Automating tunnel as-built surveys for Grand Paris Express

Tunneling on a grand scale in Paris

The Grand Paris initiative, launched in 2007, aims to maintain Paris’s global competitiveness while preserving its history and heritage. By incorporating three neighboring districts, Hauts-de-Seine, Seine-Saint-Denis and Val-de-Marne, the metropolis expanded from 2.2 million to more than 12 million inhabitants.

To support this population growth, the Grand Paris Express project is constructing the largest urban rail expansion in the Western Hemisphere. Valued at more than $35 billion, the project will expand the regional transit network by adding 200 kilometers (124 miles) of new lines and 68 new stations in a ring route around Paris. The goal is to serve two million additional daily riders by 2030.

With 90% of the new lines located underground, tunneling presents significant risks to schedules and budgets. Leading French civil construction firms Eiffage Génie Civil (Eiffage GC) and Razel-Bec formed joint ventures to handle major subterranean segments, including Line 15 and the extension of Line 14 South. To minimize risk and ensure project timelines are met, the teams partnered with Trimble to adopt automated surveying and monitoring technologies.

Implementing real-time monitoring and automated surveying

On the L15B tunnel section near Champigny Centre, construction required excavation near homes, businesses and utilities. Eiffage GC and Razel-Bec installed a Trimble 4D Control (T4D) monitoring system featuring 25 Trimble S7 robotic total stations and Settop M1 wireless communication hubs. The setup allows remote operation and live video feeds while automatically storing data and running network adjustments, ensuring uninterrupted measurement even if internet connectivity drops. Mounting total stations on nearby building facades was facilitated by the silent operation of the Trimble S7 magnetic drive, preventing noise disruption to local residents.

For the Line 14 South tunnel — an upgrade connecting Paris to Orly Airport — tunnel boring machines (TBMs) were deployed alongside precise as-built surveys. Survey engineer Olivier Gauche utilized the Tunnel Module in Trimble Access software paired with a Trimble S7 total station and Trimble TSC7 controller. The system performed rapid automated profile measurements of the concrete tunnel rings, shooting 20 to 30 profiles at 1-meter stations along the alignment at rates up to 15 points per second. Underbreak and overbreak analysis routines provided immediate feedback on-site to verify proper placement of the tunnel lining.

Additionally, teams deployed the Trimble SX10 scanning total station to capture georeferenced point cloud data for tunnel walls, ceilings and floors, as well as to verify ring convergence. Data captured in the field was seamlessly processed using Trimble Business Center (TBC) office software for traverse computations, template creation and point cloud comparison to the design model.

Streamlining construction while protecting surrounding assets

The automated surveying and monitoring solutions deployed by Eiffage GC and Razel-Bec yielded significantly improved project timelines and richer datasets compared to legacy workflows. Automated monitoring provided real-time movement detection, allowing crews to safeguard adjacent surface structures and underground utilities against potential ground settlement or bow-wave perturbations caused by TBM excavation.

In the tunnel, automated ring profiling drastically cut field and office processing times. Instant underbreak and overbreak reporting provided TBM operators with real-time feedback to maintain alignment with design specifications, preventing costly rework during the finishing phase. Following their success on Line 15B and Line 14 South, Eiffage GC and Razel-Bec plan to deploy these connected Trimble workflows across additional Grand Paris Express sites.