Tome Architecture and management of a geological repository - Andra

4 - General architecture of the repository in a granite mediumFigure 4.2.8Basic diagram of a drift sealA swelling clay coreThe confinement of the clay core by the concrete abutments keeps the swelling pressure of the clayover 1 MPa. The hydraulic conductivity target for the clay is about 10 -11 m/s. This may be achieved byadopting dry density of about 1.5 for the swelling clay if the clay is pure, and 1.75 in the case of a clay(70%) and sand (30%) mix.The choice between pure clay of the MX80 type, Kunigel V1, used for the TSX experiment or DeponitCA-N examined by SKB or a blend of that sort of clay with sand, does not appear to be a decisivefactor at this time [16] [17].At this stage, it is considered that a core length of 10-15 m should enable sufficient non-transmissivecontact to develop between the swelling clay and the undamaged (sound) granite.A concrete abutmentAn un-reinforced concrete abutment is constructed at each end of the core. The two abutments aredimensioned to withstand the swelling clay pressure by taking support on the over-excavationshoulders. Transferring the abutment pressure to the compacted backfill emplaced in the driftsupstream and downstream of each seal ensures redundancy in the core’s mechanical confinementmechanism.Each of these two abutments is equivalent in length to the width of the drift in which it is constructed,and a shoulder that incorporates a support surface some fifty centimetres wide on undamaged graniteis planned.High performance low pH concrete whose formulation enables thermal shrinkage to be minimised atthe interface between the abutments and the surrounding granite, may be used.Dossier 2005 Granite - ARCHITECTURE AND MANAGEMENT OF A GEOLOGICAL REPOSITORY72/228