Seong-Hyeok Lee

Optimal Section of Ballasted Asphalt Track Considering Design Lifetime and Economic Feasibility

Compared with ballasted track (BT), ballasted asphalt track (BAT) has been increasingly adopted in many countries due to its more greatly reduced reinforced roadbed thickness and smaller cumulative plastic deformation, and its advantages in terms of maintenance. In this respect, the authors` previous research includes analysis of BAT sections that show performance similar to that of BT sections of the present specifications; reliability verification of the analysis results through real-sized static and dynamic train-load tests were performed. Based on previous research, this paper estimates the track lifetime using the strain of the lower roadbed according to reinforced roadbed thickness; using probabilistic LCC analysis, this paper presents a BAT section that satisfies the design lifetime and that has performance similar to or higher than that of BT.

Behavior Characteristics of Ballasted Track on Asphalt Roadbed Using Real Scale Test

Ballasted track on an asphalt roadbed can be beneficial for its various effects such as (i) decreasing of roadbed thickness by dispersing train load; (ii) prevention of both strength reduction and weakening in roadbed system by preventing rainwater penetration; and (iii) reducing maintenance cost by preventing roadbed mud-pumping and frostbite. With these beneficial effects, ballasted track on asphalt roadbed has been widely used in Europe and Japan, and relevant research for applying such ballasted track on asphalt roadbed systems in Korea is ongoing. In this study, full-scale static and dynamic train load tests were performed to compare the performance of ballasted track on asphalt roadbed and ballasted track. The optimum thickness levels of asphalt and reinforced roadbeds, corresponding to the design criteria for reinforced roadbed of high-speed railway, was estimated using the FEM program ABAQUS. Test results show that the earth pressure on reinforced roadbed of ballasted track on the asphalt roadbed was relatively low compared with that of simple ballasted track. The elastic and plastic displacements of simple ballasted track on the asphalt roadbed were also lower than those of ballasted track. These test results may indicate that the use of ballasted track on asphalt roadbed is an advantageous system in view of long-term maintenance.

Prediction of Cumulative Plastic Displacement in the Concrete Track Roadbed Caused by Cyclic Loading

Plastic deformation of roadbed influences the stability and maintenance of concrete slab track. Long-term plastic deformation in a railway roadbed is generated primarily due to accumulated inelastic strains caused by repeated passing of trains. Prediction of cumulative plastic deformation is important in cost-effective maintenance of railway tracks as well as for the safe operation of trains. In this study, the vertical displacements in railway roadbeds with different thicknesses of reinforced roadbed were computed. Parameters of the power model for cumulative plastic strain were calibrated by using the data from triaxial tests and full-scale loading tests. Results of three-dimensional finite element analyses of standard roadbed sections provide us with design guidelines for the selection of the thickness of reinforced roadbed.

Application of a Simple Non Destructive Test Method to Obtain the Dynamic Modulus of Asphalt Mixtures used for an Asphalt Trackbed Foundation

An asphalt trackbed is to be adapted in Korea to provide better bearing capacity and stability to the track and a comfortable ride to passengers. The dynamic modulus of Hot Mixed Asphalt(HMA) mixes is a critical design input parameter to determine the thickness of the asphalt trackbed. In this study, impact resonant tests and ultrasonic test methods are designed to obtain the dynamic modulus. These test methods are also verified to check the etffectiveness of constructing a master curve of the dynamic modulus over a wide range of frequencies and temperatures. The test results are compared to the computed dynamic modulus using AASHTO 2002 and the KPRP`s proposed model. It can be concluded that the proposed simple test methods are effective to obtain the dynamic moduli of the asphalt mixes for the design of an asphalt trackbed foundation.

Investigation of Asphalt Track Behavior Under Cyclic Loading: Full-Scale Testing and Numerical Simulation

In this study, the full-scale testing of asphalt track and numerical simulation using the viscoelastic material property of asphalt mixtures under cyclic loading was investigated. Dynamic modulus tests were conducted to characterize the linear viscoelastic property of asphalt mixtures. The full-scale test was performed to simulate train movement on the rail track with cyclic loading using the rail load simulator. The full-scale test and numerical simulations were implemented on three different layers of the asphalt with different thicknesses. The results were then subsequently compared to prove the reliability of the methods. The laboratory testing results indicate that the asphalt mixture for the surface layer, a polymer-modified asphalt, provides a high elastic modulus and behaves more elastically at low-frequency loading compared to the conventional mixtures for the intermediate and base layers. The full-scale test indicates that all cases of asphalt layer thickness satisfy the settlement criteria. However, only the asphalt layer with a 35-cm thickness attains the earth pressure requirement. The numerical simulation results are reasonable and reliable by fitting the measurement curves of cyclic loading test.

Passenger Protection Performance of Breakaway Type Posts Made of High Anti-Corrosion Steel Materials

A finite element simulation study was performed to gain an insight about the crash test details. Accuracy of the simulation was verified using qualitative and quantitative comparisons. Based on in-depth examination of crash simulation recordings, energy distributions occurred in the breakaway type posts against the car are determined. The numerical results for various parameters are verified by comparing different material models with internal energy distribution occurred in the breakaway type posts from the crash simulation.

Analytical Study of the Vibration Attenuation with respect to Trackbed Systems

The vibration-attenuation was quantitatively compared by 3-Dimensional finite element analysis using ABAQUS, with respect to the change of the type of trackbed systems. Most common trackbed materials, including ballast and concrete were applied to the track structure, and the train-speed was set as 300km/h as Korea Train eXpress (KTX). The result of current study revealed that the ballast showed the most effective material for the vibration attenuation.