Rail Track Monitoring – Minneapolis Light Rail Transit System Extension
Challenge
As part of the $2.75 Billion Minneapolis Light Rail Transit System 14.5 mile extension project, a 30-40 ft deep excavation of a 3/4-mile long tunnel was performed directly adjacent to active track. As such, it was necessary to monitor the track for any movement resulting from the excavation to help ensure the adjacent freight rail line remained operational and safe.
Additionally, the weather conditions in Minnesota added challenges for other wired monitoring systems previously utilized. Specifically, the Terracon team first tried using a MEMS tiltmeter wired monitoring system; however, even with protective supports around the system, it was highly sensitive to physical damage and failure from moisture intrusion, and its high profile made it susceptible to damage from trains or track maintenance equipment. The system often required removal and replacement for track maintenance. The cost of the sensors also meant that compromises were made in terms of the number deployed.
The team also deployed Automated Motorized Total Stations (AMTS) to determine track movement but this didn’t work reliably due to the requirement for line of sight between the AMTS and the target/ prisms which were often covered with snow during winter, causing loss of data and excessive system maintenance. High AMTS power consumption was also a factor.
Solution
As an initial trial, the Terracon team monitored 100 feet of track using Senceive Nano Triaxial Tilt Sensor Nodes and FlatMesh Gateways because this solution was both waterproof and wireless.
What was measured:
- Crosslevel displacement in Inches
- Track “twist” in inches
- Estimated settlement profile as supplemental
- information
Outcome
Direct measurements of tilt and twist could be recorded every 5 minutes at every 10 feet so adherence to the published FRA threshold limits for both of these movements could be easily determined. Automated alert warnings were set up to be triggered if movement exceeded pre-set threshold values.
The Terracon team was able to quickly install the Senceive system. After the success of the trial, Terracon and the owners expanded the monitoring program to the full-scale project.
A total of 180 FlatMesh™ NanoMacro High-G track tilt sensors were installed every 10 feet along the track to measure changes in twist and crosslevel displacements. Three cellular gateways with internal batteries and small 20-watt solar panels were installed to ensure continuous data collection.
Reporting frequencies could be changed remotely from the online WebMonitor™ portal as required.
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Created on: Tue 29th Aug 2023
“Some of the big advantages we saw to [Senceive’s] system were we now had sensors installed every 10 feet along the freight track, we couldn’t reasonably do that with any of our previous monitoring systems. Another huge advantage, especially compared to our AMTS, was that we’re getting a reading every 5 minutes even if the sensors are buried in snow or a train is passing, we are always getting our readings because we don’t have to rely on line of sight. A huge plus is that it is completely wireless, anyone who has worked with wired systems know they are a huge hassle.”
“I find the spatial view on [Senceive’s WebMonitor data visualization platform] most useful and all of the people who need access to it, have it …it is easy to understand and
everything goes smoothly.”
“The biggest thing is that the project owner and railroad are really happy and comfortable with the type of information we’re able to provide to make sure that the track is safe for trains to pass.”
