• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.21 no.10
• /
• pp.23-29
• /
• 2020

The soil structures settle down continuously under cyclic dynamic loading after opening railway lines. This study examined the characteristics of the settlement and stiffness of cement-treated soils with the change in the content of fines under cyclic dynamic loading. Eighteen cases of the test were carried out with the changes in the fines content of soils, cement content, and curing days. Based on the test results, cement-treated soils containing more than 3% of cement could decrease settlement sufficiently even with a high portion of fines under cyclic dynamic loading. In addition, the elastic and plastic settlements could be reduced using 3 to 4% cement to the level of 1/4 and 1/6, respectively. In the viewpoint of stiffness, the resilient modulus of cement-treated soils increases with increasing cement content. Using more than 3% of cement, the 80MPa compaction stiffness standard for the upper subgrade of railways was satisfied, even with 40% of fines content of soils.

• Journal of the Korean Geotechnical Society
• /
• v.31 no.3
• /
• pp.27-38
• /
• 2015

Triaxial tests on sand-silt mixture specimens under low and high confining pressures were performed to understand their shear behaviors. The fines content in the mixture is lower than the threshold value. A series of tests under different conditions including fines contents (0%, 9.8%, 14.7%, 19.6%), density of specimen (controlled by different compaction energies of $E_c=22kJ/m^3$, $E_c=504kJ/m^3$), confining pressure (100 kPa, 1 MPa, 3 MPa, 5 MPa) were performed to investigate influences of these factors. Based on the test results, the threshold fines content, where the dominant structure of mixture changes from sand-matrix to fines-matrix, decreases with the increase of confining pressure. Under very high confining pressures, as a result of sand particle crushing, the behavior of the dense specimen is similar to that of the loose specimen which shows hardening, compression behavior, and shear strength increases with increase of fines content. In conclusion, silt is granular material like sand, and its influence on shear behavior of sand-silt mixture is very different from that of plastic fines on sand-fines mixture.

• Journal of the Korean GEO-environmental Society
• /
• v.16 no.6
• /
• pp.31-38
• /
• 2015

Recently, the participation on the development of the natural gas pipeline in Russia as well as the recent construction of the second Korean Antarctic research station, the Jangbogo station provide the research interests on the behavior of the permafrost ground. To investigate the effect of fines on the mechanical responses of frozen sands, unconfined compression tests were performed on the frozen sands with 0, 5, 10 and 15% of fine contents at -5, -10 and $-15^{\circ}C$. The poorly graded (SP) Joomunjin sand and kaolinite, silt with low plasticity (ML) were used for the preparation of the frozen soil specimens. The mechanical responses of the tested soils were investigated via unconfined compression tests in the temperature controlled laboratory and analyzed in terms of peak unconfined compressive strength and secant modulus at 50% of the peak strength. As the fine contents increase, the unfrozen water contents increase and thus the strength and stiffness of frozen soils decrease. The increment of the stiffness and strength due to the temperature decrease vary with the fine contents.

• Journal of the Korean Geotechnical Society
• /
• v.37 no.7
• /
• pp.35-42
• /
• 2021

An experimental study was carried out on kaolinite-sand mixtures with various proportions of kaolinite content. To investigate physical behaviour of mixtures, index properties and compaction test results were analysed in various aspects. Moreover, to clearly see the interaction between kaolinite and sand particles, the observational analysis through microscopic image analysis device was conducted. The test results showed that an increase in the amount of kaolinite could create a strong bonding structure which resulted in higher specific surface available for activities of kaolinite particles. Also, an increase in the amount of the kaolinite resulted in an increase in the percentage of water sorption. Then it could accelerate the occupation rate of water which tended to take up the space that would have been occupied by solid particles, and accordingly, resulted in the decreased maximum dry unit weight and increased initial void ratio. Based on the microscopic image analysis, the samples were individually classified into three types of mixture such as sand dominant, intermediate fine content, and fine dominant. In addition, the fine and coarse grains seem to interact well in the mixtures with the fine content ranging from 25 to 40%.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.3C
• /
• pp.93-102
• /
• 2011

Most experimental studies on soil liquefaction are related to clean sands. However, soils in the field or reclaimed grounds commonly contain some amounts of silt and clay rather than clean sand only. Many researchers investigated the effect of fine contents on liquefaction resistance and mainly used non-plastic fines such as silts. In this study, 10% of plastic fines with various plasticity index (PI) such as 8, 18, 50, and 377 were mixed with wet Nakdong River sand and then loose, medium, and dense specimens were prepared by undercompaction method. A series of undrained cyclic triaxial tests were carried out by applying three different cyclic stress ratios. As a result, the liquefaction resistance tended to decrease as a PI of fines in the specimens with equal fine content increased. On the other hand, the difference between loose specimens with low and high plasticity fines was not clearly observed in terms of liquefaction resistance. However, in the case of dense specimens, liquefaction resistance decreased up to 40% as a plasticity of fines increased.

• Journal of the Korean Geotechnical Society
• /
• v.21 no.9
• /
• pp.53-64
• /
• 2005

For geotechnical design in practice, soils are, in general, assumed to behave as a linear elastic or perfect plastic material. More realistic geotechnical design, however, should take into account various factors that affect soil behavior in the field, such as non-linearity of stress-strain response, stress history, and water content. In this study, a series of laboratory tests including triaxial and resonant column tests were peformed with sands of various silt contents, relative densities, stress states, OCR and water contents. This aims at investigating effects of various factors that affect strength and stiffness of sands. From the results in this study, it is found that the effect of OCR is significant for the intermediate stress-strain range from the initial to failure, while it may be ignored for the initial stiffness and peak strength. For the effect of water content, it is observed that the initial elastic modulus decreases with increasing water content at lower confining stress and relative density At higher confining stresses, the effect of water content Is found to become small.

• Journal of the Korean GEO-environmental Society
• /
• v.22 no.6
• /
• pp.17-26
• /
• 2021

Ground investigation and result analysis generally used to examine all sorts of structures' subsidence or stability can be classified into sandy soil and cohesive soil, and analysis on the liquid limit of soil is utilized to evaluate the physical properties of ground and types or technical behavior of soil. The most widely used method to analyze liquid limit is Casagrande with which liquid limit can be calculated relatively easily; however, it is fairly difficult to apply it to soil equipped with intermediate properties. Therefore, concerning the properties of soil having the intermediate properties of sedimentary ground, this researcher mixed the clay from Yangsan, Gwangyang, and Busan with sandy soil to make intermediate soil and then carried out the test of consistency limit and also evaluated applicability by using the suggested formula of consistency revision. The sample of intermediate soil was the mixture of clay and sandy soil, and to produce intermediate soil, the content (F_c) of fine soil was applied as 50%, 75%, or 100%. Regarding the physical properties of intermediate soil, to maintain the properties of clay in the natural state, bentonite was added at a fixed rate for controlling the properties of clay, and then, consistency was analyzed. By adopting the formula of consistency revision suggested in advanced research, this author analyzed consistency based on the experiment and consistency based on the suggested formula of revision. Also, about intermediate soil collected at the site, consistency based on the experiment and consistency based on the suggested formula of revision were analyzed comparatively, and about intermediate soil collected, this researcher analyzed particle size and calculated the content (F_c) of fine soil to analyze intermediate soil in diverse conditions. Moreover, about intermediate soil collected at the site, the suggested formula of consistency revision was applied to calculate the compression index, and the compression index based on the experiment and the compression index based on the suggested formula were analyzed comparatively to evaluate the applicability of the suggested formula.

• Journal of the Korean Geotechnical Society
• /
• v.33 no.12
• /
• pp.7-20
• /
• 2017

In this study, effects of grain size distribution on the shear strength and rheological properties are investigated for coarse- and fine-grained soils by using direct shear apparatus. Shear strengths are estimated for fine-grained soils with the maximum particle size of 0.075 mm and coarse-grained soils with the maximum particle size of 0.425 mm and fine contents of 17% prepared at dry and liquid limit states. The direct shear tests are conducted under the relatively slow shear velocity, which corresponds to the reactivated landslide or debris flow after collapse according to the landslide classification. In addition, for the evaluation of rheological properties, residual shear strengths for both fine- and coarsegrained soils prepared under liquid limit states are obtained by multiple reversal shear tests under three shear velocities. From the relationship between residual shear strengths and shear rates, Bingham plastic viscosity and yield stress are estimated. The direct shear tests show that cohesions of fine-grained soil are greater than those of coarse-grained soil at both dry and liquid limit states. However, internal friction angles of fine-grained soil are smaller than those of coarse-grained soil. In case of rheological parameters, the plastic viscosity and yield stress of fine-grained soils are greater than those of coarse-grained soils. This study may be effectively used for the prediction of the reactivated landslide or debris flow after collapse.