Architecture and management of a geological repository - Andra

5 – Repository Modules5.1.3.2 Detailed description of the cell in operating configuration• Description of the useful part of the cellThe useful part of the cell is a drift with an excavated diameter of 10 to 12 m. The form of theexcavation is quasi-circular or horseshoe-shaped, in order to best fit the different package dimensions,so as to minimize the volumes excavated and the volumes of concrete, while only stressing the liningconcrete in compression. To extend the maximum lifespan of the cell structure, the amounts of steelare reduced to the minimum to avoid possible corrosion.Figure 5.1.12 illustrates the various components of the useful part of the cell.Figure 5.1.12Main section of a B cellThe cell’s ground support is designed to ensure worksite safety while minimizing long-termdisturbances. To minimize disturbance in the argillite and restrict the introduction of metalcomponents into the cell as much as possible, the ground support consists of short steel rockbolts,2.40 m in length, which do not therefore exceed the extent of the microfissured clay zone 66 . A steelwelded mesh and B40 67 glass fibre reinforced shotcrete, 25 cm thick, complete the device. Thissolution was preferred over more conventional solutions such as metal arches or 5 m long bolts, whichwould have penetrated much farther into the rock and possibly enlarged the damaged argillite zone atthe walls. In the event standard equipment is used, the diameter of the cell makes it necessary toexcavate and support the section of the cell in two phases. Owing to ground support installationconstraints, the drift side walls must be widened at mid-height. The use of specific equipment wouldmake it possible to excavate and support the cell in the middle of the section and would prevent these"elephant’s feet" from forming.The lining and the filler concrete, although having different functions, are cast as a single assembly forreasons of construction. The lining (with structural slab) is only subjected to compressive stress and isnot reinforced (Figure 5.1.13). Preliminary dimensioning gives this structural ring a thickness ofapproximately 70 cm for a B60 concrete. The filler concrete forms the boundary of the rectangulardisposal chamber. Dry joints 68 are used in the filler concrete so as not to interfere with the stresses inthe structural ring. Stainless steel hangers locally reinforce the filler concrete.666768Composite glass fibre - resin rods could be used as a variant, and/or a resin seal.Concrete whose simple compressive strength is 40 MPaGrooves made in the concrete and left emptyDOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM173/495