• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.111-118
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• 2008

The purpose of this paper was to investigate the overburden effect on soil-water characteristic curve and unsaturated permeability of unsaturated weathered soils. For this, unsaturated suction and permeability tests under various overburden stress were conducted respectively. Then, the coefficient of unsaturated permeability and moisture capacity of weathered soils were estimated and compared. All these results are presented in the paper.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.28-33
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• 2006

Shallow failures of slopes in weathered soils are caused by infiltration due to prolonged rainfall. These failures are mainly triggered by the deepening of the wetting band accompanied by a decrease in suction induced by the water infiltration. In this paper, hysteresis on soil-water characteristic curve(SWCC) of granite and gneiss weathered soils are investigated using transient flow analysis respectively. Each case was subjected to artificial rainfall intensities and time duration depending on the laboratory-based drying and wetting processes. The results show that the unsaturated seepage on weathered slopes are very much affected by the initial suction of soils and unsaturated permeability of the soils. In addition, a granite weathered soil has a lower air-entry value, residual matric suction, and wetting front suction and less hysteresis loop than a gneiss weathered soil.

• Proceedings of the Korean Geotechical Society Conference
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• 2010.03a
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• pp.599-606
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• 2010

It has been reported that many slope failures in unsaturated soils are mainly caused by downward infiltration due to rainfall. The rainfall characteristics could be an important factor, and more predictable slope failures can be achieved by considering more reasonable rainfall conditions. So, a need exists that these trends of infiltration in weathered soils, which is commonly found in Korea, are assessed by considering rainfall conditions based on phenomenological approach. In this paper, numerical analyses of unsaturated soil slope under rainfall conditions are presented based on the soil-water characteristic curve in the laboratory and huff method. Then the performance of unsaturated weathered soil slopes was evaluated under various conditions after applying the effect of overburden pressure on SWCCs and fines contents. The results demonstrated that the rainfall conditions using Huff method can be very effective and the proper application on analysis is very important to enhance the prediction on unsaturated slope stability.

• Land and Housing Review
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• v.9 no.2
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• pp.51-57
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• 2018

The causes of landslides are dependant on rainfall events and the soil characteristics of a slope. For the conventional slope stability, the slope stability analysis has been carried out assuming the saturated soil theory. But, in order to clearly explain a proper soil slope condition by rainfall, the research should be performed using the unsaturated soil mechanism suitable for a soil slope in the field. In the study, by using two major categories of soils in Korea, such as granite and gneiss weathered soils, landslide model test and finite element method have been compared with the difference of seepage and soil stability analysis. The hydraulic conductivity of gneiss weathered soil is slower than that of granite weathered soil, and the gneiss weathered soil contains much finer soils than the granite weathered soil. It was confirmed that the instability of the slope was progressing slowly due to the slow rate of volumetric water content of the surface layer.

• 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.

• Journal of the Korean GEO-environmental Society
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• v.13 no.4
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• pp.45-51
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• 2012

The shear strength of weathered granite soils under unsaturated condition was evaluated by $K_0$ consolidated triaxial tests. Various matric suctions in the unsaturated triaxial tests were applied using suction-controlled triaxial test apparatus for weathered granite soils obtained in Daegu. Soil water characteristic curve (SWCC) laboratory tests for drying and wetting procedure were performed and van Genuchten curves were fitted by experimental results. The contribution of matric suction in unsaturated soils is directly correlated to effective stress and evaluated from SWCCs. The effective stresses were estimated from these SWCCs and the relationship between effective stress and unsaturated shear strength was determined. In the effective stress description, the unsaturated shear strength with respect to various suctions indicates unique relationship and almost the same as that of the saturated envelope.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.30 no.1C
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• pp.53-63
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• 2010

Since the water retention curve is considered as a major parameter to evaluate the unsaturated ground or soils, overburden pressure and clay content on soils underneath ground surface have not been considered for estimating water retention characteristics. Therefore, a need exists that the effect of overburden pressure and clay content on water retention characteristics was assessed in typical weathered soils found in Korea. Soil-Water Characteristic Curve and the unsaturated hydraulic conductivity were estimated using water retention characteristics under the condition of different overburden pressure, clay content, and de-saturation path. Then, these effects are evaluated with the results of SWCC tests from the laboratory. In addition to that, the unsaturated moisture capacity and diffusivity of each case is discussed.

• Proceedings of the Korean Geotechical Society Conference
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• 2004.03b
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• pp.334-341
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• 2004

The coefficient of permeability is one of the most important properties in unsaturated soils. The permeability varies with change in the water content as the soil water characteristic curve(SWCC) does. Thus the permeability curve of unsaturated soils has the similar shape with the soil-water characteristic curve(SWCC). Therefore, the methodologies have been studied to simply predict the unsaturated permeability from the SWCC. In this study, the experimental tests of SWCC and permeability were carried out for domestic weathered granite soils. The SWCC test results were fitted to Fredlund and Xing's SWCC equation and then it was found that there are some relationships between the parameters of SWCC equation and the basic soil properties. Accordingly we used an ANN(artificial neural network) model to obtain the SWCC parameters from the basic soil properties. Finally, the coefficients of permeability were predicted from these results by a prediction model.

• 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 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.