Architecture and management of a geological repository - Andra

7 – The shafts and the drifts- In the Callovo-Oxfordian layer, two types of ground supports are planned. In the future shaftsealing zone (see below in section 7.7.3), steelsets arches and shotcrete will be used; this zoneextends fifty metres above the top of the formation. Outside of the sealing zone, the groundsupport consists of 4 m long rockbolts and shotcrete.At the current stage in the studies, the concrete liner thickness is 45 to 50 cm in the earths locatedabove the Callovo-Oxfordian layer and 1.35 m in the Callovo-Oxfordian layer, except for the localreinforcement at the shaft station.The ground support and shaft liner were sized using conventional geotechnique analytical methods(″convergence confinement method″ 117 , associated with a ″beam element calculation″ 118 in order totake into account the anisotropy of the horizontal stresses). The sizing parameter is the pressureapplied by the surrounding ground and, in particular, the pressure exerted by the argillite because of itscreep. Studies show that the chemical degradation phenomena of the liners only take place over verysignificantly longer durations. This ensures a multiple 100-year service life for the structure.The ground support and the liner of the other shafts are similar and adapted according to the shafts’respective diameters.The distance between the shaft bottom and the wall of the Callovo-Oxfordian formation isapproximately thirty metres based on the assumption of a 130 metre thick formation.117 The convergence confinement method uses the stress – deformation curves of the liner (or the ground support) and the ground. Theequilibrium of the liner – ground system is located at the intersection of these two curves.118 In the beam element calculation, the liner is schematically represented by a set of beam elements and the ground’s action isschematically represented by springs. This calculation combined with the convergence – confinement method allows processing thecases of anisotropic stresses.DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM293/495