• Journal of the Korean Geotechnical Society
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• v.19 no.2
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• pp.7-14
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• 2003

A series of laboratory tests, which can show how different curing conditions influence an aging effect on clay, were carried out for the clay samples collected in the area of Kwangyang Bay and Mokpo. Clay samples were remolded and reconsolidated under three different curing temperatures (20, 50, and 80 degree Celsius) and low different curing durations (1, 7, 14, and 40 days). To find out an aging effect and geotechnical characteristics between undisturbed samples and reconsolidated samples, laboratory tests, consisting of uniaxial compression tests, CU triaxial test, and consolidation tests, were preformed. Results showed that the compression index ratio is very useful factor to indicate the aging effect of natural clays. Also geotechnical characteristics of clays reconsolidated at high temperature were very similar to those of undisturbed clays. Finally, curing temperature and curing duration influenced an aging effect on clays. The best curing condition was 80 degree Celsius and 27 days.

• Journal of the Korean Geotechnical Society
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• v.39 no.3
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• pp.17-27
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• 2023

In order to accurately determine soil characteristics, it is necessary to collect undisturbed samples, and it is important to collect these samples with minimal disturbance. In this study, a sampler that minimizes sample disturbance was developed by attaching a catcher to the tip, and its applicability was reviewed through in situ sampling, X-ray CT, and laboratory tests. Results confirmed that horizontal cracks are likely to occur when using the Shelby tube sampler, whereas these cracks can be suppressed when using the newly developed sampler. Moreover, consolidation and shear test results showed that the samples collected using the newly developed sampler showed higher maximum shear strength compared to those collected using the Shelby tube sampler.

• Geomechanics and Engineering
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• v.5 no.1
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• pp.57-70
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• 2013

Constant rate of strain (CRS) consolidation tests were conducted for undisturbed Ariake clay samples from three boreholes in Saga Plain of Kyushu Island, Japan. The coefficients of consolidation ($c_{\nu}$) were interpreted from the CRS test results by small- and large-strain theory. Large-strain theory was found to interpret smaller $c_{\nu}$ values and less strain rate effect on $c_{\nu}$ than that by small-strain theory. Comparing the theoretical strain distributions within a soil specimen to those obtained by numerical simulation shows that the small-strain theory can be used only for the dimensionless parameter $c_{\nu}/\dot{\varepsilon}H_0^2{\geq}50$ (where $\dot{\varepsilon}$ is strain rate and $H_0$ is the specimen height), and the large-strain theory can be used for a larger range of strain rates. Applying the criterion to undisturbed Ariake clay with a $c_{\nu}$ value of about $1{\times}10^{-7}\;m^2/s$, it is suggested that the large-strain theory should be adopted for calculating the $c_{\nu}$ value when $\dot{\varepsilon}$ > 0.03%/min.

• 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.

• The Journal of Engineering Geology
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• v.7 no.3
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• pp.217-227
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• 1997

The purpose of this study is to analyze the correlation of soil properties in coastal soft ground. For the purpose of this study, several coastal soft ground areas were selected. Many large scale construction works are being executed and will increase continuously in these soft ground areas. So, soil property in these areas is very important. The grounds forming coastal areas are affected by seawater movement. So, most of these areas consist of alluvium stratum. Therefore, soil properties of eastern and southern coastal areas are very complex. Many laboratory tests were executed with disturbed and undisturbed soil samples. Undisturbed samples were taken by using thin walled tubes and transported into the laboratory with caution, so as not to disturb the sample. The consistent rate of fine-grained content in these areas is over 90%. Also, these areas contain higher water content and clay content. Therefore, knowing these soil properties, it is possible to safely design fabrics and constructions.

• Journal of Navigation and Port Research
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• v.36 no.3
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• pp.181-187
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• 2012

Highly plastic clays in their normally consolidated states are not always linear but are concave downwards. Thus their compression index deceases with the increase of consolidation pressure. The $e-{\log}{\sigma}_{\upsilon}{\prime}$ curves of plastic or non-plastic silty clays are not linear but are convex upwards. In this paper, consolidation tests were conducted with several undisturbed field soils of Korea south coast and their $e-{\log}{\sigma}_{\upsilon}{\prime}$ plots are not always linear. In case of using Butterfield's method(liquid limit 50~100%), ${\ln}{\upsilon}-{\ln}{\sigma}_{\upsilon}{\prime}$ plots are linear. But some undisturbed samples which have void ratio over 2.24, liquid limit over 100% and plasticity index over 60% are not linear. In results of consolidation tests with remolded samples which contain silt(fly ash) contents of 90% has compression index increasing with the increase in consolidation pressure.

• Geomechanics and Engineering
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• v.5 no.6
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• pp.575-594
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• 2013

Organic soils exhibit problematic properties such as high compressibility and low shear strength; these properties may cause differential settlement or failure in structures built on such soils. Organic soil removal or stabilization are the most important methods to overcome geotechnical problems related to peat soils' engineering characteristics. This paper presents soil mechanical intervention for stabilization of peat with sand columns and focuses on a comparison between the mechanical characteristics of undisturbed peat and peat stabilized with 20%, 30% and 40% of sand on the laboratory scale. Cylindrical columns were extruded in different diameters through a nearly undisturbed peat sample in the laboratory and filled with sand. By adding sand columns to peat, higher permeability, higher shear strength and a faster consolidation was achieved. The sample with 70% peat and 30% sand displayed the most reliable compressibility properties. This can be attributed to proper drainage provided by sand columns for peat in this specific percentage. It was observed that the granular texture of sand also increased the friction angle of peat. The addition of 30% sand led to the highest shear strength among all mixtures considered. The peat samples with 40% sand were sampled with two and three sand columns and tested in direct shear and consolidation tests to evaluate the influence of the number and geometry of sand columns. Samples with three sand columns showed higher compressibility and shear strength. Following the results of this laboratory study it appears that the introduction of sand columns could be suitable for geotechnical peat stabilization in the field scale.

• Geomechanics and Engineering
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• v.22 no.2
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• pp.165-171
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• 2020

Laboratory determination of strength and deformation behavior of clean sands and gravels has always been challenging due to the difficulty in obtaining their undisturbed samples. An alternative solution to this problem is to develop correlations between mechanical properties of cohesionless soils and their gradation characteristics. This study presents database of 3 natural sands with 11 varying particle size gradation curves to allow investigating relationships between mean particle size, maximum and minimum void ratio, relative density and shear strength of the test soils. Direct shear tests were performed at relative densities of 50, 75 and 95% to explore the effects of gradation and density on the angle of internal friction of the modeled sand samples. It is found that the mean grain size D₅₀ bears good correlations with void ratio range (e_max - e_min) and peak angle of internal friction 𝜙'_peak. The generated regression models are in good agreement with published literature and can be considered as reliable for natural sands in Pakistan. These empirical correlations can save considerable time and efforts involved in laboratory and field testing.

• Proceedings of the Korean Geotechical Society Conference
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• 2008.03a
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• pp.318-326
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• 2008

Recently, a new seismic probe, called "MudFork", has been developed and can be utilized for accurate and easy measurements of shear wave velocities of soft soils. To expand its use to estimate undrained shear strength and density, correlations between those and shear wave velocity were being attempted. Cone penetration tests and a seismic test, using MudFork, were performed at a soft ground site near Incheon, Korea. Also, undisturbed samples were obtained and shear wave velocities of the samples were measured as well as undrained shear strength, using triaxial compression test and bender elements. A simple linear relationship between shear strength and shear wave velocity was obtained, and a tentative relationship between density and shear wave velocity was also defined.

• Geotechnical Engineering
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• v.12 no.5
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• pp.17-26
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• 1996

The undrained behavior of Asan marine soil was investigated by using an automated triaxial testing device. The stress-strain behavior at the preand postfailure state of marine soil under undrained compression and eatension conditions was compared with the behavior of pure silt, pure clay and the overall behavior of Asan marine soil was predicted with the modified Camflay model and the bounding surface model. The marine soil sampled in Asan bay area was clayey silts with 70oA silt-30% clay content and the testing samples were prepared in both undisturbed and remolded conditions. All samples are normally consolidated with 400 kPa of effective mean confining pressure and each sample is unloaded to 200, 100, 67 kPa, respectively. And then the shear test was performed with different confining pressure. According to experimental results, there exists an unique failure line whose slope is lower than silt's and higher than clay's. It is identified that the undrained shear strength of normally consolidated samples increases after crossing the phase transformation line because of volume dilation tendency which is not seen in clay. Overconsolidated samples show different soil behavior compared with pure silt due to its tendency of change in volume. It is also found that the overall behavior of Asan marine soil cannot be predicted precisely with the modified Cam-clay model and the bounding surface model.