Tome Architecture and management of a geological repository - Andra

6 – C waste repository zone• Sealing the disposal cellThe swelling clay cell plug shares the same functions as the 60-cm thick engineered barrier placedaround the packages. Additional thickness is incorporated to mitigate any mechanical confinementdefects in case of deferred settling of the backfill by swelling clay thrust. Thus a height of 1.5 m istaken as the reference.Low permeability backfill is emplaced above the swelling clay plug. It has identical proportions ofgranite aggregates and swelling clay to those used in drift backfill. The swelling clay cell plug ismechanically confined as continuity prevails throughout from the backfill at the cell head to thehandling drift. A metric thickness adopted is similar to the one considered by SKB in Sweden for itsborehole design experiments.6.4.2 Description of a handling driftThe cells are arranged along handling drifts, whose length is adapted to the geometry of the hostblock. A mean length of 250 metres may be envisaged as the reference.The standard section of a handling drift is the outcome of two dimensioning elements: cellconstruction and package handling equipment profile and the need for long term geomechanicalstability.With regard to the first point, the element used for dimensioning is the machine that transfers andemplaces the packages in the cells (cf. § 6.6.4).Just like the engineered structures described in chapter 5 for B waste and on the geomechanicalviewpoint, the geometry of the handling drifts is set in line with the granite mechanical characteristics.They are stable in the long term without the need for additional rock support other than that requiredfor operator safety (occasional ground support: shotcrete and rock bolts, etc.) Thus "inverse U"geometry is taken as the reference.This results in useful sections of 28.5-30 m 2 for a width of 5.5 m and heights of 4-4.5 m on the sidesand 5.5 m under the arch axis.Figure 6.4.3Cross-section of a handling drift during the operating phaseInterconnecting drifts, placed roughly every 150-200 m and at the ends of the handling drift, allowmachinery traffic (one-way only), rapid evacuation from an incident zone and the implementation of afresh air circuit.Dossier 2005 granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY178/228