The Smart Monitoring Solution for the Rennes Metro

Author: Guillaume Labrie, Clément Anet (Datageo), Steve Thurgood, Ruth Badley

When surveying and geometric engineering specialists DataGeo and Kadran Ingenierie needed to provide continuous monitoring during an extensive rail line expansion in Rennes, France, they consulted with Leica Geosystems to find a solution that would meet the technical challenges of the project. Using the innovative WiSenMeshWAN® system of wireless geotechnical sensors, the solution proved effective for monitoring the Rennes rail line by simplifying data collection and the overall workflow, and also enabled DataGeo and Kadran to expand services and accept monitoring projects that were not possible before.

A large-scale extension to the light railway in Rennes is designed to make the French city an even more attractive and convenient place to live, do business and visit.

A commitment by the municipal authorities to introduce efficient and sustainable public transport systems to Brittany’s capital began in 2002 when the first fully automatic rail route (Line A) became operational. At the time Rennes was the smallest city in the world with a metro system.

The driverless trains on Line A cover a distance of 8.6km, transporting around 140,000 passengers daily. Construction of the new Line B signals the city’s ambitions to benefit more travellers by widening the scope and capacity of the metro system. A 13.4km route linking the south west to the north east of the city is estimated to attract an additional 100,000 users per day.

Surveying and geometric engineering specialists DataGeo and Kadran Ingenierie, who worked on the construction project were asked to provide continuous real-time monitoring of the effects of  vibration, strain and changes in temperature on the installed track. The work site from start to end is 2.5km in length, with the track running above ground along a straight section and a series of curves.

Measuring the changes

The metro trains of Rennes are similar to driverless trams or buses, operating on a fixed route, guided by a powered rail on a concrete path. The system is fixed into the concrete structures in sections, separated by movement joints along its length.

As part of the safe operation and maintenance of the rail line, a long-term monitoring solution would inform the operating company of any track and structural deformations caused over time by vibration from the trains and variations in temperature.

Monitoring, to check readings consistently remain below a defined threshold, would ensure the train proceeds smoothly and provide essential data to stakeholders on the impact of mechanical strain on the guide rail.

An Ideal Solution

However, unique environmental factors at the site, including adjacent metal fencing masking line of sight to the track, led the team to seek expert advice from Leica Geosystems France’s Rail and Monitoring Manager, Guillaume Labrie, about the best monitoring solution for the Rennes Metro.    Guillaume suggested WiSenMeshWAN®, an innovative system of geotechnical sensors as the ideal solution. He recognised that the relative data from the WiSen sensors met the project requirements because the 3D measurements from TPS instruments were not needed. Based on automated wireless technology, these products simplify the data collection process, integrate with existing workflows and are fully compatible with Leica Geosystems’ monitoring solutions.

Monitoring Solution for the Rennes Metro:

The monitoring system included the following components:

• 4 SmartGateways with solar panels.
• 19 1CH and 14 4CH Interface nodes, installed on the expansion joints of the concrete track and the guide rail, connected to crackmeters, strain gauges and temperature sensors.
• 24 Omni Tilt and Distance sensors used to measure rail expansion and the lateral displacement of the track slab relative to the deck.

A bespoke design divided the site into 3 separate but connected measurement areas. A meshed network of long-range wireless sensor nodes and third party vibrating wire geotechnical sensors were installed at intervals on the track. Each node in the mesh automatically measures, and transmits data to a SmartGateway. The sensors operate on the lower sub 1GHz frequency, thus avoiding the interruption to communication from other radio signals like WiFi, prevalent across Rennes’ urban areas.

SmartGateways are the command units in a wireless meshed network, receiving data from all the nodes and transmitting data and system information to the remote server via mobile network. In Rennes, measurements are taken and transmitted hourly to SmartGateways, each self-powered by small solar panels. Report intervals were set and controlled remotely, though the system could automatically update and report more frequently if alerts were triggered.

Safe and Simple

Automated technology effectively removes people from potential danger by minimising the need for continual access. In Rennes, high voltage electric cables powering the trains in the vicinity of the track pose a safety risk to personnel entering the work site. Following installation, the system is controlled remotely and is virtually maintenance-free, with battery power for each node designed to last for up to 10 years of continual use.

 Measurement data is automatically uploaded to a cloud platform and can be visualised in tables and graphs that can be securely accessed, read, shared, controlled and analysed via a web browser. Complete control of the system is simple and intuitive, allowing the user to add or remove sensors, create custom computations, or change reading intervals as required.

Additional features within the system add extra value to a monitoring project as custom alert levels can be set and automated PDF reports generated and emailed, enabling the engineering team to make informed decisions.

Benefits Within and Beyond the Project

Reflecting on the impact of the innovative monitoring system, Clément Anet, Technical Manager for DataGeo/Kadran, observed a range of benefits from setup, to workflow integration, to acquiring future projects.

“Smart use of wireless technology for monitoring has simplified our workflows, adding value to what we do. Having used this equipment and this way of working, we are looking at integrating WiSen equipment into future projects that also use traditional surveying. It gives us opportunities to take on additional work we wouldn’t normally consider. It’s given us an extra tool in the box – and so simple to use. An abundance of data, reliably delivered 24/7, in a fraction of the time we expected. We plugged it all in and it just worked,” says Anet.