• Journal of Korean Tunnelling and Underground Space Association
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• v.12 no.2
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• pp.117-127
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• 2010

Gound excavation is frequently executed in unsaturated soil conditions. In this paper, the effect of apparent cohesion in unsaturated soils on the ground behavior during underground excavation is studied. The VPPE (Volumetric Pressure Plate Extractor) test, the unsaturated triaxial test and the trap-door test were carried out to figure out how the behavior of soils varies depending on the variation of apparent cohesion. The test results show that the ground behavior is almost identical if the soil is either fully dry or fully saturated. However, if the soil is partially-saturated with the increase of water content, the ground behaves quite differently. In summary, the apparent cohesion in unsaturated soils plays key roles when excavating underground structures.

• The Journal of Engineering Geology
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• v.21 no.2
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• pp.157-162
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• 2011

Experimental tests have been performed to measure the thermal conductivity of unsaturated soils, and computational models have been widely used to predict thermal conductivity. However, measured values of the thermal conductivity of unsaturated soils cannot be compared with predicted values because of the gradient in moisture content within unsaturated soils. In this study, experimental consolidation tests on saturated unfrozen kaolinite were performed to investigate the effect of dry density and moisture content on thermal conductivity. The results were used to evaluate the validity of a model employed to calculate thermal conductivity.

• Geomechanics and Engineering
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• v.33 no.6
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• pp.625-633
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• 2023

The volume changes associated with moisture or suction variation in expansive soils are of geotechnical and geoenvironmental design concern. These changes can impact the performance of infrastructure projects and lightweight structures. Assessment of unsaturated function for these materials leads to better interpretation and understanding, as well as providing accurate and economic design. In this study, expansive soils from different regions of Saudi Arabia were studied for their basic properties including gradation, plasticity and shrinkage, swelling, and consolidation characteristics. The unsaturated soil functions of saturated water content, air-entry values, and residual states were determined by conducting the tests for the entire soil water characteristic curves (SWCC) using different techniques. An attempt has been made to provide a prediction model for unsaturated properties based on the basic properties of these soils. Once the profile of SWCC has been predicted the time and cost for many tests can be saved. These predictions can be utilized in practice for the application of unsaturated soil mechanics on geotechnical and geoenvironmental projects.

• Proceedings of the Korean Society for Agricultural Machinery Conference
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• 1993.10a
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• pp.1036-1042
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• 1993

In order to derive homogeneous remould soil sample, which is very important for obtaining reliable experimental results in terra-mechanics research, the characteristics of two clay soils at high moisture contents after remoulding treatment were investigated . It was found that with the remoulding process employed the coefficients of variation was less than 1.2% for the soil density and the soil could be treated as fully saturated soil. Therefore, the remoulded and will restore after a period of time. Some suggestiions were given follow the results of the drop cone test.

• Proceedings of the KSR Conference
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• 2002.05a
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• pp.264-270
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• 2002

The frost heaving pressure can be a problem for weakening of the railroadbed material. In this study, upon freezing a saturated soil in a closed-system from the top, a considerable pressure was developed. This pressure is induced as a result of a curved ice-water interface. This study was initiated to investigate the soils frost heaving expansion pressure and physical characteristics resulting from freezing and freezing-thawing cycle process. Weathered granite soils, sandy soil were used in the laboratory freezing test subjected to thermal gradients under closed-systems.

• Proceedings of the Korean Geotechical Society Conference
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• 2002.03a
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• pp.329-336
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• 2002

The earth structures and in-ground LNG tank, and buildings can be constructed with using artificial freezing method on the reclaimed land. In this study, upon freezing a saturated soil in a closed-system from the top, a considerable pressure was developed. The pressure is the result of the surface energy of a curved ice-water interface. The most significant of these parameters will have the greatest effect on the classification. In order to establish frost-susceptibility criteria based on frost heaving expansion pressure, more soils have to be tested. This study was initiated to investigate the soils frost heaving expansion pressure and moisture characteristics resulting from freezing and freezing-thawing cycle process. Weathered granite soils, sandy soil, sandy soil were used in the laboratory freezing test subjected to thermal gradients under closed- systems.

• Geomechanics and Engineering
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• v.25 no.4
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• pp.283-294
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• 2021

This paper presents a rigorous solution for spherical cavity expansion in unsaturated soils under constant suction condition. The hydraulic behavior that describes the saturation-suction relationship is modeled by a void ratio-dependent soil-water characteristic curve, which allows the hydraulic behavior to fully couple with the mechanical behavior that is described by an extended critical state soil model for unsaturated soil through the specific volume. Considering the boundary condition and introducing an auxiliary coordinate, the problem is formulated to a system of first-order differential equations with three principal stress components and suction as basic unknowns, which is solved as an initial value problem. Parameter analyses are conducted to investigate the effects of suction and the overconsolidation ratio on the overall expansion responses, including the pressure-expansion response, the distribution of the stress components around the cavity, and the stress path of the soil during cavity expansion. The results reveal that the expansion pressures and the distribution of the stress components in unsaturated soils are generally higher than those in saturated soils due to the existence of suction.

• Journal of the Korean Institute of Landscape Architecture
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• v.34 no.4 s.117
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• pp.96-104
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• 2006

Impervious pavement is primary contributor to the malfunctioning of the urban water circulation system. The aim of this research is to provide basic information and data for new pavement materials and paving technology which could enhance the urban water circulation system. For the study purposes, physical properties of soils sampled from 16 stations were analyzed. The sampling spots were paved with grass block porous pavement material. The findings from the analysis are as follows. The hardness of soils under the pavement was $17{\sim}22mm$ for thoroughfare and $6{\sim}32mm$ for parking areas. The bulk density was $1.42{\sim}1.81g/cm^{3}$ for thoroughfare and $1.38{\sim}1.75g/cm^{3}$ for parking area. The solid phase ration was $46.9{\sim}62.5m^{3}/m^{3}$ for thoroughfare and $45.6{\sim}61.3m^{3}/m^{3}$ for parking area. The porosity was $37.5{\sim}53.1m^{3}/m^{3}$ for thoroughfare and $38.7{\sim}54.4m^{3}/m^{3}$ for parking area. The saturated hydraulic conductivity was $8{\sim}164mm/hr$ for thoroughfare and $14{\sim}201mm/hr$ for parking area. The saturated hydraulic conductivity of the H sample area (the area was completed three months ago) and that of the other area were compared. There was up to 80% decreases of the saturated hydraulic conductivity within one year after the completion of pavement. After the first year, decrease in the saturated hydraulic conductivity was modest. Also there are changes in both surface and under soil physical properties of the grass block porous pavement depending on compaction. The extent of change depends on the degree of compaction. All these factors are combined to influence the permeability of the soil under the pavements. The results of this suggest that it is required to develop a new pavement technology which ensures both the durability and porosity of the pavement to improve the water circulation system by applying Ecological Area Rate.

• Journal of the Korean Geotechnical Society
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• v.25 no.1
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• pp.65-76
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• 2009

The unsaturated characteristics of Korean weathered granite soils have been studied to investigate the influence of saturated permeability, rainfall intensity and soil-water characteristic curve (SWCC) on the slope stability. The upper, average and lower SWCCs were estimated from the publication and experimental results using the statistical concept. The roughly estimated SWCC can be used for the soils without experimental results by relating SWCC with the particle size distribution curve. An appropriate ratio between the saturated permeability and the rainfall intensity ($k_s$/i) was also suggested for practical use in designing the slopes by investigating the time-dependent variation of slope instability during the rainfall. The slope stability was deteriorated from the initiation of rainfall and recovered again after the factor of safety reached the critical value. The FS of the slope decreased at first and then increased after reaching the critical value during the rainfall. As a result, the slope instability was not related with an absolute rainfall intensity but with the ratio between the saturated permeability and the rainfall intensity. In case of the upper SWCC, the critical condition occurred when the ratio between the saturated permeability and the rainfall intensity was in the range of $1.0{\sim}2.0$.

• Korean Journal of Soil Science and Fertilizer
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• v.43 no.1
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• pp.1-7
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• 2010

This study was carried out to investigate plow pan characteristics and to grasp the relationship between its particle size distribution fractal dimension ($D_m$) and water transport in paddy plow pan. Twenty four soil sampling sites with different management groups, ordinary and sandy-textured, were selected and investigated for physical properties of soils such as Yamanaka hardness in April, non-submerged condition, before rice seedling transplanting. The plow pan appearing depth and thickness was determined by penetration resistance profile. Undisturbed core samples with five replicates were sampled at plow pan layerwith 2 inch cores for measuring soil bulk density and saturated hydraulic conductivity. The particle size distribution fractal dimension ($D_m$) was calculated by the method following the procedure Tylerand Wheacraft (1992), using the USDA-based particle size analysis datawith fractions of 0-0.002, 0.002-0.053, 0.053-0.1, 0.1-0.25, 0.25-0.5, 0.5-1.0, and 1.0-2.0 mm. The plow pan of investigated fields appeared at a range from 5 to 30 cm depth, showing minimum value in sandy-textured management group and maximum value in ordinary management group. The thickness of plow pan were distributed from 5 to 17 cm, showing both minimum and maximum values in sandy-textured management group. Averagely, the plow appearing depth were deeper in ordinary management group than in sandy-textured management group, whereas the reverse in the thickness of plow pan. The particle size distribution fractal dimension ($D_m$) had higher value with finer textures, with higher fractality in coarser texture. Saturated hydraulic conductivities, $K_s$, of plow pan soils distributed from 0.5 to 1420 mm $day^{-1}$, having the highest value in sandy skeletal soils. The $K_s$ decreased with decreasing clay content and $D_m$, showing power function relationships. The coefficient of determination, $R^2$, of the fitted power functions were higher in $D_m$ as x-axis than in clay content. This means that $D_m$ could give us more effective estimation than clay content. Especially, sandy-textured paddy soils had higher $R^2$, compared to ordinary paddy soils. $K_s$ of relatively coarse-textured soils with less than 18%of clay content, therefore, was more dependent on particle size distribution than that of relatively fine-textured soils. From these results, it could be concluded that the fractal scaling gives us a unique quantity describing particle size distribution and then can be applied to estimate saturated hydraulic conductivity, especially more effective in coarse-textured soils.