• 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.

• Journal of The Korean Society of Agricultural Engineers
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• v.55 no.4
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• pp.1-11
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• 2013

Unsaturated hydraulic conductivity function is one of key parameters to solve the flow phenomena in problems of landslide. Prediction models for hydraulic conductivity function related to soil-water retention curve equations in many geotechnical applications have been still used instead of direct measurement of the hydraulic conductivity function since prediction models from soil-water retention curve equations are attractive for their fast and easy use and low cost. However, many researchers found that prediction models for the hydraulic conductivity function can not predict the hydraulic conductivity exactly in comparison with experimental outputs. This research introduced an inverse analysis to evaluate the hydraulic conductivity function corresponding to experimental output from the flow pump system. Optimisation process was carried out to obtain the hydraulic conductivity function. This research showed that the inverse analysis with flow pump system was suitable to assess the hydraulic conductivity in unsaturated soil, and the prediction models for the hydraulic conductivity were led to the significant discrepancy from actual experimental outputs.

• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2003.09a
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• pp.99-101
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• 2003

Unsaturated hydraulic conductivity models have been widely used for the numerical modeling of water flow and contaminant transport in soils. In this study, a simple hydraulic conductivity model is developed by using information of particle-size distribution from the lognormal distribution model and its results are compared with those from the Kosugi-Mualem (KM) model. The accuracy of the proposed model is verified for observed data chosen from the international UNSODA database. Results showed that the proposed model produces adequate predictions of hydraulic conductivities. Performance of this model is generally better than the KM function.

• 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.

• 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.

• Geomechanics and Engineering
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• v.22 no.2
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• pp.153-163
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• 2020

Laboratory experiments were conducted with two different soil conditions to investigate rainfall infiltration characteristics. The soil layer materials that were tested were weathered granite soil and weathered gneiss soil. Artificial rainfall of 80 mm/hr was reproduced through the use of a rainfall device, and the volumetric water content and matric suction were measured. In the case of the granite soil, the saturation velocity and the moving direction of the wetting front were fast and upward, respectively, whereas in the case of the weathered gneiss soil, the velocity and direction were slow and downward, respectively. Rainfall penetrated and saturated from the bottom to the top as the hydraulic conductivity of the granite soil was higher than the infiltration capacity of the artificial rainfall. In contrast, as the hydraulic conductivity of the gneiss soil was lower than the infiltration capacity of the rainfall, ponding occurred on the surface: part of the rainfall first infiltrated, with the remaining rainfall subsequently flowing out. The unsaturated hydraulic conductivity function of weathered soils was determined and analyzed with matric suction and the effective degree of saturation.

• Journal of the Korean Geotechnical Society
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• v.33 no.9
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• pp.5-22
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• 2017

The procedure that combines the result of infiltration analysis into stability analysis based on the limit equilibrium method is widely used to evaluate the impact of rainfall infiltration on slope stability. Accurate prediction of rainfall infiltration is essential to the prediction of landslides caused by rainfall, requires to obtain accurate unsaturated hydraulic properties of the soil. Among the unsaturated hydraulic characteristics of the soil, the importance of the soil-water characteristic curve describing the retained water characteristics of the soil is relatively well known and the measurement by test method to obtain the SWCC is gradually increasing. However, it takes a lot of time and expenses to experimentally measure the unsaturated conductivity characteristics of the soil. Therefore, it is common practice to estimate the hydraulic conductivity function from the SWCC. Although it is widely known that the SWCC has a great influence on rainfall infiltration, studies on the effect of the hydraulic conductivity function estimated from the SWCC on rainfall infiltration are very limited. In this study, we explained how the estimation model of the hydraulic conductivity function affects rainfall infiltration and slope stability analysis. To this end, one-dimensional infiltration analysis and slope stability analysis were conducted by using the data on the SWCC of weathered granite soil widely distributed in Korea. The applicability of each estimation model is discussed through review of the analysis results.

• Journal of The Korean Society of Agricultural Engineers
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• v.54 no.5
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• pp.129-139
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• 2012

Accurate modeling rainfall induced landslide and slope stability requires a detailed knowledge of the distribution of material strength characteristics and suction distribution. However, material properties obtained from the drying cycle are still used for infiltration analysis in many cases, even though material properties of wetting cycle are quite different from those of drying cycle due to hydraulic hysteresis and air occlusion. Therefore, the selection of proper material properties such as soil-water retention curve (SWRC) and the hydraulic conductivity function (HCF) reflecting characteristics of wetting cycle and air occlusion is an essential prerequisite in order to simulate the infiltration phenomena and to predict the suction and water content distribution in unsaturated soils. It is concluded that the simulation of infiltration with material properties from the drying cycle did not reasonably match with experimental outputs. Further discussion is made on how to describe the material properties considering air occlusion during wetting cycle over the entire suction range in order to simulate infiltration phenomena.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.300-305
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• 2003

One of the most important parts in constructing radioactive waste repository may be its safety aspect. The fundamental function of the repository is to isolate completely and forever the radioactive wastes disposed of in it. However, since either normally or abnormally nuclides are to be released from the repository with a certain causes. The hydraulic conductivity is related to transportation of nuclide in soil. However, hydraulic characteristics research in unsaturated soil is not enough at present time. A fast and easy procedure for estimating unsaturated flow parameters is presented. The estimation is based on direct measurement of the retention characteristics combined with inverse estimation of the hydraulic conductivity characteristics from one-step outflow experiment.

• Journal of the Korean Geotechnical Society
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• v.34 no.3
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• pp.5-12
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• 2018

Tests for transient water release and imbibitions measurement were conducted to estimate the unsaturated hydraulic conductivities by using back analysis. By using transient hydraulic characteristics, both the soil water retention curve and hydraulic conductivity fuction can be evaluated effectively and accurately. In this study the experiment for three samples were conducted accurately to measure the change of water content with time for various steps of matric suction. The back analysis calculated the amount of transient flow reliably in comparison with the experimental results. In the soil water retention curve there was no significant difference between the result of back analysis and that of experiment. The hydraulic conductivity function from back analysis was compared with the theoretical relation based on retention curve but they showed much difference. However, the unsaturated hydraulic behavior obtained by the combination of experimental and analytical techniques are considered to agree with the actual behavior.