• Journal of the Korean Geotechnical Society
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• v.29 no.9
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• pp.55-69
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• 2013

An alternative design method of existing methods based on elastic theory the design method of roadbed considering plastic deformation of roadbed and stress-strain at roadbed materials with the cyclic loading of trains passing. The characteristics of the developed design method considering traffic load, number of cyclic loading and resilience modulus of roadbed materials can evaluate elastic strain as well as plastic settlement with allowable design criteria. The proposed design method is applied to standard roadbed section drawing of HONAM high-speed railway considering design conditions such as allowable elastic and plastic settlement, train speed, the tonnage of trains. As a result, required levels of resilience modulus model parameter ($A_E$), unconfined compressive strength, types of soil material were evaluated.

• 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.

• Journal of the Korean Geosynthetics Society
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• v.11 no.3
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• pp.1-9
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• 2012

If the railways consisting of soil subgrade is applied to repetitive loading, elastic deformation and plastic deformation will occur at the same time. So the repeat traffic loading condition should be considered to predict the long-term deformation on railway roadbed. In this study, laboratory data from the repeated load triaxial tests and cylinder model test were used to predict accumulated settlement on railway foundation and results were analyed based on the nonliear models and stress state considered. It has proposed predict model using power function model on plastic settlement of roadbed materials.

• Journal of the Korean Society for Railway
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• v.11 no.3
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• pp.334-341
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• 2008

Ballast track needs maintenance works because it is supported by the compressible trackbed and subgrade layers. Maintenance works are essential to secure riding comfort and extend the life cycle of it. The necessities of maintenance works are determined from track irregularities measured by EM120. Track irregularities is the results of the track deformation. Therefore, it is natural to evaluate the cause of it. This paper focuses on the points the track irregularities come from the trackbed and the subgrade. Nondestructive techniques, such as Ground Penetrating Radar (GPR) and Portable Falling Weight Deflectometer (PFWD) are applied to evaluate the trackbed conditions, ballast layer thickness and vertical track stiffness, in the test section 500m long of Gyungbu line. The trackbed investigation results are compared with the track irregularities measured by EM120 and maintenance works. Conclusively, it was found that some maintenance works were unnecessary on the test section.

• Proceedings of the KSR Conference
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• 1998.05a
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• pp.588-595
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• 1998

The purpose of this study is to perform development of techniques for reduction of ground vibration caused by highspeed railway. At the first year, we have researched for the statically and dynamically characteristics of materials that could reduce the propagated ground vibration. The tire chip and blast furnace slag had been selected as the reduction material. And we have tested these materials by computer analysis.

• Proceedings of the KSR Conference
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• 2002.05a
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• pp.283-288
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• 2002

The heavy downpour caused by unusual weather has destroyed a railroad bed. It caused a large amount of soil loss due to soil erosion. Hence, there is necessary to rehabilitate the destructed railroad bed as quickly as possible. Application of geotextile bag can standardize the rehabilitation process. Geotextile bag method can be more stable, faster, and more economical. In this study, the stress to geotextile bag was estimated to select the appropriate geotextile material. Geotechnical characteristics of geotextile were also determined.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.1747-1755
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• 2008

Design of the reinforced roadbed thickness is concerned with safe operation of trains at specified levels of speed, axle load and tonnage. There are two methods for evaluating it. One is using an experimental equation and the other is using elastic theory with considering axle load, material properties of subsoils and allowable elastic settlement. Multi-layered theory is used to determine reinforced roadbed thickness by RTRI. Although their reinforced roadbed thickness is designed with an objective of achieving a minimum standard 2.5mm of settlement on the subgrade surface, it is hardly applied to real design. Li(1994) has suggested the experimental model which design approach is to limit plastic strain and deformations for the design period. It is worth due to adopting soil equivalent number of repeated load application. Moreover, it has been a more advanced method than existing design methods because including resilient modulus of subsoil beneath track, soil deviator stress caused by train axle loads and MGT. In this paper, it is analyzed under domestic track conditions to estimate the reinforced roadbed thickness with different soil types.

• Journal of the Korean Society for Railway
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• v.5 no.2
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• pp.70-76
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• 2002

In this study, performance of reinforced railroad roadbeds with the reinforced roadbed materials were investigated through the real scale roadbed tests. It was also found that the reinforced roadbed with reinforced roadbed materials has less elastic and plastic settlement than the one with soil. The slag roadbed was more effective than the crushed stone roadbed with the same condition for load distribution. Therefore considering overall characteristics of reinforced roadbed material, the optimum thickness was recommended as 50 cm. Furthermore the real scale model test under the simulated rainfall condition, the settlement in the slag roadbed was about 8 times smaller than the settlement in the soil roadbed.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.191-198
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• 2000

Dynamic fatigue test is carried out using soil model box for the evaluation of performance of three different roadbed materials. Bearing capacity, settlement and mud pumping phenomenon of each roadbed materials as well as penetration of model ballast into the roadbeds are investigated. It was found that settlement of slag and crushed stone roadbed is smaller than the soil roadbed during dynamic fatigue test with same initial conditions.

• Journal of the Korean Geosynthetics Society
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• v.4 no.4
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• pp.3-11
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• 2005

In this study, a large-scale laboratory model test and 2-D numerical analysis were conducted to verify the reinforcement effect by utilizing geotextile bag on the railway roadbed. Static loading which simulated train load was applied on the geotextile-reinforced railway roadbed and also unreinforced railway roadbed. Computer program named Pentagon 2-D which is a part of FEM programs was used in the numerical analysis. Based on the results of laboratory test and 2-D numerical analysis, the effect of load distribution and settlement reduction was found to be depending on the geotextile characteristics, tensile strength of geotextile, and interface friction angle between geotextile bags. In general, the result of 2-D numerical analysis shows lower value than that of laboratory test.