Track Monitoring
Taiwan: Taiwan is building a high-speed railway between its two largest cities, the northern city of Taipei and the southern city of Kaohsiung, some 345 km away. The HSR will cut inter-city travel time to just ninety minutes, down from 4.5 hours with the existing rail system.
To provide a level and unobstructed route for the HSR, Taiwan is constructing 62 km of tunnels and nearly 250 km of viaducts and bridges. The viaduct at left is typical. Its piers are tall enough to carry it above above existing railways or highways.
At the site discussed in this story, piers for the viaduct were to be located on both sides of a busy railway. To verify that the track bed remained safe, stable, and operational during excavation of the foundation for the piers, a track monitoring system was required. The Taiwan Railway Administration required that the automated system obtain data at 30 second intervals and transmit the data to a remote base station for analysis. The contractor required that the system be self-powered, competitively priced, and supported by good service.
The Track Monitoring System
San Lien Technology Corporation proposed a system of horizontal EL beam sensors to span the excavation area on either side of the tracks, as shown in the drawing. The linked sensors were tied to a benchmark so that each sensor would report settlements relative to that benchmark. Because the sensors have a low profile, it was possible to mount them directly on the sleepers using expansion anchors. Rubber washers were used to prevent loosening of nuts and bolts during the intense vibration caused by passing trains. The photo below shows a string of beam sensors. The beam perpendicular to the track is fixed to a benchmark.
A Campbell Scientific CR10X data logger was used to read the sensors. The CR10 system consisted of the logger itself, a 12V power supply charged by a solar panel, a multiplexer to allow connection of the beam sensors, and a Wavecom GSM 900/1800 modem for wireless transmission of data. Communications were controlled by Campbell Scientific PC208W software.
Installation of the instrumentation went smoothly, but the installation team had to be very alert to train movement and keep everyone at the site informed of their work. In erecting the solar panel, the team had to pay special attention to the high-voltage overhead power cable used by the railway.
Comparison of Track Monitoring Methods
In the past, railways had only two options for monitoring track safety: visual inspections and leveling surveys. Now, there are other options: high-tech instrumentation coupled with data loggers and wireless data transmission. The table below shows a comparison of the two methods.
| Factor | Traditional Method | Automated Method |
|---|---|---|
| Time and Manpower | Requires more time and manpower. Every inspection requires at least one person. Leveling surveys require equipment and more than one person. | Requires very little time and manpower. Most inspections are done by instrument. |
| Monitoring Frequency | Monitoring frequency is low, limited by availability and expense of manpower. | Monitoring frequency is continuous. |
| Affected by Weather | Weather conditions can affect accuracy and reliability of inspection. | Weather conditions have no effect on automatic monitoring. |
| Safety | Safety is lower in two respects. An inspector must walk the tracks, so safety for the inspector safety is lower. Safety is also lower for the rail system, since inspections are less frequent. | Safety is higher in two respects: There is no human exposure to danger. Safety for the railway is higher, since inspections are nearly continuous. |
| Cost | Higher expenses in the long term. | Higher expenses in the short term. |
Conclusion
Taiwan has many large rail projects already underway or in planning, including MRT systems in Taipei and Kaohsiung, additional sites of the High Speed Rail project, the Taiwan Eastern Railway Improvement Project, the Metropolitan MRT and Rail Transportation Project and the C.K.S Airport Rail Link Project.
These projects, all being built in densely populated and developed areas, will require safety monitoring and are likely to benefit from automated monitoring such as the system described above.
Thanks to Mu-Pin Kao of San Lien Technology Corporation for contributing this story. San Lien is the exclusive representative in Taiwan for Slope Indicator products.