Architecture and management of a geological repository - Andra

7 – The shafts and the drifts• Upper retaining plugA concreted containment plug covers the core. It is anchored in the rock, on which it relies to resist thepush by the swelling clay. Its effectiveness is therefore independent from the state of the shaft liner.The geometry of this plug is two opposing cone frustums at 35°, so that it works by compression andthus has no need of reinforcements.Figure 7.7.9Containment plug for a shaft seal7.7.3.3 Construction techniquesAll equipment is removed from the shaft before it is closed. The closing operations use equipmentsimilar to that used for sinking.For the construction of the clay cores, the liner is removed and the clay installed are the same time:several successive passes take place, to limit the unsupported height and ensure site safety. The liner isremoved therefore in two metre-high sections approximately. The shaft wall may be surfaced using asmall road header machine. Wire mesh and steel arches are installed if needed to support theuncovered facing. The swelling clay is then set in place over the height of the section, by graduallyraising the temporary ground support structureA variant has been studied to take into account uncertainties over the long-term behaviour of theargillite with respect to the mechanical stability of the shaft wall. This consists of leavingmechanically-reinforced liner rings in place. The shaft wall is therefore only exposed in 7-metresections approximately, separated by 3.5 m-long rings. The ring reinforcement consists of radial,concrete anchoring studs in the argillite.The concrete is simply poured in place to construct the containment plugs.Lastly, backfill may be used for traditional compacting, in horizontal layers a few tens of metres thick.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM319/495