Volume 48 (2008) Issue 3 Pages 363-374
For the purpose of establishing the method for estimating in-situ mechanical behavior of artificial buffer materials, stress-deformation behavior of bentonite-sand mixtures were investigated through oedometer test, consolidated undrained triaxial compression test and expansive stress-strain measuring test by changing the clay content as 30, 50, 70 and 100%, and by changing the range of initial dry density of mixture from 1.4 to 1.8 g/cm3. Oedometer test results suggest that the magnitude of consolidation yield stress almost coincides with the maximum expansive stress (p′s)max irrespective of bentonite-sand mix proportion, initial density of mixture and the magnitude of molding stress at the specimen making. Strong correlation between consolidation stress and initial tangent modulus during undrained triaxial compression test is observed, and it is found that the reduction rate of rigidity is hardly dependent on the specimen making method, molding stress and the consolidation stress. From the two series of expansive stress-strain measuring tests, it is recommended to perform the measurement of expansive stress by feed back system with the load cell installed at the base of the specimen. A unique relationship is found between the maximum expansive stress (p′s)max versus bentonite specific volume vb, which is defined as the specific volume calculated by excluding the volume of sand particles. The line showing the unique log vb versus log (p′s)max relationship can be recognized as the state boundary line prescribing one-dimensional expansive stress-strain behavior of the bentonite-sand mixtures.