• Journal of the Korean Society for Railway
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• v.14 no.5
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• pp.433-441
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• 2011

It is a fact that the straightening of track alignment is one of the undoubted ways to improve the train speed on conventional lines, while that requires huge investment resources. Therefore, the operation of a tilting train as well as the minimum improvement of track is suggested as an effective and economical alternative way for the speed-up of conventional lines. Since a driving mechanism of tilting train is different from those of existing trains, in order to make sure its operation safety and stability on conventional line, the performance of track and roadbed must be preferentially evaluated on the conventional line. Furthermore, it is necessary to estimate the tilting-train-induced roadbed response in detail since the roadbed settlement can lead to the track deformation and even derailment. In this research, the patterns of wheel load and lateral force were monitored and analyzed through the field tests, and the derailment coefficient and degree of wheel off-loading were calculated in order to evaluate the tilting train running safety depending on the running speeds (120km~180km) on the conventional line. Moreover, roadbed pressure, settlement and acceleration were also observed as tilting-train-induced roadbed responses in order to estimate the roadbed stability depending on the running speeds. Consequently, the measured derailment coefficient and degree of wheel off-loading were satisfied with their own required limits, and all of the roadbed responses were less than those of existing high-speed train (KTX) over an entire running speed range considered in this study. As a result of this study, the tilting train which will be operated in combination with existing trains is expected to give no adverse impact on the conventional line even with its improved running speed.

• Journal of the Korean Society for Railway
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• v.14 no.1
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• pp.49-56
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• 2011

In this paper, it was compared the characteristics of the stress and settlement that occur from a track on the ground using a model test and has quantitatively analyzed the difference based on stress path and effect of the rotation of principal stress. Under identical roadbed conditions, the settlement generated by moving wheel loads were found to be 6 times and 3 times larger than that from static loads and cyclic loads, respectively. The deviator stress affecting shear deformation and the length of stress path generated by moving loads were twofold or greater increase than those by static loads. Furthermore, the stress path generated by moving loads was approached more closely to Mohr-Coulomb failure criteria compared to that by static loads. Also, it was found that ballasted track was occurred about 60% of maximum stress at $40^{\circ}$ of the rotation angle of principal stress and was affected with rotation of principal stress with moving wheel loading condition.

• Journal of Korean Society of Steel Construction
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• v.17 no.6 s.79
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• pp.673-679
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• 2005

According to continuous welded rails on a bridge, temperature changes bring about the expansion of the bridge deck,adding axial forces on the track. Moreover, the ballast on the bridge deck expansion joint is moved due to the bridge deck. The longer the bridge deck is, the greater the influence will be, loosening the ballast, causing track irregularities, and deteriorating passenger comfort. Considering the structure of the bridge itself and tolerance for track irregularities caused by the loosened ballast on the bridge, the maximum length of the deck should be less than 80 m, which is the same as the standard of French railways. In this study, the interaction between the expansion related to the bridge length and the irregularity in the longitudinal level, referring to measurements and maintenance work performed in high-speed railways, was analyzed. This research shows that the installation of a sliding plate or a vertical ballast stopper is not a good option, since it is difficult. On the other hand, the installation of a ZLR fastener or gluing is easy, but its influence is insignificant. In conclusion, switch tie tamping or manual tamping is more effective than other methods of what?

• Proceedings of the KSR Conference
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• 2011.10a
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• pp.406-411
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• 2011

An active application of tram is being expected in Korea in the near future. For the tram operation in urban area, the embedded rail tracks where rails are completely embedded with pavements is required. When the embedded rail track is constructed on fine-grained subgrade soil, excessive cumulative plastic settlements due to repetitive tram road may occur. In this study, repetitive load tests were carried out to evaluate the accumulative plastic settlements of subgrade soils underneath embedded rail tracks. Two real-scale track specimens of 5 m lengths were constructed considering the maximum cant of a curved line. Repetitive tram loads of three million times were applied to the tracks in 5 Hz frequency. The accumulating patterns of plastic settlements were analyzed. Tram load distributing effects of the concrete slabs were also evaluated using the measured data of earth pressures cells that were installed underneath track. Also the measured settlements were compared with the estimated settlements calculated from an existing experimental equations, and its validity is discussed.

• Structural Monitoring and Maintenance
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• v.4 no.3
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• pp.195-220
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• 2017

Nowadays, railway system plays a significant role in transportation, conveying cargo, passengers, minerals, grains, and so forth. Railway ballasted track is a conventional railway track as can be seen all over the world. Ballast, located underneath the sleepers, is the most important elements on ballasted track, which has many functions and requires routine maintenance. Ballast needs to be maintained frequently to prevent rail buckling, settlement, misalignment so that ballast has to be modelled accurately. Continuum model was introduced to model granular material and was extended in ballast. However, ballast is a heterogeneous material with highly nonlinear behaviour. Hence, ballast could not be modelled accurately in continuum model due to the discontinuities nature and material degradation of ballast. Discrete element modelling (DEM) is proposed as an alternative approach that provides insight into constitutive model, realistic particle, and contact algorithm between each particle. DEM has been studied in many recent decades. However, there are limitations due to the high computational time and memory consumption, which cause the lack of using in high range. This paper presents a review of recent ballast modelling with benefits and drawbacks. Ballast particles are illustrated either circular, circular crump, spherical, spherical crump, super-quadric, polygonal and polyhedral. Moreover, the gaps and limitations of previous studies are also summarized. The outcome of this study will help the understanding into different ballast modelling and particle. The insight information can be used to improve ballast modelling and monitoring for condition-based track maintenance.

• Proceedings of the KSR Conference
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• 2009.05b
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• pp.641-646
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• 2009

Concrete tracks are superior to ballast tracks in the aspect of durability, maintenance and safety. However, deteriorated stiffness of railroad bed and settlement of soft ground induced by trapped or seepage water lead to problems in safety of train operation. In this research, characteristic stiffness of concrete tracks, which is determined from FRACTAL (Flexural-Rigidity Assessment of Concrete Tracks by Antisymmetric Lamb Waves) technique, was employed as an index of track displacement. The characteristic stiffness is defined using Poisson's ratio, moment of inertia and stiffness ratio of subgrade to slab. To verify validity and reliability of the proposed characteristic stiffness, experimental and theoretical researches were performed. Feasibility of the characteristic stiffness based on FRACTAL technique was proved at a real concrete track for Korean high-speed trains. Validity of the FRACTAL technique was also verified by comparing the results of impulse-response tests performed at the same measurement array and the results of SASW tests and DC resistivity survey performed at a shoulder nearby the track.

• Journal of the Korean Geotechnical Society
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• v.25 no.8
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• pp.95-106
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• 2009

This study was intended to identify the effect of the wetting on a long-term compression settlement of the rock/soil mixture used as fill material, depending on compaction and grading conditions. The relatively large settlement happened under the fully-submerged condition, and a repeated settlement was monitored when moisture content increased over and over again like the rainfall infiltration. In case of the materials without fine fractions or compacted in wet condition, the settlement caused by wetting was relatively low. In conclusion, the long-term compression settlement of granular (rock/soil mixture) fill material is more affected by the increase of water content and temperature change (freezing and thawing) than creep.

• Journal of the Korean Geosynthetics Society
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• v.12 no.3
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• pp.15-22
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• 2013

By changing from ballasted track to concrete slab track, new type railroad subgrade is strongly required to satisfy strict regulations for displacement limitations of concrete slab track. In this study, sensitivity analysis was performed to assess the design characteristics of new type reinforced railroad subgrade, which could minimize residual settlement after track construction and maintain its function as a permanent railway roadbed under large cyclic load. With developed design program, the safety analysis (circular slip failure, overturning, and sliding) and the evaluation of internal forces developed in structural members (wall and reinforcement) were performed according to vertical installation spacing and stiffness of short and long geotextile reinforcement. Based on this study, we could evaluate the applicabilities of 0.4 H short geogrid length with 0.4 m vertical installation spacing of geotextile as reinforcement and what the ground conditions are for the reinforced railroad subgrade. And also, we could grasp design characteristics of the reinforced railroad subgrade, such as the importance of connecting structure between wall and reinforcement, boundary conditions allowing displacement at wall ends to minimize maximum bending moment of wall.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.35 no.2
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• pp.515-524
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• 2015

The number of occurrence of differential settlement and track irregularity at track transition zone recently comes to increase, which leads to frequent maintenance activities that have an impact on train operation. Such track transition zone damages are attributed to the change of mechanical properties of fill materials due to environmental factors such as rainfall and freeze, and thaw. Consequently, this study attempts to establish the soil water characteristic curve (SWCC) of fill materials, and conduct seepage analysis to assess the distribution of degree of saturation (DOS) for track transition zone in case of rainfall. The SWCC of fill materials was successfully obtained using filter paper test method. The results of seepage analysis revealed that rainfall intensity, the slope of backfill, backfill condition (fill or cut), and SWCC are significantly influential in controlling the distribution of DOS.

• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1279-1286
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• 2006

It is very important to pay careful attention to construction of earthwork/tunnel transition zone for railway. The transition zone of the railway is the section which roadbed stiffness is suddenly varied. Differences in stiffness have dynamic effects and these increase the forces in the track and the extent of deformation. In this study, performance of transition zone was investigated through the field tests. The wheel loads and sleeper settlement were measured after installing field testing sections.