Architecture and management of a geological repository - Andra

6 – Overall underground architecture6.3 Architectural dimensioning factorsThe dimensioning factors of repository architecture include, notably, (i) geotechnical factors that resultin constraints on the dimensions and spacing of the cells and drifts, (ii) thermal factors that also affectdistance, (iii) hydraulic factors that affect the geometric and topological layout of some architecturalelements [37].6.3.1 Geotechnical aspectsFrom the point of view of repository architecture, geotechnical dimensioning, beyond thedimensioning of the ground support and the lining of each structure (drift, cell), is a factor in thedefinition of the minimum distance between engineered structures. Given that the impact of anisolated drift on the terrain is not detected further than a distance of two diameters over the course ofseveral centuries, we have used a distance between parallel drifts or cells that is equal to at least fivetimes their diameter to ensure the mechanical independence of the structures. The stability of eachstructure on an individual basis then makes it possible to ensure the stability of the whole zone. At thispoint in the studies, account has not been taken of the effect of the "firm band" which tends to transferthe weight of overlying ground to bands of ground left untouched around edges of the excavation areasthus reducing the stress exerted on the drifts or cells.The weight of overlying terrain is transferred to the firmbands which are more rigid than the excavated areas5 diametersFirm bandExcavated areaFirm bandFigure 6.3.1Distance between structures, "firm band" effectThis minimum distance between structures applies to all cells and drifts. It is notable that in the case ofcells containing moderately or highly exothermic packages, the distance between cells is above alldetermined by thermal considerations.In the very long term, if the liners deteriorate, the limitation of residual empty space left in the disposalcells and backfilled drifts would counter the propagation of damage to the argillite [78].DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM264/495