The novel application of sensor technologies to monitor long-term vertical track displacement pre and post rehabilitation
Track geometry irregularities may induce travelling discomfort for passengers, vibration and noise, and critically redistribution of wheel loads causing derailments. To better understand the track deterioration mechanisms and to quantitively evaluate the success of remediation methods, a new technology is needed to enable long-term measurements of track geometry. The objectives of this thesis are to use a novel sensing technology known as a ShapeAccelArray (SAA) to measure the profile and rate of long-term vertical track displacement in real-time to a) understand the track deterioration and b) quantify the success of remediation methods. This research was conducted at a site where the section of track being monitored is known to be susceptible to long-term displacements. One SAA was installed horizontally on each side of the track to monitor the track displacement over eight months prior to rehabilitation. The SAA measurements were compared with a series of LIDAR scans taken at three different times during the SAA monitoring period to assess the accuracy of the SAA measurements. The measurements from the two systems were in good agreement and showed that the SAA can be used to measure the displacement of the track as well as the displacement rate. The rate was seasonal with slower rates of motion in dry warm summer periods and accelerated rates in wetter fall and spring seasons. The failure mechanism at the site is believed to be an asymmetrical bearing capacity failure based on the track and soil movement measured by the LIDAR scans. The section of track was then rehabilitated with rammed aggregate piers, which were installed in pairs between every other tie in the settlement zone. Digital Image Correlation (DIC) and SAAs were used to measure the instantaneous and long-term displacement of the track, respectively, in order to assess the effectiveness of the piers. It was found that the instantaneous displacements of the track were reduced at all four monitored sleepers after the pier installation. It was also found that after an initial bedding-in period of the re-ballasted and tamped construction zone, the rate of vertical track displacement decreased by an order of magnitude from the average rate of track displacement during the pre-remediation baseline monitoring, indicating the effectiveness of the installed piers at reducing long-term ground displacements.