The Effect of Traffic on Ballast Settlement

Abstract

The main factor that contributes to the deterioration of track components is traffic load. Explanations on how the speed, load and repetition of traffic in-fluence the long-term settlement of ballast in a ballasted track are very scarce. Having in mind that tracks subjected to the same load show different settle-ment behavior, explanations of track settlements in accordance with the speed, load and repetition are needed. This study is motivated to show how traffic affects the long-term settlement of ballast and how the traffic parame-ters (speed, load and repetition) contribute to the process. Using finite ele-ment modeling software, the three-dimensional track is modeled and ana-lyzed for different values of speed, load and number of repetitions. Drucker Prager plastic model is applied for the ballast and sub-ballast materials of the track. To get the parameters for the Drucker Prager plastic model of granular materials, triaxial test simulation is performed using discrete element soft-ware. Hertz’s contact theory is used to model the contact between the wheel and rail. The long-term settlement behavior of ballast material is analyzed by applying 8000 cycles of moving axel load. According to the analyses, a change in the speed and the number of repetitions of train movement changes the permanent settlement of ballast more than the variation in load. Increase in the speed of train movement by 20 km/hr. will increase the stress transferred to the subgrade by up to about 1000 kPa. Speed of train movement is the most contributing parameter in the degradation of ballast material more than the load and number of repetitions. In a conventional ballasted track after about 6000 repetitions of train movement ballast material will start to de-crease its performance. The comparison of the effects of the variation of indi-vidual traffic parameters speed, load and number of repetitions on the settle-ment of ballast which is not touched by former researches is well addressed by this study which is very helpful for designing a new railway track and monitoring existing railway tracks. Based on the analysis of the model with the parameters from Ethio-Djibouti standard gauge railway track, the possi-ble maintenance period of ballast material is predicted.