The points of attention for evaluating swelling pressure and hydraulic conductivity of compacted bentonite by laboratory tests

Compacted bentonite and bentonite-based materials with low hydraulic conductivity will be used as engineered barriers to inhibit the migration of radioactive nuclides. In this paper, the points of attention for conducting swelling pressure tests and hydraulic conductivity tests of compacted bentonite in the laboratory and for modelling the test results are described. It was found that the swelling pressure test results of compacted bentonite, which are affected by several factors, such as the stiffness of the test cell, the height of the specimen, and the initial degree of saturation, can be numerically simulated using the numerical model proposed previously. It was also found that evaluating the equilibrium swelling pressure by the diffusion double layer theory, it is necessary to pay attention to the setting of the interlamellar distance. As for the hydraulic conductivity test, measurement method of B-value in the rigid wall permeability testing apparatus was proposed because it is difficult to calculate saturation of samples with large fluctuations in soil particle density. Furthermore, in the case of using a flexible wall permeability test apparatus for undisturbed samples, an example of a new contrivance for preventing the specimen density and the cell pressure from becoming excessively large was shown. (author)