Project Overview

Location: France
Start:  Jan 2024
Type: Tunnel Convergence

Andra - the French national radioactive waste management agency is tasked to find environmental friendly and future proof solutions for nuclear waste. Cigéo is a project for nuclear waste disposal in a deep geological repository, 500 m below the surface in Bure, north-east France. In their Underground Research Laboratory various tests are performed prior to building the actual storage repositories. 

WHAT IS CONVERGENCE?

When digging a underground structure, the phenomenon called convergence appears: the rock deforms, tends to slowly close the structure and applies mechanical stresses to it. The design and sizing of the concrete support linings of the galleries take this phenomenon into account in particular to support it and limit the mechanical stresses applied. Work at the Underground Laboratory has shown that the evolution of convergence is rapid in the first months after the digging of a structure, then evolves very slowly.

The challenge

After construction and during lifetime, Andra wants to understand the convergence of the underground galleries ensuring stability of the tunnels. Traditional geodetic methods require skilled staff conducting manual measurements while geotechnical sensors don’t provide the required insights. The storage facilities will require remote and autonomous monitoring to minimise human intervention and provide continuous insights and alert of any undesired movements. 

Our solution

With TotaLite we provide an innovative optical solution delivering sub-millimeter accurate displacement results in an online dashboard. TotaLite was validated during a pilot of 6 months and compared against conventional methods. TotaLite captured displacement information every 5 minutes which were compared by the periodic manual wire (invar) measurements (every 2 weeks). We proved to be reliable, accurate and low-maintenance even in harsh underground conditions with ongoing drilling activities.

The TotaLite system is small - the size of a banana - and easily installed in the interior of the tunnel while requiring significantly less effort in operations than traditional geodetic instruments. A single sensor provides continuous and autonomous insights in relative displacements in both vertical and horizontal direction of multiple cross-sections providing more information than traditional (geotechnical) solutions, such as tilt meters, extensometers,  and distometers. Data is transmitted near real-time to Andra’s Data Acquisition and Management System (SAGD) and displayed in TotaLite’s online platform enabling the customer to set thresholds and receive instant alerts for unwanted movements. 

The impact

By having a remote and autonomous solution, TotaLite provides Andra and Fugro with a solution that reduces the need for people accessing the underground facilities and eliminates human-errors introduced in manual measurements. It enables experts to evaluate safety based on real-time, continuous and reliable information ensuring a future-proof solution for nuclear waste disposal.