• Journal of the Korean Geotechnical Society
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• v.20 no.3
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• pp.47-51
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• 2004

An unsaturated hydraulic conductivity function and a soil-water characteristic curve are the essential constitutive factors in studying unsaturated soils. In order to obtain the unsaturated hydraulic conductivity function, prediction functions, which are based on the soil-water characteristic curve, have been used because it is difficult to measure the unsaturated hydraulic conductivity function directly. In this study, a parameter estimation method using the flow pump technique is introduced to determine the unsaturated hydraulic conductivity function. This method provides more accurate and independent solution than previous methods for the determination of the unsaturated hydraulic conductivity function which is not subordinate to the soil-water characteristic curve or prediction models.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.6
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• pp.2369-2379
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• 2013

The Soil-Water Characteristics Curve (SWCC) is affected by the initial density of soil under unsaturated condition. Also, the characteristic of hydraulic conductivity is changed by the initial density of soil. To study the effect of initial density of unsaturated soil, SWCC and the Hydraulic Conductivity Function (HCF) of Jumoonjin sand with various relative densities, 40%, 60% and 75% were measured in both drying and wetting processes. As the results of SWCC estimated by van Genuchten (1980) model, the parameter related to Air Entry Value(AEV), ${\alpha}$ in the wetting process is larger than that in drying process, but the parameters related to the SWCC slope, n and the residual water content, m are larger than those in wetting process. The AEV is increased or Water Entry Value (WEV) is decreased with increasing the relative density of sand. The AEV is larger than the WEV at the same relative density of sand. As the results of HCF estimated by van Genuchten (1980) model which is one of the parameter estimation methods, the unsaturated hydraulic conductivity maintained at a saturated one in the low level of matric suctions and then suddenly decreased just before the AEV or the WEV. The saturated hydraulic conductivity in drying process is larger than that in wetting process. The saturated hydraulic conductivity is decreased with increasing the relative density of sand in both drying and wetting processes. Also, the hysteresis in unsaturated HCFs between drying and wetting process was occurred like the hysteresis in SWCCs. According to the test results, the AEV on SWCC is decreased and the saturated hydraulic conductivity is increased with increasing the initial density. It means that SWCC and HCF are affected by the initial density in the unsaturated soil.

• Journal of the Korean Geotechnical Society
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• v.21 no.5
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• pp.59-64
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• 2005

In studying unsaturated soil mechanics, determination of soil water characteristic curve and permeability equation though not easy, is an essential factor. In this research a new testing apparatus was developed to determine soil water characteristic curve and permeability equation. A test to get saturated permeability coefficients and soil water characteristic curves for two soils was performed by using the developed testing apparatus. First, a saturated permeability test was performed and then the test to get soil water characteristic curve of a drying process was performed. Next, the test to get soil water characteristic curve of a wetting process was performed. Test results showed hysteresis phenomena between soil water characteristic curve of a drying process and soil water characteristic curve of a wetting process. The permeability equations were determined by a theoretical method where a saturated permeability coefficient and a soil water characteristic curve were used.

• Journal of the Korean Geotechnical Society
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• v.26 no.10
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• pp.49-60
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• 2010

Unsaturated permeability function is an important factor in the design and analysis of various unsaturated soil structures. Generally the permeability characteristics decrease as the mat ric suction increases and the trend is similar to water retention characteristics of a soil. The permeability of unsaturated soils can be obtained directly by laboratory tests or indirectly by estimation methods from other soil properties. For unsaturated soils sampled from 7 areas in KOREA, SWCCs and unsaturated permeability functions were obtained by experimental tests. The unsaturated permeability results were also compared with the unsaturated permeability functions derived from the SWCCs theoretically. However, the current estimation models of unsaturated permeability function did not express the unsaturated permeability characteristics. Therefore, the FXK-M permeability function was modified to predict more accurate permeability functions for Korean weathered soils using a correction factor that can be calculated from the air-entry value of SWCC. The new estimation model resulted in good agreements for all tested soils.

• The Journal of Engineering Geology
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• v.28 no.1
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• pp.25-34
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• 2018

The physical properties and unsaturated characteristics of acid sulfate soils were investigated and analyzed. As the results of measuring physical properties of the acid sulfate soils obtained around the Ilkwang mine area, the dry unit weight is $1.246t/m^3$ and this soil is classified into the silty sand (SM) by USCS. Soil Water Characteristics Curves (SWCC) of the drying and wetting paths were measured by the automated SWCC apparatus. Also, Hydraulic Conductivity Functions (HCF) of the drying and wetting paths were estimated by the van Geunchten (1980) model which is the most well-known parameter estimation method. The hydraulic conductivity of acid sulfate soils in the dry path was continuously decreased with increasing the matric suction. However, the hydraulic conductivity in the wetting path was decreased relatively small with increasing matric suction and decreased suddenly just before water entry value of matric suction. Meanwhile, the hysteresis phenomenon was occurred in SWCCs and HCFs during the drying and wetting paths.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.32 no.1C
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• pp.7-16
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• 2012

In this paper, using the principle of Static Measurement Methods suggested by Huang (1998), a new experimental device has been made and used in order to calculate the unsaturated permeability of Nak-dong river sand with silt which is an important basic property in the unsaturated soil. This device was designed to measure changes of the unsaturated permeability according to the increase of matric suction. The value of the unsaturated permeability obtained in testing and that obtained using the empirical permeability functional formula were compared and analyzed. As a result, the value of the unsaturated permeability tends to be decreased according to the increase of relative density, silt content and matric suction. This tendency shows it is very closely related to the change of moisture content and void ratio. The empirical permeability functional formula presented by Frelund & Xing (1995) was regarded as the most appropriate model to represent the unsaturated permeability of Nak-dong River silty sand.

• Journal of Korea Water Resources Association
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• v.33 no.1
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• pp.133-142
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• 2000

Series of tests were carried out to study permeability characteristics of unsaturated soils. The weathered soils taken from Inju, Sungwhan, and Kuri, were selected to have different amount of fine grained soils in order to find a possible correlation between the unsaturated permeability behavior and fine grained soils contents. Measurements of permeability for unsaturated soils were performed with a newly developed apparatus, which modeled after Klute's apparatus(1965a). The apparatus was designed to measure volumetric water content and permeability by applying incremental suction pressure. Permeability and volumetric water content of unsaturated soils generally decreased as density of the soil increased. The relationship between volumetric water content and permeability was not related to the fine grained soils contents because the plots scattered widely. By comparing volumetric water content with permeability, empirical parameters A and B could be determined, which made to be possible to predict unsaturated permeability from soil-moisture characteristics.

• Journal of the Korean GEO-environmental Society
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• v.10 no.7
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• pp.143-150
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• 2009

Material functions about effective stress, permeability, coefficient of consolidation and coefficient of volume change has important role to predict consolidation velocity and settlement of soft ground. Modified oedometer for radial drainage is adapted to find out material functions on laboratory tests. Undisturbed sample for laboratory tests were taken from construction sites of industrial complexes on southern coastal area which consists of upper dredged fill and lower original clay layer. For different drainage condition in consolidation process void ratio, effective stress, permeability, coefficient of consolidation and coefficient of volume change has been assessed with results of existing standard oedometer tests. It is worthwhile to note that consolidation material functions could be expressed as regression equation by Stark (2005), heterogeneity for permeability could be assessed from these relationships.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.13 no.5
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• pp.261-273
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• 1993

In order to study hydraulic properties and mechanical properties on unsaturated region, soil-water retention curve was obtained for suction plate method and pressure plate method, respectively. To investigate permeability of unsaturated soil and soil-water retention curve at the same time, unsaturated permeability tests using an improved Richard's method were performed on Joomoonjin Sand. These experimental results were compared with those by empirical equations. The relationship between air entry value and saturated permeability of filter was obtained for selecting a proper filter in unsaturated soil tests.

• Water for future
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• v.27 no.3
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• pp.107-113
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• 1994

The analysis of Richards eq. requires data of the soil water retention function and the unsaturated hydraulic conductivity. The soil water retention function was measured through the use of the developed apparatus and the saturated hydraulic conductivity was measured by the constant head method for each soil sample corresponding to the A, B, C types of SCS. In order to obtain one water retention function and one unsaturated hydraulic conductivity which represent each soil group, van Genuchten's eq. and Mualem's pore-structure model was chosen respectively. Parameters of van Genuchten's eq. are estimated for each soil group using data obtained in the experiments, and estimated values give a basis to analyze the unsaturated flow in the non-measured region efficiently.