A compacted mixture of Kunigeru VI bentonite and D-sand is being consideredfor use as an engineered barrier in low-level radioactive waste disposalfacilities in Japan. An important issue is the maintenance of theretardation property of the mixture during shear that might be induced insuch barriers by earthquakes and/or gradual tectonic deformations occurringover the design life of the facility. To investigate this issue, comparativetests on a bentonite-sand mixture and kaolin-sand mixture were conducted bymeans of a recently-developed coupled shear and permeability testingapparatus under temperature controlled condition. In addition topermeability, the specific storage of bentonite-sand specimen during shearis also systematically evaluated with the new analytical theory for theconstant flow permeability test. The present study reveals that 1)temperature control is preferred for measuring the permeability ofextremely-low permeability materials with the constant-flow pump method; 2)both the permeability and specific storage of the mixture of Kunigeru VIbentonite and D-sand (bentonite to sand weight ratio = 15: 85) were notsignificantly influenced by shear strains up to 3% whereas the permeabilityof the kaolin-sand mixture increased almost linearly with the increment ofshear strain; 3) the swelling of bentonite in the mixture under lowconfining stress decreases both the permeability and specific storage ofbentonite-sand mixture. This feature of bentonite helps maintain thelong-term retardation property of the mixture; and 4) the constant flowpermeability test method, with the newly derived theoretical analysis,promises to become a very effective means of investigating, rapidly andsystematically, the permeability and specific storage of extremely-lowpermeability materials with relatively-low (i.e. close to in situ) hydraulicgradients. This is necessary for the design and long-term performanceassessment of engineered barriers.