Architecture and management of a geological repository - Andra

7 – The shafts and the driftsFigure 7.4.3Standard drift sections having an average usable diameter of 5.7 mAt the intersection of drifts of the same size, specific constructive requirements must be taken intoaccount to ensure mechanical stability. In the solution proposed at this stage in the studies, thediameter of one of the drifts is increased so that the ratio of the usable heights is approximately 1.3 inorder to give a more advantageous form to the drift intersections (the intersection of two drifts of thesame diameter would generate “flat domes”) 121 . Reinforcment pillars made of reinforced concretehaving a section of approximately 5 m 2 can also be constructed at the four corners of the driftintersection.Special arrangements can be planned for the drift sections designated to receive a seal when therepository is closed. They aim at minimising the damage or the extension of the damaged zone inorder to enhance the seal’s effectiveness. In order to prevent potentially damageable effects from therockbolts on the argillite’s integrity, the use of rockbolts will be avoided and replaced by a groundsupport using steelsets and 30 cm thick shotcrete. The drift shape can be made to resemble a circularform by locally reducing the usable diameter (5.2 metres).Figure 7.4.4Possible drift section in a seal zone121 This arrangement also facilitates the turning of more bulky vehicles (B and CU package transfer vehicles).DOSSIER 2005 ARGILE -ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL DISPOSAL SYSTEM302/495