Permeability Variation of Bentonite-Sand Mixture Due to Shear Strain
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PERMEABILITY VARIATION OF BENTONITE-SAND MIXTURE DUE TO SHEAR STRAIN MING ZHANG*, T. ESAKI* AND Y. MITANI** * Kyushu University, Faculty of Eng., Hakozaki 6-10-1, Higashi-ku, Fukuoka 812, JAPAN **SHIMIZU Corporation, Shibaura 1-2-3, Minato-ku, Tokyo 105-07, JAPAN
ABSTRACT 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.
INTRODUCTION In the process of low level radioactive waste disposal, bentonite-sand mixture with an exthe repositories to retard the seepage or migration of radionuclides[1,2]. However, in its long term performance, there is a potentiality that the permeability of the mixture would increase due to shear deformation caused by earthquake and/or nonuniform deformation, i.e., the expected effect of the mixture for retarding the water movement would be decreased. In regard to this kind of problem, it is necessary to understand the effect of shear deformation on the permeability variation of the mixture, or the allowable shear strain that will not sharply increase the permeability of the mixture. To execute the laboratory study on the above problem, a coupled shear and permeability testing apparatus was developed based on the discussion of the existing methods of both shear test and permeability test. The adopted shear method was an approach for testing a hollow cylindrical specimen in plane strain state under different internal and external pressures. Coupled with the constant flow method, it enabled us to measure the permeability along the shear plane in the specimen successfully and rapidly. This paper presents the design of the newly developed testing apparatus and some findings obtained from the coupled shear and permeability test on the compacted bentonite-sand mixture. tremely low permeability has been proposed as a candidate material for filling the zones around
COUPLED SHEAR AND PERMEABILITY TESTING METHOD To simultaneously conduct the shear and permeability test is very difficult. It has not yet been developed to technical maturity. So far, only a few tests have bee
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