Detection of railway ballast damage under a concrete sleeper based on impact hammer test

This paper focuses on the detection of ballast damage under a concrete sleeper based on the vibration measurement of the in-situ sleeper. The rail-sleeper-ballast system is modeled as a Timoshenko beam on an elastic foundation. Ballast damage reduces the ballast stiffness in supporting the sleeper. This paper reports the modeling of the rail-sleeper-ballast system and the Bayesian model updating of the ballast stiffness distribution under the sleeper utilizing the measured vibration data from an impact hammer test. The accuracy of the identified ballast stiffness distribution depends very much on the level of modeling error and measurement noise. In the proposed method, the Bayesian probabilistic approach is adopted to explicitly address the uncertainties associated with the model updating results. In order to study the feasibility of the proposed method, a segment of a full-scale ballasted track was built and tested under laboratory conditions. The experimental case study results are very encouraging showing that it is possible to apply the proposed method to detect the "region" of ballast damage and estimate the percentage reduction in stiffness. A discussion on the difficulties to be overcome before this approach can be put in real applications is given at the end of this paper.