• Proceedings of the KSR Conference
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• 2007.11a
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• pp.480-493
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• 2007

Many railway-advanced countries are using the various types of track to reduce the track maintenance and repair cost according to the improvement of velocity. It spends on much maintenance and repair cost for ballast track due to abrasion of ballast, track irregularity and unisotropical ballast-support stiffness. The ballast track on railway bridge is accelerating the deterioration of ballast according to interaction of railway bridge and track. As continuing the deterioration, it is caused dynamic loads. Due to these effects, it increases negative loads of track and bridge. However, when designing the railway bridge, the effect of ballast track was applicate only dead load, so elastic behavior effect of ballast track is not influenced. Therefore, this paper presumes the stiffness of ballast track on railway bridge considering dynamic behavior of railway bridge, it was evaluated that effect on dynamic behaviors of railway bridge according to ballast track stiffness.

• Journal of the Korean GEO-environmental Society
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• v.19 no.4
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• pp.5-16
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• 2018

In the current study, the engineering behaviour of prebored and precast steel pipe piles was examined from a series of full-scale field measurements by conducting static pile load tests, dynamic pile load tests (EOID and restrike tests) and Class-A and Class-C1 type numerical analysis. The study includes the pile load - settlement relations, allowable pile capacity and shear stress transfer mechanism. Compared to the allowable pile capacity obtained from the static pile load tests, the dynamic pile load tests and the numerical simulation showed surprisingly large variations. Overall among these the restrike tests displayed the best results, however the reliability of the predictions from the numerical analysis was lower than those estimated from the dynamic pile load tests. The allowable pile capacity obtained from the EOID tests and the restrike tests indicated 20.0%-181.0% (avg: 69.3%) and 48.2%-181.1% (avg: 92.1%) of the corresponding measured values from the static pile loading tests, respectively. Furthermore, the computed results from the Class-A type analysis showed the largest scatters (37.1%-210.5%, avg: 121.2%). In the EOID tests, a majority of the external load were carried by the end bearing pile capacity, however, similar skin friction and end bearing capacity in magnitude were mobilised in the restrike tests. The measured end bearing pile capacity from the restrike tests were smaller than was measured from the EOID tests. The present study has revealed that if the impact energy is not sufficient in a restrike test, the end bearing pile capacity most likely will be underestimated. The shear stresses computed from the numerical analysis deviated substantially from the measured pile force distributions. It can be concluded that the engineering behaviour of the pile is heavily affected if a slime layer exists near the pile tip, and that the smaller the stiffness of the slime and the thicker the slime, the greater the settlement of the pile.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.1
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• pp.171-178
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• 1994

The skin friction on single piles was investigated by using an analytical study and a numerical analysis. The emphasis was given to the variation of skin friction on piles based on the load transfer mechanism developed for the consolidation of a surrounding soft clay. Local yield or slip at the pile-soil interface was taken into account by specifying a limiting value of shear stress. The response of a single pile was analyzed and compared to the results of field case study. Based on the results obtained, it is shown that the skin friction on a pile increases as the degree of consolidation increases and the ultimate axial forces result from the long term behavior of clay corresponding to the end of the consolidation. It is also found that the analysis using one-dimensional consolidation theory as well as two or three-dimensional non-linear analysis gives relatively reasonable results.

• Journal of the Korean Geotechnical Society
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• v.36 no.11
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• pp.7-20
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• 2020

In this study, the dynamic behavior of a single pile foundation was investigated by using an analytical and numerical studies. The emphasis was given on quantifying a function about the coefficient of dynamic horizontal subgrade reaction from 3D analysis. Based on the numerical analysis, a modified correction factor (α), which is used to obtain the coefficient dynamic horizontal subgrade reaction, was proposed by considering shear wave velocity of soil and confining stress. It was found that the prediction by pseudo-static analysis using the proposed coefficient is in good agreement with the general trends observed by dynamic analysis, and it represents a practical improvement in the prediction of behavior for pile foundations subjected to dynamic loads.

• Journal of the Korean Society for Marine Environment & Energy
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• v.19 no.1
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• pp.52-61
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• 2016

To inject huge amount of $CO_2$ for CCS application, high pressure pipeline transport is accompanied. Rapid depressurization of $CO_2$ pipeline is required in case of transient processes such as accident and maintenance. In this study, numerical analysis on the depressurization of high pressure $CO_2$ pipeline was carried out. The prediction capability of the numerical model was evaluated by comparing the benchmark experiments. The numerical models well predicted the liquid-vapor two-phase depressurization. On the other hands, there were some limitations in predicting the temperature behavior during the supercritical, liquid phase and gaseous phase expansions.

• Journal of the Korean Geotechnical Society
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• v.31 no.9
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• pp.5-15
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• 2015

In this study, rainfall-induced slope stability and coupling effect are investigated using hydro-mechanical finite element model. This model is developed by formulating constitutive and coupled balance equations and is verified by comparing the numerical results with field matric suction. The homogeneous soil layer (soil column) and soil slope are modeled by this model, and the results of variation in matric suction, mean effective stress, porosity, displacement, factor of safety are compared with those of staggered analysis. It is found that the vertical and horizontal displacement from coupling analysis considering change in porosity is larger than that of staggered analysis. The displacement and matric suction from coupling analysis by rainfall infiltration can affect slope instability, which shows a progressive failure behavior. The lowest factor of safety is observed under short-term rainfall. This results confirm the fact that coupling analysis is needed to design soil slope under severe rain condition.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.14 no.3
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• pp.565-572
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• 1994

Consolidation behavior on soft clay was investigated by using one- and two-dimensional analysis based on original and modified one dimensional consolidation theory. For the analytical model, the embankment was simulated by applying single- or multi-surcharge loading to the surface of soft clay. Based on the results obtained, it was found that the predicted settlement by one dimensional consolidation theory was most of the time higher than the observed one at the mid- and especially lateral-zone of embankment. When compared with two dimensional analysis, the result of modified one dimensional consolidation analysis showed almost similar trend to the observed one. There fore even in case where proper selection of soil parameters, one dimensional consolidation theory like as modified one dimensional consolidation theory could be suggested due to its convenience.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2008.05a
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• pp.321-327
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• 2008

Performance characteristics of the axi-symmetric supersonic exhaust diffuser (SED) with a second throat are numerically investigated. Computational strategy repeats those for a straight exhaust diffuser with zero-secondary flows. Renolds-Average Navier-Stokes equations with a standard ${\kappa}-{\varepsilon}$ turbulence model incorporated with standard wall function are solved to simulate the diffusing evolutions of the nozzle plume. The methodology is validated with accuracy. To predict the improvement of starting performance by second throat diffuser, diffuser characteristic curve due to the SED equipped with the second throat is speculated with respect to that of a straight area type as a function of nozzle stagnation pressure. Principal physics caused by the of the second throst is also addressed in terms of a second throat area ratio.

• Journal of the Korean Geotechnical Society
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• v.21 no.2
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• pp.127-135
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• 2005

In this paper, a numerical comparison of predictions by limit equilibrium analysis and finite difference analysis is presented for slope/soil-nail system. Special attention is given to the coupled analysis based on the explicit-finite-difference code, FLAC 2D. To this end, an internal routine (FISH) was developed to calculate a factor of safety for a soil nail slope according to shear strength reduction method. The case of coupled analyses was performed for soil nails in slope in which the soil nails response and slope stability are considered simultaneously. In this study, by using these methods, the failure surfaces and factors of safety were compared and analyzed in several cases, such as toe, middle and top of the slope, respectively. Furthermore, the coupled method based on shear strength reduction method was verified by the comparison with other analysis results.

• Journal of the Korean Geotechnical Society
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• v.33 no.4
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• pp.25-34
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• 2017

The soil-water characteristics is the most important state parameter for understanding changes in suction and water contents of unsaturated soil slopes. In the field, the hysteretic behaviors of drying and wetting soil-water characteristic curve are real and the adoption of path-dependent suction-water content is needed to predict the hydro-mechanical analysis of unsaturated soils. In this study, in-situ monitored hydraulic behavior of various soil slopes are compared with the data from numerical analysis with the laboratory soil water characteristic curve. Then, the verifications are performed based on the field monitored data respectively. Therefore, the use of path-dependent soil-water characteristic curves could be more rational for design and analysis of unsaturated soil slopes under rainfall conditions.