Comodoro Rivadavia city (Chubut province, Argentina) mixed with fine uniform sand and anionic polyacrylamide (APAM). The research emphasizes understanding the influence of APAM addition on the soil water retention capacity (SWRC), unsaturated hydraulic conductivity, and swelling behavior. APAM is a super absorbent polymer that swells when immersed in water. SWRC was evaluated through the filter paper method. The unsaturated hydraulic conductivity and swelling behavior were determined using two fluids: distilled water and brine (C = 2 M). Results showed that APAM addition reduced the blends' microporosity, increased the water retention capacity, and reduced the hydraulic conductivity of the system. These promising results encourage further research on these blends' behavior to determine the most efficient blend formulation to enhance its hydro-mechanical performance and its chemical compatibility with landfill leachates for cover and low hydraulic conductivity liner layer construction.

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26

Stoffregen, Heiner, and Gerd Wessolek. "Scaling the Hydraulic Functions of A Water Repellent Sandy Soil." International Agrophysics 28, no. 3 (July 29, 2014): 349–58. http://dx.doi.org/10.2478/intag-2014-0025.

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Abstract The heterogeneity of both unsaturated hydraulic conductivity and water retention was measured with a high spatial resolution on a transect using an evaporation method. Fifteen undisturbed 100 cm3 soil cores were taken on a transect every 10 cm from the topsoil of a water repellent sandy site. Five dynamic water retention curves and four unsaturated conductivity curves were determined for each core. We conducted measurements without further saturation in the laboratory in order to achieve field-like conditions. The initial water contents were heterogeneous, indicating different hysteretic conditions and water repellent areas. The scattering of the water retention curves was high, while the heterogeneity of unsaturated conductivity curves was unexpectedly low. Two scaling approaches were used to describe the heterogeneity: one with and one without considering hysteresis. The concept of scaling applies well to describing the heterogeneity of both hydraulic functions. Including hysteresis leads to similar results than excluding hysteresis. The distribution of the hydraulic conductivity and the water retention were independent from each other. The results give important information for numerical simulation of the water flow with heterogeneous hydraulic functions.

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27

Yunjin, Hu, Su Baoyu, and Mao Genhai. "An experimental approach for determining unsaturated hydraulic properties of rock fractures." Hydrology Research 35, no. 3 (June 1, 2004): 251–60. http://dx.doi.org/10.2166/nh.2004.0018.

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An experimental approach for determining the unsaturated hydraulic properties (the relations between capillary pressure, saturation and unsaturated hydraulic conductivity) of rock fractures is developed and tested. Applying this approach to a single fracture, and with only water flowing, the capillary pressure–saturation and unsaturated hydraulic conductivity–capillary pressure relationships of the fracture during drainage and imbibition can be determined simultaneously. To facilitate the test of the validity of the experimental approach and to elucidate the characteristics of water flow in unsaturated fractures, an analogous fracture with parallel, connected channels of different apertures was fabricated. Experiments of unsaturated water flow in the analogous fracture were carried out. Some characteristics of water flow in unsaturated fractures (hysteresis between drainage and imbibition, etc.) were elucidated. Comparison of measured saturation values and theoretical saturation values corresponding to different apertures at the beginning of drainage and imbibition shows that the experimental approach presented in this paper is valid.

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28

Pichault, M., E. Beckers, A. Degré, and S. Garré. "Characterization of stony soils' hydraulic conductivity using laboratory and numerical experiments." SOIL Discussions 2, no. 2 (October 29, 2015): 1103–33. http://dx.doi.org/10.5194/soild-2-1103-2015.

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Abstract. Determining soil hydraulic properties is of major concern in various fields of study. Though stony soils are widespread across the globe, most studies deal with gravel-free soils so that the literature describing the impact of stones on soil's hydraulic conductivity is still rather scarce. Most frequently, models characterizing the saturated hydraulic conductivity of stony soils assume that the only effect of rock fragments is to reduce the volume available for water flow and therefore they predict a decrease in hydraulic conductivity with an increasing stoniness. The objective of this study is to assess the effect of rock fragments on the saturated and unsaturated hydraulic conductivity. This was done by means of laboratory and numerical experiments involving different amounts and types of coarse fragments. We compared our results with values predicted by the aforementioned models. Our study suggests that considering that stones only reduce the volume available for water flow might be ill-founded. We pointed out several drivers of the saturated hydraulic conductivity of stony soils, not considered by these models. On the one hand, the shape and the size of inclusions may substantially affect the hydraulic conductivity. On the other hand, the presence of rock fragments can counteract and even overcome the effect of a reduced volume in some cases. We attribute this to the creation of voids at the fine earth-stone interface. Nevertheless, these differences are mainly important near to saturation. However, we come up with a more nuanced view regarding the validity of the models under unsaturated conditions. Indeed, under unsaturated conditions, the models seem to represent the hydraulic behaviour of stones reasonably well.

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29

Rezanezhad, F., W. L. Quinton, J. S. Price, D. Elrick, T. R. Elliot, and R. J. Heck. "Examining the effect of pore size distribution and shape on flow through unsaturated peat using 3-D computed tomography." Hydrology and Earth System Sciences Discussions 6, no. 3 (May 15, 2009): 3835–62. http://dx.doi.org/10.5194/hessd-6-3835-2009.

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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.

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30

Chen, Tian, Mao Du, and Qiangling Yao. "Evolution of Hydraulic Conductivity of Unsaturated Compacted Na-Bentonite under Confined Condition—Including the Microstructure Effects." Materials 15, no. 1 (December 28, 2021): 219. http://dx.doi.org/10.3390/ma15010219.

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Compacted bentonite is envisaged as engineering buffer/backfill material in geological disposal for high-level radioactive waste. In particular, Na-bentonite is characterised by lower hydraulic conductivity and higher swelling competence and cation exchange capacity, compared with other clays. A solid understanding of the hydraulic behaviour of compacted bentonite remains challenging because of the microstructure expansion of the pore system over the confined wetting path. This work proposed a novel theoretical method of pore system evolution of compacted bentonite based on its stacked microstructure, including the dynamic transfer from micro to macro porosity. Furthermore, the Kozeny–Carman equation was revised to evaluate the saturated hydraulic conductivity of compacted bentonite, taking into account microstructure effects on key hydraulic parameters such as porosity, specific surface area and tortuosity. The results show that the prediction of the revised Kozeny–Carman model falls within the acceptable range of experimental saturated hydraulic conductivity. A new constitutive relationship of relative hydraulic conductivity was also developed by considering both the pore network evolution and suction. The proposed constitutive relationship well reveals that unsaturated hydraulic conductivity undergoes a decrease controlled by microstructure evolution before an increase dominated by dropping gradient of suction during the wetting path, leading to a U-shaped relationship. The predictive outcomes of the new constitutive relationship show an excellent match with laboratory observation of unsaturated hydraulic conductivity for GMZ and MX80 bentonite over the entire wetting path, while the traditional approach overestimates the hydraulic conductivity without consideration of the microstructure effect.

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31

Liu, Ching-Yi, Yun-Da Hsieh, and Yung-Chia Chiu. "Simplified power law relationship in the estimation of hydraulic conductivity of unsaturated sands using electrical conductivity." Soil Research 59, no. 4 (2021): 406. http://dx.doi.org/10.1071/sr20190.

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The unsaturated zone is a complex multiphase system, and modelling and prediction of flow and contaminant transport in this zone remain a challenge. In order to understand the mechanisms of fluid flow in unsaturated sands, an accurate and efficient approach to estimate unsaturated hydraulic conductivity (K) is essential. In this study, a power law relationship was derived from a combination of Archie’s law and van Genuchten’s model to relate bulk (apparent) electrical conductivity (ECa) with unsaturated K. The laboratory sandbox experiments were conducted first to delineate the soil water characteristic curves (SWCCs). Time domain reflectometry was used to simultaneously measure volumetric water content (θ) and ECa. Then, the experimental relationships of the effective saturation (S) and ECa and simulated S–K were combined to establish the relationship between ECa and unsaturated K. The developed power law relationships described the relative EC (ECr) and relative K (Kr) very well by just using one parameter, exponent β. When fluid EC was low, the β values for the drainage and wetting processes ranged within 2.09–2.74 and 2.50–3.79 respectively. The variations of β values of homogeneous material were smaller that of heterogeneous material and the effect of hysteresis on the ECr–Kr relationship was observed. When pore space was filled with the high-EC solution, it easily mimicked the S–Kr relationship and resulted in a smaller β value. The β value acted as a lumped factor accounting for pore tortuosity, pore connectivity, shape of pore space, and fluid EC. The power law relationship of ECr–Kr developed in this study could lead to a direct estimation of the spatial and temporal variations of unsaturated K, once the measurements of SWCC are available from estimation of saturated K and combination of time-lapse ECa measurements. Accurate and efficient estimation of unsaturated K could improve the prediction of flow in the unsaturated zone and allow a comprehensive understanding of unsaturated zone processes.

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32

Jayawardane, NS. "Prediction of unsaturated hydraulic conductivity changes of a loamy soil in different salt solutions by using the equivalent salt solutions concept." Soil Research 30, no. 5 (1992): 565. http://dx.doi.org/10.1071/sr9920565.

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Equivalent salt solutions series have been previously defined as solutions with combinations of sodium absorption ratio (SAR) and electrolyte concentration (E,) producing the same extent of clay swelling in a given soil. These equivalent salt solutions series values have yielded satisfactory predictions of changes in saturated hydraulic conductivity, with changes in salt solution composition and concentrations. In the present study, previously published data on changes in saturated and unsaturated hydraulic conductivities of Gilat soil in salt solutions of cationic ratio 0-50 (mmol dm-3)1/2 and electrolyte concentration 2-50 (m.e. dm-3) were used to compare the equivalent salt solution series values for hydraulic conductivities at different water contents. The equivalent salt solution series causing a given change in saturated hydraulic conductivity of a loamy Gilat soil were derived. These equivalent salt solution values were used to predict the unsaturated hydraulic conductivities of this soil at low water contents. Predictions of unsaturated conductivity at relative water contents (�) ranging from 0.80 to 0.20 agreed closely with the measured values. Coefficients log a1 and b1 for Gilat soil, in the equation log Ec = log a1+b1 log SAR, relating the Ec and SAR values of each equivalent salt solutions series were determined at � values between 1.00 and 0.20. The relationship between log a1 and bl was similar at all water contents, in agreement with the equivalent salt solutions concept. Therefore, equivalent salt solution parameters derived from saturated hydraulic conductivity measurements could be used to predict changes in unsaturated conductivities and hence flow rates of saline water under specified boundary conditions.

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Zumr, David, Jakub Jeřábek, Vladimír Klípa, Michal Dohnal, and Michal Sněhota. "Estimates of Tillage and Rainfall Effects on Unsaturated Hydraulic Conductivity in a Small Central European Agricultural Catchment." Water 11, no. 4 (April 10, 2019): 740. http://dx.doi.org/10.3390/w11040740.

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In arable land, topsoil is exposed to structural changes during each growing season due to agricultural management, climate, the kinetic energy of rainfall, crop and root growth. The shape, size, and spatial distributions of soil aggregates are considerably altered during the season and thus affect water infiltration and the soil moisture regime. Agricultural topsoils are prone to soil compaction and surface sealing which result in soil structure degradation and disconnection of preferential pathways. To study topsoil infiltration properties over time, near-saturated hydraulic conductivity of topsoil was repeatedly assessed in a catchment in central Bohemia (Czech Republic) during three consecutive growing seasons, using a recently developed automated tension minidisk infiltrometer (MultiDisk). Seasonal variability of soil bulk density and saturated water content was observed as topsoil consolidated between seedbed preparations. Topsoil unsaturated hydraulic conductivity was lower in spring and increased in the summer months during two seasons, and the opposite trend was observed during one season. Temporal unsaturated hydraulic conductivity variability was higher than spatial variability. Cumulative kinetic energy of rainfall, causing a seasonal decrease in soil macroporosity and unsaturated hydraulic conductivity, was not a statistically significant predictor.

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Dong, Shaoyang, Yuan Guo, and Xiong (Bill) Yu. "Method for Quick Prediction of Hydraulic Conductivity and Soil-Water Retention of Unsaturated Soils." Transportation Research Record: Journal of the Transportation Research Board 2672, no. 52 (September 28, 2018): 108–17. http://dx.doi.org/10.1177/0361198118798486.

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Hydraulic conductivity and soil-water retention are two critical soil properties describing the fluid flow in unsaturated soils. Existing experimental procedures tend to be time consuming and labor intensive. This paper describes a heuristic approach that combines a limited number of experimental measurements with a computational model with random finite element to significantly accelerate the process. A microstructure-based model is established to describe unsaturated soils with distribution of phases based on their respective volumetric contents. The model is converted into a finite element model, in which the intrinsic hydraulic properties of each phase (soil particle, water, and air) are applied based on the microscopic structures. The bulk hydraulic properties are then determined based on discharge rate using Darcy’s law. The intrinsic permeability of each phase of soil is first calibrated from soil measured under dry and saturated conditions, which is then used to predict the hydraulic conductivities at different extents of saturation. The results match the experimental data closely. Mualem’s equation is applied to fit the pore size parameter based on the hydraulic conductivity. From these, the soil-water characteristic curve is predicted from van Genuchten’s equation. The simulation results are compared with the experimental results from documented studies, and excellent agreements were observed. Overall, this study provides a new modeling-based approach to predict the hydraulic conductivity function and soil-water characteristic curve of unsaturated soils based on measurement at complete dry or completely saturated conditions. An efficient way to measure these critical unsaturated soil properties will be of benefit in introducing unsaturated soil mechanics into engineering practice.

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Ahuja, L. R., J. D. Ross, R. R. Bruce, and D. K. Cassel. "Determining Unsaturated Hydraulic Conductivity from Tensiometric Data Alone." Soil Science Society of America Journal 52, no. 1 (January 1988): 27–34. http://dx.doi.org/10.2136/sssaj1988.03615995005200010005x.

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Ankeny, Mark D., Mushtaque Ahmed, Thomas C. Kaspar, and Robert Horton. "Simple Field Method for Determining Unsaturated Hydraulic Conductivity." Soil Science Society of America Journal 55, no. 2 (1991): 467. http://dx.doi.org/10.2136/sssaj1991.03615995005500020028x.

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Zhu, Jianting, and A. W. Warrick. "Unsaturated Hydraulic Conductivity of Repeatedly Layered Soil Structures." Soil Science Society of America Journal 76, no. 1 (January 2012): 28–35. http://dx.doi.org/10.2136/sssaj2011.0028.

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van den Berg, E. H., E. Perfect, C. Tu, P. S. K. Knappett, T. P. Leao, and R. W. Donat. "Unsaturated Hydraulic Conductivity Measurements with Centrifuges: A Review." Vadose Zone Journal 8, no. 3 (August 2009): 531–47. http://dx.doi.org/10.2136/vzj2008.0119.

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Ünlü, K., M. L. Kavvas, and D. R. Nielsen. "Stochastic analysis of field measured unsaturated hydraulic conductivity." Water Resources Research 25, no. 12 (December 1989): 2511–19. http://dx.doi.org/10.1029/wr025i012p02511.

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40

Meerdink, J. S., C. H. Benson, and M. V. Khire. "Unsaturated Hydraulic Conductivity of Two Compacted Barrier Soils." Journal of Geotechnical Engineering 122, no. 7 (July 1996): 565–76. http://dx.doi.org/10.1061/(asce)0733-9410(1996)122:7(565).

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41

Z. Samani and A. Blair. "A Simple Method for Measuring Unsaturated Hydraulic Conductivity." Applied Engineering in Agriculture 6, no. 3 (1990): 285–88. http://dx.doi.org/10.13031/2013.26383.

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42

NAKANO, M., Y. AMEMIYA, and K. FUJII. "SATURATED AND UNSATURATED HYDRAULIC CONDUCTIVITY OF SWELLING CLAYS." Soil Science 141, no. 1 (January 1986): 1–6. http://dx.doi.org/10.1097/00010694-198601000-00001.

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KABLAN, RICHARD A. T., R. S. MANSELL, S. A. BLOOM, and L. C. HAMMOND. "DETERMINATIONS OF UNSATURATED HYDRAULIC CONDUCTIVITY FOR CANDLER SAND." Soil Science 148, no. 3 (September 1989): 155–64. http://dx.doi.org/10.1097/00010694-198909000-00001.

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Chiu, Te-Fu, and Charles D. Shackelford. "Unsaturated Hydraulic Conductivity of Compacted Sand-Kaolin Mixtures." Journal of Geotechnical and Geoenvironmental Engineering 124, no. 2 (February 1998): 160–70. http://dx.doi.org/10.1061/(asce)1090-0241(1998)124:2(160).

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Bagarello, V., M. Castellini, and M. Iovino. "Comparison of unconfined and confined unsaturated hydraulic conductivity." Geoderma 137, no. 3-4 (January 2007): 394–400. http://dx.doi.org/10.1016/j.geoderma.2006.08.031.

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Ghanbarian-Alavijeh, Behzad, and Allen G. Hunt. "Unsaturated hydraulic conductivity in porous media: Percolation theory." Geoderma 187-188 (October 2012): 77–84. http://dx.doi.org/10.1016/j.geoderma.2012.04.007.

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47

Zayani, K., G. Vachaud, and N. Ennabli. "Estimation of unsaturated hydraulic conductivity from inflow data." Journal of Hydrology 138, no. 3-4 (October 1992): 503–14. http://dx.doi.org/10.1016/0022-1694(92)90133-g.

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Karim, Md Rajibul, David Hughes, and Md Mizanur Rahman. "Unsaturated Hydraulic Conductivity Estimation—A Case Study Modelling the Soil-Atmospheric Boundary Interaction." Processes 10, no. 7 (July 1, 2022): 1306. http://dx.doi.org/10.3390/pr10071306.

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Pore water pressure changes due to soil-atmospheric boundary interaction can significantly influence soil behaviour and can negatively affect the safety and stability of geotechnical structures. For example, prolonged rainfall events can lead to increased pore water pressure and lower strength; repeated cycles of pore water pressure changes can lead to degradation of strength. These effects are likely to become more severe in the future due to climate change in many parts of the world. To analyse the behaviour of soil subjected to atmospheric boundary interactions, several parameters are needed, and hydraulic conductivity is one of the more important and is difficult to determine. Hydraulic conductivity deduced from laboratory tests are often different from those from the field tests, sometimes by orders of magnitude. The problem becomes even more complicated when the soil state is unsaturated, where the hydraulic conductivity varies with the soil’s state of saturation. In this paper, a relatively simple alternative approach is presented for the estimation of the hydraulic conductivity of unsaturated soils. The method involved a systematic re-analysis of observed pore water pressure response in the field. Using a finite element software, the soil-atmospheric boundary interaction and related saturated/unsaturated seepage of an instrumented slope have been analysed, and results are compared with field measurements. The numerical model could capture the development of suction, positive pore water pressure and changes in water content with reasonable accuracy and demonstrated the usefulness of the hydraulic conductivity estimation method discussed in this paper.

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Zhu, J., and D. Sun. "Capillary pressure-dependent anisotropy of layered unsaturated soils." Canadian Journal of Soil Science 90, no. 2 (May 1, 2010): 319–29. http://dx.doi.org/10.4141/cjss09047.

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This paper presents an approach based on a conceptualization of combining the neural network based pedo-transfer function (PTF) results with the thin layer concept to explore capillary-pressure-dependent anisotropy in relation to soil texture and soil bulk density. The effects of capillary pressure (or saturation degree) on the hydraulic conductivity anisotropy of unsaturated soils are still poorly understood. The main objective is to examine how anisotropy characteristics are related to the relationships between hydraulic parameters and the basic soil attributes such as texture and bulk density. The hydraulic parameters are correlated with the texture and bulk density based on the pedo-transfer function (PTF) results. It is demonstrated that non-monotonic behavior of the unsaturated soil anisotropy in relation to the capillary pressure is only observed when the saturated hydraulic conductivity and the shape parameter are both related to the particle diameter. Therefore, it is suggested that this behavior is mainly due to the coupled dependence of the layer saturated hydraulic conductivities and the shape factors on the texture and bulk density. The results illustrate that the inter-relationships of soil texture, bulk density, and hydraulic properties may produce vastly different characteristics of anisotropic unsaturated soils.Key words: Anisotropy, unsaturated soils, capillary pressure-dependent

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Rezanezhad, F., W. L. Quinton, J. S. Price, D. Elrick, T. R. Elliot, and R. J. Heck. "Examining the effect of pore size distribution and shape on flow through unsaturated peat using computed tomography." Hydrology and Earth System Sciences 13, no. 10 (October 28, 2009): 1993–2002. http://dx.doi.org/10.5194/hess-13-1993-2009.

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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.

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