Measurement of rail deflection on soft subgrades using DIC

The measurement of track displacement during the passage of a train is an important parameter for the assessment of track condition. Digital image correlation (DIC) is a non-contact camera-based technology that can be used to measure these displacements. However, ground vibrations induced by the train can result in camera movement, adding error to the measured displacement. This paper presents a two-camera method that can account for the camera movement when measuring track displacements using DIC. The method is validated on a stationary track and then used to measure track displacement during the passage of two trains travelling at different velocities. The results of the two-camera method are then compared to the track displacements found using a low-pass filter. The two-camera method was found successfully to reduce error due to camera movement while removing the subjectivity of choosing a cut-off frequency for filtering.