Development of fiber optic data analysis methods for the determination of strain and damage of concrete structures

As part of the Cigéo monitoring strategy, Andra (french agency in charge of the management of radioactive waste)  is developing a monitoring system for underground structures based on a combination of complementary monitoring techniques: in situ and remote.
Fiber optic sensors will allow distributed measurements of temperature and starin. They have been referenced as a complementary means to traditional point sensors: they represent a device with great potential for measuring temperature and strain gradients along the various structures making up the underground storage. In particular, these sensors would be fixed to the steel lining of the cells intended for the storage of high-level waste, and embedded in the concrete linings of the shafts and cells intended for the storage of medium- and long-lived waste.
Fiber optics are increasingly used in civil engineering for thermomechanical monitoring of structures and for detecting potential damage. Andra is considering using Brillouin/Rayleigh distributed fiber optic sensor technology for monitoring its underground concrete structures. In its fiber optic sensor development program, Andra first sought to harden the measurement fibers and cables for use in the harsh environment of the repository and then to develop methods to decorrelate the set of useful parameters and to be able to distinguish between temperature and deformation components. The implementation of performance indicators defining the health and safety of the structure is essential, particularly in future storage decision support processes. The conversion of raw signals from fiber optic sensors into easily exploitable quantities has already been used to determine and visualize the convergence of a steel tube (A. Piccolo's thesis, 2020) for example. The algorithms and the methodological approach developed have allowed the interpretation of the observed phenomena.

To better understand the behavior of concrete structures instrumented with distributed fiber optic sensors, it is necessary to continue the work on the processing of fiber optic data applied to concrete structures. The objective is to determine the convergence of the tunnel taking into account the material data and the sensors installed in redundancy. It is also useful and necessary to define correction and adjustment algorithms to take into account the material characteristics of the concrete at young ages and the influence of long-term shrinkage/flow.

The thesis will be supervised by researchers from the Civil and Mechanical Engineering Research Institute (GeM) in Nantes. The research axes of the laboratory are based on the triptych Materials - Processes - Structures, aiming at developing and implementing integrated approaches covering the stages of design, manufacturing and operation of industrial components. The laboratory's teams are interested in the analysis of the functioning of structural components in service: response to mechanical and environmental stresses, sometimes extreme (seismic, crash), durability in the broadest sense (including risk management, life cycle analysis). The GEM is also unique in that it closely associates mechanics and opticians in the same team. Another specificity of the management team concerns the instrumentation of structures in real site conditions. We can mention the instrumentation of a port quay (IMARECO project), the instrumentation of concrete structures (ITN Infrastar project) or the supervision of Arianna Piccolo's thesis with Andra in the framework of the ITN FINESSE project.

Master in mechanic or civil engineering or physic