• Journal of the Korean Geotechnical Society
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• v.29 no.7
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• pp.57-74
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• 2013

In this study, the virtual fixed point analysis and 3D full-modeling analysis for pile bent structures are conducted by considering various influencing factors and the applicability of the virtual fixed point theory is discussed. Also, a discrete analysis calculating separately both the superstructure and substructure of pile bent structures is performed on the basis of an equivalent base spring model by taking into account the major influencing parameters such as soil conditions, combined loading and pile diameter. The results show that the settlement and lateral deflection of the virtual fixed point theory are smaller than those of 3D full-modeling analysis. On the other hand, the virtual fixed point analysis overestimates the axial force and bending moment compared with 3D full-modeling analysis. It is shown that the virtual fixed point analysis cannot adequately predict the real behavior of pile bent structures. It is also found that discrete analysis gives similar results of lateral deflection and bending moment to those of unified analysis. Based on this study, it is found that discrete analysis considering column-pile interaction conditions is capable of predicting reasonably well the behavior of pile bent structures. It can be effectively used to perform a more economical design of pile bent structures.

• Journal of the Korean Geotechnical Society
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• v.34 no.6
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• pp.5-16
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• 2018

In this study, the large scale laboratory model tests were executed to investigate the lateral resistance characteristics of $2{\times}2$ group pile under lateral loads according to the array method and installation angle of piles. The effect on the behavior of $2{\times}2$ group pile was also investigated through model tests varying the pile diameter and length, distance to pile top from the ground surface, center-to-center (CTC) length and surcharge etc. From these test results, it was found that the lateral resistance of $2{\times}2$ group pile of which piles were constructed slantly in both directions was greater than that of group pile of which piles were constructed vertically. And as a result of parameter tests on the lateral resistance of $2{\times}2$ group pile, it was found that the most important parameter was the pile length. As the embedment depth ratio (L/D) increased to 36.5 from 26.5, the lateral resistance increased 3~4 times or more. But the center-to-center (CTC) length, distance to pile top from the ground surface and surcharge did not affect much on the lateral resistance of group pile.

• Geotechnical Engineering
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• v.11 no.4
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• pp.37-48
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• 1995

The dynamic behavior of dry sand under different vibration conditions is studied through laboratory experiments. Sinusoidal and random vibration experiments of sand are carried out in vertical direction under various surcharge loads. Five different sand samples are selected for the azperiment. They are composed of four different -size samples of particles and one sample which is simulated the field condition. In case of sinusoidal vibration, the change in relative density is measured with acceleration levels. To produce an acceleration, the vibration amplitude is maintained within the range of 0.4mm~0.6mm and the vibration frequency is changed within the range of 3Hz~40Hz. In case of random vibration, the combined sinusoidal acceleration is produced by a random vibration generator and the change in relative density is measured by an accelerometer. Based on the experimental results, it is found that the sandy soil is compacted to 94%~99% of relative density by vertical acceleration and the peak acceleration producing the maximum relative density is proportional to the difference between maximum and minimum void ratios. It is also found that the effect of surcharge loading : the greater the surcharge loading, the larger the change in relative density and the greater the acceleration required to change the relative density.

• Journal of the Korean Geotechnical Society
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• v.19 no.3
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• pp.53-64
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• 2003

Many transmission towers, high-rise buildings and bridges are constructed near steep slopes and are supported by large-diameter piles. These structures may be subjected to large lateral loads, such as violent winds and earthquakes. Widely used types of foundations for these structures are pier foundations, which have large-diameters with high stiffness. The behavior of a pier foundation subjected to lateral loads is similar to that of a short rigid pile because both elements seem to fail by rotation developing passive resistance on opposite faces above and below the rotation point, unlike the behavior of a long flexible pile. This paper describes the results of several numerical studies performed with a three-dimensional finite element method (FEM) of model tests of a laterally loaded short pile located near slopes, respectively. In this paper, the results of model tests of single piles and pile groups subjected to lateral loading, in homogeneous sand with 30$^{\circ}$ slopes and horizontal ground were analyzed by the 3-D FE analyses. The pile was assumed to be linearly elastic. The sand was assumed to have non-associative characteristics, following the MC-DP model. The failure criterion is governed by the Mohr-Coulomb equation and the plastic potential is given by the Drucker-Prager equation. The main purpose of this paper is the validation of the 3-D elasto-plastic FEM by comparisons with the experimental data.

• Journal of the Korean Geotechnical Society
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• v.18 no.5
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• pp.7-18
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• 2002

Generally, natural soils are affected by one-dimensional consolidation so that the behavior characteristic could be somewhat different from the isotropic consolidation specimen. But, due to experimental difficulties and the lack of equipment, the isotropic triaxial tests are mainly performed in most lab. tests. So it seems to be very effective if it is possible to predict pore water pressure and undrained shear strength in the $K_o$ state as the results of isotropic triaxial consolidation test. In this study, isotropic triaxial consolidation test and $K_o$ triaxial consolidation test were performed and we obtained parameters related to pore water pressure ratio using the Hyperbolic model. And then we predicted the behavior of pore water pressure that occurred in the $K_o$ state from the results obtained in the isotropic triaxial cosolidation test through the equation suggested by Lo(1969). It is possible to seize the validity of Lo(1969) equation. Also, considering undrained shear strength obtained from consolidation method in relation with water content, we find that consolidation method have an effect on undrained shear strength. Finally, using the Wroth(1984) equation that is based on the theory of critical state, undrained shear strength in the $K_o$ state was predicted from that of the isotropic triaxial consolidation test. The usefulness of the equation was verified by comparing the predicted value with experimental results.

• Journal of the Korean Geotechnical Society
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• v.27 no.11
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• pp.5-15
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• 2011

This paper presents two analysis methods for characterizing the non-linear finite strain consolidation behavior of highly deformable dredged soil deposits along with the fundamental parameters obtained in the companion paper; that is, the zero effective stress void ratio, the non-linear relationships of void ratio-effective stress and void ratio-hydraulic conductivity. The simplified Morris's analytical solution (2002) and the widely recognized numerical program, PSDDF (primary Consolidation, Secondary Compression, and Desiccation of Dredged Fill) for both single and double drainage conditions are adopted in this paper to verify a series of laboratory experiments for self-weight consolidation of the Incheon clay and Kaolinite. The comparisons show that the analysis methods proposed herein can properly simulate the long-term non-linear finite strain consolidation behavior for dredged soils in the field. In addition, a case study for the artificial Craney Island has been conducted to illustrate the importance of obtaining appropriate non-linear finite strain consolidation parameters and the applicability of PSDDF in promoting dredged soil disposal.

• Journal of the Korean Geotechnical Society
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• v.29 no.2
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• pp.15-21
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• 2013

The analysis of long-term performance of pavement sections under wheel loads is normally conducted in two separated steps. First the resilient behavior of the pavement is calculated assuming the pavement is a layered or discrete elastic medium, and then the permanent deformation is evaluated based on empirical permanent displacement equations. Material properties required in both steps can be obtained from cyclic triaxial tests, in other words, resilient and permanent deformation tests. While this analytical approach is simple and convenient, it does not consider the modulus degradation caused by cyclic loads, and some types of reinforcements such as geosynthetic cannot be modeled in this type of analysis. A model for degraded secant modulus is proposed and suggested to be used for the analysis of permanent behavior of unpaved roadway sections. The parameter for suggested model can be obtained from cyclic triaxial tests, regular practice in pavement engineering. Examples to estimate the model parameters are presented based on both laboratory permanent deformation test and large-scale plate load test.

• Journal of the Korean Geotechnical Society
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• v.35 no.6
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• pp.39-48
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• 2019

This study investigated the lateral behavior of monopile embedded in the dry sand through cyclic lateral loading test using a centrifuge test. The sand sample for the experiment was the dry Jumunjin standard sand at 80% relative density and the friction angle of $38^{\circ}$. In the experimental procedure, firstly, it was determined the static lateral bearing capacity by performing the static lateral loading test to decide the cyclic load. This derived static lateral bearing capacity values of 30%, 50%, 80%, 120% were determined as the cyclic lateral load, and the number of cycle was performed 100 times. Through the results, the experiment cyclic p-y curve was calculated, and the cyclic p-y backbone curve by depth was derived using the derived maximum soil resistance point by the load. The initial slope at the same depth was underestimated than API (1987) p-y curves, and the ultimate soil resistance was overestimated than API (1987) p-y curves. In addition, the result of the comparison with the suggested dynamic p-y curve was that the suggested dynamic p-y curve was overestimated than the cyclic p-y backbone curve on the initial slope and soil resistance at the same depth. It is considered that the p-y curve should be applied differently depending on the loading conditions of the pile.

• Journal of the Korean Geotechnical Society
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• v.37 no.11
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• pp.71-81
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• 2021

The purpose of this study is liquefaction phenomenon was simulated using the 1g shaking table test. Analysis of liquefaction and Re-liquefaction behavior according to the ground conditions was analyzed when an embankment exists above the ground. The soil used in the experiment was silica sand and the ground composition was a liquefied layer of 50cm (Case 1), a non-liquefied layer of 17.5cm and a liquefied layer of 32.5cm (Case 2). The embankment was formed by fixing the height of 10cm and the slope of the slope at a ratio of 1:1.8. For seismic waves, excitation of a 5Hz sine wave was performed for 8 seconds, and a total of 5 case excitations were performed. In Case 1, it was confirmed that liquefaction occurred at all depths during the first vibration excitation at the free-field and that liquefaction did not occur at all depths except 5cm at the third vibration excitation. At the center of the embankment, liquefaction occurred up to a depth of 20cm during the first vibration excitation, and it was confirmed that liquefaction did not occur at all depths except for a depth of 5cm during the second vibration excitation.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.6
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• pp.559-575
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• 2021

Due to the increase in ground excavation work, the possibility of ground subsidence accidents is increasing. And it is very difficult to prevent these risk fundamentally through institutional reinforcement such as the special law for underground safety management. As for the various cases of urban ground excavation practice, the ground subsidence behavior characteristics which is predicted using various information before excavation showed a considerable difference that could not be ignored compared to the results real construction data. Changes in site conditions such as seasonal differences in design and construction period, changes in construction methods depending on the site conditions and long-term construction suspension due to various reasons could be considered as the main causes. As the countermeasures, the safety management system through various construction information is introduced, but there is still no suitable system which can predict the effect of excavation and risk assessment. In this study, a web-based system was developed in order to predict the degree of impact on the ground subsidence and surrounding structures in advance before ground excavation and evaluate the risk in the design and construction of urban ground excavation projects. A system was built using time series analysis technique that can predict the current and future behavior characteristics such as ground water level and settlement based on past field construction records with field monitoring data. It was presented as a geotechnical data visualization (GDV) technology for risk reduction and disaster management based on web-based system, Using this newly developed web-based assessment system, it is possible to predict ground excavation impact prediction and risk assessment.