• Geomechanics and Engineering
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• v.36 no.4
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• pp.343-353
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• 2024

The hydraulic anisotropic behavior of unsaturated soil has not been fully explored in relation to the grain-size distribution. The present study conducted laboratory assessments to examine the hydraulic anisotropy condition of statically compacted specimens in various initial states. The investigation incorporated the concept of hydraulic anisotropy by employing two discrete forms of soil stratification: horizontal-layering (HL) and vertical-layering (VL). The examined soils comprised sandy silt and silty sand, exhibiting either unimodal or bimodal soil-water characteristic curve (SWCC). This study aimed to investigate the potential correlation between the hydraulic anisotropy ratio and soil properties. The present study established a correlation between the hydraulic anisotropy ratio and several soil parameters, including fine content, dry density, plastic limit, and liquid limit. The study results indicate a non-linear relationship between the percentage of fine and dry density in soils with unimodal and bimodal soil-water characteristic curve (SWCC) and hydraulic anisotropy ratio.

• 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.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.33 no.3
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• pp.1017-1025
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• 2013

The monolithically coupled finite element analysis for a deformable unsaturated soil slope is performed to investigate matric suction distribution on a soil slope subjected to rainfall infiltration, which can consider the hydraulic-mechanical characteristics for the analysis. The soil-water characteristic curves (SWCC) are experimentally determined to estimate three types of hydraulic properties of domestic areas. Based on the physical properties, the distribution of matric suction is investigated by considering the major factors, such as soil conditions, rainfall intensities, and slope angles. It is found from the results of this study that the matric suction rapidly decreases with an increase in rainfall intensity, regardless a slope angle. The slope surface is more easily saturated when its saturated hydraulic conductivity is smaller than rainfall intensity, and for the case of multi-layered soil slope, hydraulic characteristics of slope surface has a significant influence on matric suction distribution.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.31 no.1D
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• pp.83-90
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• 2011

A need still exists that the unsaturated condition is to be considered when evaluating the infiltration and drainage capacity for compacted geomaterials in road foundation or embankments. For this reason, numerical analysis were used to analyze the time-dependent unsaturated infiltration and drainage condition depending on various geomaterial types. Therefore, laboratory data from the soil-water characteristic curve tests on geomaterials were adopted from previous studies. In addition, the unsaturated permeability was estimated using SWCC. Then the infiltration and drainage performance of unsaturated compacted soils were evaluated under various conditions based on the proposed method. The results demonstrated that the effect of initial suction and SWCC path on each material could be substantial and the proper application on analysis is very important to enhance the prediction on each capacity.

• 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.

• Journal of the Korean Geotechnical Society
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• v.28 no.9
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• pp.23-30
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• 2012

This paper is research results of slope stability analysis associated with seepage infiltration for unsaturated soil in debris-flow occurrence slopes. Site investigations were carried out in two slopes, located at Inje in Kangwon province where debris flow occurred in 2006 and at Yangpyung in Kyeunggi province where it occurred in 2010. For unsaturated soil sampled at the zone of debris-flow initiation, soil water characteristic curves with tempe pressure cells and shear strength parameters with newly designed shear strength apparatus were obtained respectively. The commertially available software SEEP/W was used to analyze seepage infiltration in unsaturated soil, based on their properties obtained from test results and the actual rainfall data at the moment of debris flow occurrence, and slope stability analysis with the program of SLOPE/W, associated with results of seepage analysis, was performed to simulate slope failure. As results of this research, seepage infiltration to unsaturated soil due to intensive rainfall was found to cause increase of ground water table as well as degree of saturation. Through this research slope stability analysis for unsaturated soil, considering the actual rainfall characteristic, might be a reasonable method of investigating characteristics of debris flow behavior, in particular, the moment of debris flow occurrence.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.699-708
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• 1997

The effective unsaturated hydraulic conductivity in stratified soils is evaluated using a three-dimensional stochastic approach. Because of the disparity of the correlation scales in a stratified soil, the general stochastic equations are simplified. This allows analytical evaluation of generic expressions for the effective hydraulic conductivities. Simple asymptotic expressions, valid at particular ranges(wetting front, drying condition, wetting condition) of the mean flow characteristics, are also derived. An example of applying the derived theoretical result to a imaginaryl clay soil is presented. It reveals found that the effective unsaturated hydraulic conductivity showed large-scale hysteresis. Such large-scale hysteresis was produced by the spatial variability of hydraulic soil properties rather than hysteresis of the local parameters. In addition the results show that the effective hydraulic conductivities were larger in the case of accommodating heterogeneity of soil preperties rather than neglecting heterogeneity of soil properties.

• Journal of the Korean Geotechnical Society
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• v.18 no.6
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• pp.83-101
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• 2002

Elastic waves provide an important information about the soil mass in the near-surface. Soil properties in relation to elastic wave parameters are clarified to facilitate the application of geophysical technique to soil characterization. As an example, experiments are performed to gain further insight into the behavior of unsaturated particulate materials using bender elements. The small strain stiffness is continuously measured on specimens subjected to drying, and changes in stiffness are related to changes in interparticle forces such as capillarity, bonding due to ion sharing, buttress effect due to fine migration, and cementation due to salt precipitation. The rate of menisci regeneration is studied after a perturbation as well. Finally, several phenomena associated with the evolution of capillary forces during drying are identified.

• Journal of the Korean Geotechnical Society
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• v.32 no.6
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• pp.27-40
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• 2016

Conventional warning criteria for landslides due to rainfall in broad regions have limitations, because they did not have proper reflection of topography, forest physiognomy, and unsaturated soil properties, et al. This study suggested a new stability model for unsaturated slope analyses during rainfall, considering rainfall pattern, geomorphological characteristics (slope angle, soil depth), engineering properties of unsaturated soils, and tree surcharge and root reinforcement. Stability analysis not considering root reinforcement and tree surcharge tends to over-predict a factor of safety in unsaturated slopes. Developed slope stability model was used to build database on the factor of safety in unsaturated slopes during rainfall, and it was integrated with GIS to do quantitative risk analysis in landslide risk areas specified in Ulju. Landslide risk areas were located at downstream of the point with sudden drop in safety factor, as well as at regions with low safety factor during rainfall.

• Geomechanics and Engineering
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• v.37 no.2
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• pp.109-122
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• 2024

Standard triaxial cells are commonly used to measure the mechanical behavior of saturated soils. However, this type of standard system is difficult to use for unsaturated soil specimens since it cannot measure the changes in the pore-air volume and pressure. This paper proposes to extend the measurement possibilities of the standard triaxial testing device in a simple way and to adapt it to partially saturated soils. The system is supplied by two hygrometers installed at each end of the cylindrical unsaturated specimen to measure local relative humidity, which allows the derivation of suction. The volumetric strain of the specimen is calculated by analyzing digital photos captured from the outside of the transparent cell wall. Specimens made of kaolin clay, having different hydraulic properties, were tested to verify the reliability of the measurements, and thus, the relevance of the proposed techniques to study the mechanical behavior of unsaturated soils.