Investigating the Mechanical Behaviour of Railway Ballast
thesis
posted on 2017-01-05, 03:25 authored by Osama Saud M BrinjiThis thesis
aims to gain further understanding of the mechanical behaviour of a railway’s
ballast. Ballast is considered to be the stone bed located under the railway
track. There are currently three major types of material used for sleepers:
timber, concrete, and steel. Concrete sleepers are most commonly seen in the
railway industry, however for freight transportation by rail, steel sleepers
are being increasingly used. This is due to their durability, ease of
installation, and maintenance, particularly in harsh environmental conditions.
However, the existing design of steel sleepers has not been improved to account
for the increase in load of the freight trains over the years. Furthermore,
more complications and disturbances arise in curved segments of railway tracks.
Hence this research focuses on determining how the steel sleepers are affected,
and methods for improving their response under load.
Three distinct experiments were conducted as part of this study. The first experiment determined the mechanical and dynamic response of the ballast with a sleeper in laboratory environments. The second experiment was a field experiment conducted in Whyalla, South Australia, which investigated the behaviour of the ballast and steel sleeper in both tangent and curved track. The final experimental study involved determining the effects of changing various geometric parameters of the existing steel sleeper design and subjecting it to either horizontal or vertical loads.
The initial experimental study found that the experimental apparatus used to measure data agreed well with the current literature. Additionally, it was found that no studies have determined the effect of ballast sizing on interaction behaviour. From the results gathered as part of this research, it was confirmed that ballast sizing does not affect the sleeper and ballast interaction. It was also important to determine the natural frequencies of the ballast, as it was found to either reduce or amplify the interaction between the two systems. The field experiment was a vital part of this research, as it gathered critical data on existing systems. The research found that the vibration between the ballast and the steel sleeper was significantly higher in a curved track compared to a tangent track. Additionally, a low strain was measured in both the curved and tangent track, indicating that the amplification factor used in the design calculation in the Australian Standard is sufficient. The final parametric study showed that increasing the thickness and depth of the steel sleepers does not affect the response of the system. In contrast, in some cases, it may even worsen the vibration interaction between the sleeper and the ballast.
Overall, through this research, it has been found that the current experimental setup in laboratory environments agrees well with the field results. However, in order to improve the interaction between the steel sleeper and ballast, further design changes need to be looked into, particularly for curved sections of a track, have been shown to be more critical than tangent tracks. Modifying the ends of the steel sleeper (spade) will provide further insight into achieving better interactions between the ballast and the sleeper system.
Three distinct experiments were conducted as part of this study. The first experiment determined the mechanical and dynamic response of the ballast with a sleeper in laboratory environments. The second experiment was a field experiment conducted in Whyalla, South Australia, which investigated the behaviour of the ballast and steel sleeper in both tangent and curved track. The final experimental study involved determining the effects of changing various geometric parameters of the existing steel sleeper design and subjecting it to either horizontal or vertical loads.
The initial experimental study found that the experimental apparatus used to measure data agreed well with the current literature. Additionally, it was found that no studies have determined the effect of ballast sizing on interaction behaviour. From the results gathered as part of this research, it was confirmed that ballast sizing does not affect the sleeper and ballast interaction. It was also important to determine the natural frequencies of the ballast, as it was found to either reduce or amplify the interaction between the two systems. The field experiment was a vital part of this research, as it gathered critical data on existing systems. The research found that the vibration between the ballast and the steel sleeper was significantly higher in a curved track compared to a tangent track. Additionally, a low strain was measured in both the curved and tangent track, indicating that the amplification factor used in the design calculation in the Australian Standard is sufficient. The final parametric study showed that increasing the thickness and depth of the steel sleepers does not affect the response of the system. In contrast, in some cases, it may even worsen the vibration interaction between the sleeper and the ballast.
Overall, through this research, it has been found that the current experimental setup in laboratory environments agrees well with the field results. However, in order to improve the interaction between the steel sleeper and ballast, further design changes need to be looked into, particularly for curved sections of a track, have been shown to be more critical than tangent tracks. Modifying the ends of the steel sleeper (spade) will provide further insight into achieving better interactions between the ballast and the sleeper system.
