Description:
This bridge had identified issues with approach embankment settlement. Soft embankments and hard transitions in stiffness between approach and bridge structure can pose a risk to trains and the bridge due to sudden geometry changes in the rail.
EngAnalysis were engaged to develop a monitoring solution that could measure and quantify the amount of rail displacement under dynamic, fast-moving trains. Some challenges in doing this include:
- System must operate remotely in harsh rail environment
- System must operate and relatively high speed to capture dynamic effects
- System must be accurate to less than 1mm
- System must be installed in short shutdown window
The speed and accuracy requirements ruled out several traditional displacement monitoring methods and EngAnalysis proposed to develop and trial a unique system.
We installed remote PTZ cameras outside of the rail exclusion zone. The cameras are wired to a cabinet where data is transmitted via an LTE modem to the EngAnalysis data center. The cameras, computer and modem are powered by a solar system including panel and battery. Video recording is triggered by a train detection sensor which enables high speed video recording and transmission during train passes. The cameras can also be logged onto remotely at any time for static, manual monitoring.
There are 30 IR targets installed on the rail, sleepers and bridge. Core to the monitoring success has been the software and digital image analysis techniques developed by our team. Our custom-built software measures changes in pixel intensity on the targets and incorporates a weighted centroid to achieve sub-pixel resolution. We are then able to monitor changes in displacement at the frame rate of the camera and can achieve 1mm accuracy.
This is a cutting-edge monitoring application and the results delivered have provided valuable insights to our customer. We observed a gradual loss of stiffness of the approach with increasing dynamic displacement behind the bridge abutment. We were able to then develop a trend for the loss of stiffness and make predictions for when thresholds would be reached. Further, our system detected the results of a re-tamping operation, showing that the re-tamp was highly effective in restoring stiffness behind the abutment.
With this system, our client is able to remotely monitor the situation, plan maintenance work and verify the effectiveness of that work, resulting in significant risk reduction, increase in safety and allowing our client to focus their resources on other problems.