• Journal of the Korean GEO-environmental Society
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• v.12 no.2
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• pp.23-33
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• 2011

In this paper, we got soil-water characteristic curve(SWCC) of Nak-Dong River's sand respectively as relative density 40%, 60%, 80% and content of silt 0%, 10%, 20%, 30%. As a result, the more the sand densify in the same silt content and the more the sand has silt in the same relative density, the change of volume water content was decreased. we have known effect of silt contents for SWCC and verified existing empirical formula of SWCC. As experiment results of soil-water characteristic curves compared to the empirical solutions, the results of van Genuchten(1980) and Fredlund & Xing(1994) were well-matched showing S type curves with experiment results. Especially the empirical solution of Fredlund & Xing showed almost same results of the coefficient of correlation($R^2$) equal to 0.99.

• Journal of Industrial Technology
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• v.29 no.A
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• pp.145-153
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• 2009

In this study, to determine characteristics of compaction and the soil water characteristic curve(SWCC) in decomposed granitic soils, compaction tests and SWCC tests were carried out for samples having various contents of coefficient of uniform($c_u$), By compacting their samples with standard Proctor density test, the effects of binder contents on maximum dry density and optimum moisture content were investigated and compared. Samples compacted with the maximum dry density and the optimum moisture content were tested by means of the SWCC, to determine their SWCC parameters, such as Brooks & Corey(${\lambda}$, ${\Psi}_b$), Van Genuchten (${\alpha}$, n, m), Fredlund & Xing(a, n, m).

• Journal of the Korean Geotechnical Society
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• v.28 no.4
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• pp.91-100
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• 2012

Soil-water characteristic curves (SWCCs), which represent a physical property in partially saturated soils, show the relation between volumetric water content and matric suction. The SWCCs exhibit hysteresis during wetting and drying, however experimental expressions used to describe SWCCs have generally ignored the hysteresis. In addition, the shape of SWCC may depend on the void ratio which is changed by soil skeleton deformations or hysteretic behavior under various loading conditions. Hence, it is necessary to understand, both empirically and analytically, the relationship between soil skeleton deformations and the SWCCs of various soils. The typical SWCCs experimentally have drying, wetting, and the second drying curve. The measurement of a complete set of hysteretic curves is severely time-consuming and difficult works, then the first drying curve of SWCC is generally determined to estimate the hydraulic conductivity and shear strength function of partially saturated soils. This paper presents the hydraulic-mechanical behavior of partially saturated soils (weathered soil and silty soil) for volume changes and hysteresis in SWCCs regarding the difference between the first drying and wetting curve.

• Journal of the Korean Geotechnical Society
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• v.19 no.4
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• pp.15-21
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• 2003

A series of triaxial compression tests were performed on samples of compacted granite soil in a modified triaxial cell that allowed separate control of pore air pressure ($U_a$) and pore water pressure ($U_w$) in order to examine the characteristics of pore pressure, volume change and stress-strain behavior during undrained loading conditions. Triaxial samples of unsaturated and saturated compacted granite soil, 50mm in diameter and 100mm in height, were prepared by compaction in a mould. These samples were tested at 3 different suction values (0.5, 1.0, 2.0 kgf/cm$^2$) for unsaturated compacted granite soil and at 3 different confining stresses (1.0, 2.0, 4.0 kgf/cm$^2$). Results showed that only effective cohesion increased with little variation of friction angle, according to matric suction.

• Journal of the Korean Geotechnical Society
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• v.40 no.3
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• pp.7-18
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• 2024

In this study, slope stability was evaluated in consideration of unsaturated soil behavior to predict landslides. Samples were collected from a landslide site due to heavy rainfall during Typhoon Hinnamnoh. Soil moisture characteristic tests were performed based on the evaporation method using a swelling undisturbed sample and a remolded sample. Based on the hydraulic-mechanical behavior, two-dimensional infiltration and stability analyses were performed. As a result, from the two sample types, it is found that both behaviors exhibited clear differences in the results, and the behavior of the swelling undisturbed sample was able to predict the actual slope failure appropriately.

• Journal of the Korean Geotechnical Society
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• v.40 no.1
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• pp.47-54
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• 2024

In current slope stability analysis techniques, slope stability is evaluated based on the saturated-soil theory. However, soil-water characteristics change frequently depending on the climate. Therefore, because the saturated soil theory has limitations, the application of the unsaturated soil theory is necessary for slope stability. It is also important to evaluate the engineering properties of unsaturated soil because the capillary absorption capacity is reduced due to heavy rain, thereby causing a reduction in slope stability. In this study, soil-water characteristic tests were performed using four samples with different fine contents (0%, 10%, 20%, and 30%) using granite-weathered soil in domestic production areas. In particular, to consider the previously conducted drying process as well as the evaluation of stability due to heavy rain on the actual slope, a wetting process was conducted, in which the water content was increased. In addition, the van Genuchten (1980) model, which is the most consistent theoretical equation for the experiment, was used with various theoretical equations, and the parameters were analyzed according to the fine content of the granite-weathered soil for the drying and wetting processes.

• Korean Journal of Soil Science and Fertilizer
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• v.39 no.5
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• pp.259-267
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• 2006

Hydraulic conductivity is the rate of water flux on hydraulic gradient. The van Genuchten Mualem (VGM) model is frequently used for describing unsaturated state of soils, that is composed with the function of soil water potential and soil water content and requests various parameters. This study is to get the value of VGM parameters used Rosetta computer program based on neural network analysis method and to calculate VGM parameters. VGM parameters included Ko(effective saturated hydraulic conductivity), ${\theta}r$(residual soil water content), ${\theta}s$(saturated soil water content), L, n and m. The unsaturated hydraulic conductivity at 10 kPa was calculated by using Rosetta program. Unsaturated hydraulic conductivities of 17 soil series at 1, 3, 5, 7 kPa were also obtained by applying saturated hydraulic conductivity by disk tension infiltrometer based on Gardner and Wooding's equation. Water flow at the water potential of 3 kPa was very low except Namgye, Hagog, Baegsan, Sangju, Seogcheon, Yesan soil series. Unsaturated hydraulic conductivity at 1 kPa showed the highest value for Samgag soil series and was in order of Yesan, Hwabong, Hagog and Baegsan soil series. Those of Gacheon, Seocheon and Ugog soil series were very low. When the value by VGM was compared with the value by disc tension infiltrometer, there was a tendency with exponential function to soils without gravel but there was no tendency to soils including gravel. Conclusively, it would be limited that VGM model for unsaturated hydraulic conductivity analysis applies to Korean agricultural land including gravel and having steep slope, shallow soil depth.

• Korean Journal of Soil Science and Fertilizer
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• v.36 no.4
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• pp.181-192
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• 2003

We developed a mathematical simulation model to portray the vertical distribution of soil water from the measured weather data and the known soil hydraulic properties, and then compared simulation results with the periodically measured soil water profiles obtained on Jungdong sandy loam to verify the model, In this model, we solved potential-based Richards' equation by the implicit finite difference method superimposed on the predictor-corrector scheme. We presumed that: soil hydraulic properties are homogeneous; soil water flows isothermally; hysteresis is not considered; no vapor flows; no heat transfers into the soil profiles; and water added to soil surface is distributed along the soil profile following partial displacement principle. The input data were broadly classified into two groups: (1) daily weather data such as rainfall, maximum and minimum air temperatures, relative humidity and solar radiation and (2) soil hydraulic data to approximate unsaturated hydraulic conductivity and water retention. Each hydraulic polynomial function approximated using the Chebyshev polynomial and least square difference technique in tandem showed a fairly good fit of the given set of data. Vertical distribution of soil water as approximations to the Richards' equation subject to changing surface and phreatic boundaries was solved numerically during 53 days with a comparatively large time increment, and this pattern agreed well with field neutron scattering data, except for the surface 0.1 m slab.

• Journal of the Korean Geotechnical Society
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• v.39 no.5
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• pp.13-26
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• 2023

This study examined the soil-water characteristic curve (SWCC), considering the volume change, using wetting curves on the field monitoring data of a wireless sensor network. Special attention was given to evaluating the landslide vulnerability by deriving a matric suction suitable for the actual site during the wetting process. Laboratory drying SWCC and shrinkage laboratory tests were used to perform the combined analysis of landslide and debris flow. The results showed that the safety factor of the wetting curve, considering the volume change of soil, was lower than that of the drying curve. As a result of numerical analyses of the debris flow simulation, more debris flow occurred in the wetting curve than in the drying curve. It was also found that the landslide analysis with the drying curve tends to overestimate the actual safety factor with the in situ wetting curve. Finally, it is confirmed that calculating the matric suction through SWCC considering the volume change is more appropriate and reasonable for the field landslide analysis.

• Journal of the Korean GEO-environmental Society
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• v.24 no.10
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• pp.15-23
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• 2023

In this study, the infiltration behavior of slopes composed of mixed soils with clay contents of 0%, 5%, and 10% in weathered Gneiss soil, which is a representative weathered soil in Korea, was investigated, and the stability of unsaturated slopes due to rainfall infiltration was examined. For this, in this study, the soil water characteristic curve was obtained through the water retention test, and the strength constant was obtained through the triaxial compression test. Based on the obtained results, the influence of clay content and antecedent rainfall effect (i.e., initial suction) on the formation of saturated zone (i.e., wetting band) and slope stability due to rainfall infiltration was examined through infiltration and stability analyses. As a result, it was found that the hig her the initial suction, the slower the formation of the saturated zone on the slope. In addition, it was found that as the clay content increases, the shear strength of the ground increases and the resistance to rainfall infiltration increases, and eventually the slope stability is greatly improved.