DEVELOPMENT OF SUCTION-CONTROLLED PERMRABILITY TEST FOR UNSATURATED BENTONITE-BASED BUFFER MATERIALS

Abstract

 Laboratory tests of the reliable relative water permeability of bentonite-based buffer materials are required for design and performance assessment of radioactive waste disposal facilities. A controlled-suction permeability test method under steady state is developed and a series of permeability tests for unsaturated sand/bentonite mixture are performed. Numerical simulations for the tests with coupled mechanical-two phase flow model are carried out to confirm applicability of the test to appropriately evaluating the relative permeability. In addition, the Gardner’s method as one of evaluation methods with unsteady permeability tests is discussed based on similar coupled numerical simulations. It is revealed that almost homogeneous water saturation corresponding to given suction and parallelly one-dimensional seepage flow are achieved in the test sample by the developed permeability test. It is found that the test can give reliable relative permeability with such achievement of steady state in the sample, while applicability of the Gardner’s method and attention/importance of setting suction increment according to material properties are suggested.