Permeability variation of bentonite-sand mixture due to shear strain

The objective of this study is to investigate the permeability variation of the compacted bentonite-sand mixture, a candidate material to be used in low level radioactive nuclear waste geotechnical disposal facility, due to shear deformation which might occur in the mixture caused by the earthquake and/or the nonuniform deformation in its long term performance. To execute the study systematically, a coupled shear and permeability testing apparatus was firstly developed in which a hollow cylindric specimen and the constant flow pump was adopted. It enabled us to measure the permeability along the shear plane in the specimen successfully and rapidly. The result of this study revealed that the permeability of the compacted bentonite-sand mixture with 15% of bentonite was not significantly influenced by the shear deformation. This has tentatively shown the effectiveness of both the new coupled shear and permeability testing apparatus and the bentonite-sand mixture to be used for retarding the radionuclide migration around the radioactive waste repository accompanying water movement.