Detection of Hidden Defects on Railway Sleeper and the Underlying Ballast Utilizing Impact Hammer Test of the In-situ Sleeper

Description

The ballasted track system is one of the most important railway transportation systems. Given the importance of railway safety, research work with industrial applications has been carried out. The current railway track monitoring system is comprehensive. Fast and efficient methods are available for monitoring of railway level and alignment, rail gauges, corrugation, etc. However, the monitoring of the functional condition of railway sleepers together with the underlying ballast still heavily relies on visual inspection. It is clear that visual inspection is good in detecting “surface” damage. For hidden defects, such as cracks at the bottom of the concrete sleeper and the ballast defects under the sleeper loading area and/or ballast shoulder, which can affect track stability and deteriorate riding quality, are extremely difficult, if not impossible, to be detected through visual inspection. In a ballasted track, the ballast keeps the sleeper in position, and the sleeper supports the rails. If there is any damage to the sleeper and/or ballast, the stiffness of the rail-sleeper-ballast system will be reduced. This will alter the dynamic characteristics of the system, and this change can be reflected from the measured vibration data of the in-situ sleeper. The idea of damage detection by monitoring the vibration of the target system is not new. There are studies from the literature about the use of vibration data of the in-situ sleeper in quantifying the stiffness of either the sleeper or the ballast. With the advance in modal testing techniques, it is not difficult to measure the changes in dynamic characteristics (e.g., natural frequencies and mode shapes) with high accuracy. However, the changes can be induced by sleeper damage and/or ballast defect, and there is no existing method that can be used to classify the types of defects without lifting up the sleeper. This is the largest obstruction in the application of vibration-based damage detection methods to the health monitoring of ballasted tracks. One of the main objectives of the proposed project is to overcome this difficulty and develop a practical method to provide valuable information about the “health” status of each concrete sleeper and the underlying ballast to engineers and inspectors during visual inspection.