Continuous Tunnel Convergence Monitoring at Andra

Andra, France’s national radioactive waste management agency, is developing Cigéo, a deep geological repository located 500 metres below ground in north-east France. The project aims to provide a long-term, safe solution for radioactive waste storage, requiring unprecedented levels of structural stability, monitoring reliability, and operational safety.

Within Andra’s Underground Research Laboratory in Bure, extensive testing is carried out to understand how rock masses behave after excavation. One key phenomenon is tunnel convergence: the gradual deformation of surrounding rock, causing galleries to slowly close and apply stress to structural linings. While convergence is most rapid in the first months after excavation, it continues at a slower rate over time making long-term observation essential.

To support this work, Andra partnered with Fugro and its subcontractor FRO to evaluate automated monitoring methods capable of delivering continuous displacement data with minimal human intervention.

The Challenge

Traditionally, tunnel convergence at the site has been measured using manual invar wire techniques and periodic geodetic surveys. While proven, these methods require skilled personnel to enter confined underground spaces and provide only snapshot measurements every few weeks.

For future storage galleries, Andra identified several limitations with this approach:

• Manual measurements introduce operational risk and human error

• Periodic surveys miss short-term deformation trends

• Increasing restrictions on underground access will limit future inspection capability

• Existing geotechnical sensors lacked the spatial resolution needed to assess structural behaviour

Andra required a remote, autonomous system capable of delivering continuous, high-precision convergence data while operating reliably in harsh underground conditions with ongoing drilling activity.

TotaLite was deployed as part of a six-month pilot programme to evaluate automated optical monitoring in newly excavated tunnel sections.

Installed in January 2024, the compact image-based sensor captured displacement data every five minutes, measuring both vertical and horizontal movement across multiple cross-sections. Standard survey prisms were mounted inside the tunnel, enabling sub-millimetre tracking of structural response.

Key system characteristics included:

• Continuous 2D displacement monitoring

• Sub-millimetre accuracy

• Compact form factor suited for confined spaces

• Autonomous operation with minimal maintenance

• Near real-time data transmission to Andra’s Data Acquisition and Management System (SAGD)

• Cloud-based visualisation with configurable alerts

Measurements were compared against Andra’s established manual wire readings taken approximately every two weeks.

Despite occasional disturbances to prisms caused by personnel and equipment in the narrow tunnel environment, TotaLite demonstrated strong alignment with traditional convergence trends, capturing the same gradual tunnel closure and progression toward equilibrium — while providing significantly higher temporal resolution.

Results

The pilot confirmed that TotaLite could reliably operate in demanding underground conditions while delivering continuous deformation insights not achievable through periodic methods alone.

Key outcomes included:

• Validation of displacement accuracy against established manual techniques

• Continuous visibility into tunnel behaviour during early convergence phases

• Reduced need for personnel access to underground galleries

• Elimination of manual data handling errors

• Real-time monitoring capability supporting faster safety assessment

Following the study, Andra approved the system for permanent installation to monitor roof deflection inside the Westfalenhallen structure, marking a transition from pilot testing to operational deployment.

By providing remote, autonomous monitoring, TotaLite enables Andra to reduce human exposure, improve structural insight, and prepare for a future where underground access will be increasingly restricted, supporting safer, data-driven decisions for long-term nuclear waste storage.

Betrand Chalazy

Fugro Chief Surveyor

"Having tested TotaLite A1.0 for tunnel monitoring and other monitoring work on a number of projects, we are amazed at what it does.  Given its size and accuracy it can be used where an automated total station can not."