Architecture and management of a geological repository - Andra

10.3.5 Industrial experience feedback concerning monitoringObservation and surveillance are now a standard practice in many fields of activity such as major civilengineering projects, nuclear power stations and the mining and oil industries.Repository structures are analogous to certain types of civil engineering structures, which alreadybenefit from feedback of monitoring experience. The instrumentation of shafts, drifts and type B wastedisposal cells benefits principally from feedback from experience gained in the construction of rail androad tunnels and that from concrete structures such as concrete hydraulic dams or the containmentenvelopes in nuclear power stations. For type C waste or spent fuel disposal cells, the feedback used isthat from the instrumentation of pipelines, pipework networks and bearing piles. The monitoring ofclay-cored barrages and clay repository covers and experimental data concerning seals and back-fillingin underground laboratories, provide lessons concerning the monitoring of clay components (seals,back-fill and swelling clay buffers where applicable) within a repository.10.3.5.1 Experience feedback from the monitoring of major civil engineering structuresFeedback from observation and surveillance demonstrates the benefits to be gained from monitoringduring both the construction[95]and operational phases within installations 144 . It enables knowledge tobe gained of how to design, build and operate a monitoring system [96], [97]. Finally, it has beenpossible to trial and test equipment under various environmental conditions and over periods of up toseveral decades.In the field of tunnelling, monitoring has been a standard procedure for 10 to 20 years, both in oldtunnels for maintenance purposes and in the design of new structures. This feedback can be ofconsiderable interest in repositories given their similarity to such structures.Monitoring combined with numerical modelling is a diagnostic tool for assessing the condition of oldtunnels. It makes it possible to define the actions required to strengthen them or bring them up tocurrent standards. As an example, this approach is used by “Réseau Ferré de France” for maintainingnumerous rail tunnels, some over a hundred years old, that are still in service [98].For more recent tunnels, monitoring has been gradually introduced, due to environmental constraintsimposed on urban sites (excavation beneath existing constructions, often in loose soil) and in order toimprove or optimise the designs of the structures. In both cases, it enables terrain deformation to bemonitored and to adapt the excavation and support procedures where necessary. This was the case, forexample, for the construction of the structures for the EOLE (and METEOR) railways under Paris andfor the Tartaiguille tunnel, one of the largest underground structures for the French Mediterraneanhigh-speed train (TGV) link, for crossing an area of marl. In the case of the Chamoise motorwaytunnel, consisting of two independent tunnels commissioned ten years apart (in 1986 and 1996),instrumentation and monitoring of the first structure after its construction enabled the design of theslab of the second tunnel to be improved. Moreover, the monitoring of the behaviour and condition ofsuch structures during their operation makes it possible to detect maintenance requirements at an earlystage.In the nuclear field, the monitoring of the pre-stressed concrete containment envelopes of nuclearpower stations was designed into the construction of the first power station (first section of theFessenheim reactor in 1971). The monitoring adopted mainly concerns the operating safety of thenuclear installation. But it also enables knowledge to be gained of the physical condition of theconcrete during the structure’s lifetime. The data thus acquired can then contribute to the decisionmakingprocess concerning the management of the power station, for example an extension of itsoperational life.144 A few decades ago, the monitoring of a structure was still often considered as a financial and technical burden which produced littlebenefit in return.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM392/495