Influence of Fluid Pressures on Shear Strength of Unsaturated-Saturated Bentonite-Sand Mixture

Safety of great deep repository design has been considered for high level radioactive waste disposal system in several countries such as Belgium, Canada, China, France, Germany, Japan, Sweden, and Switzerland etc. The repository of the disposal is in most cases based on the aspect of multi-barrier system used the natural barrier formation (i.e., host rock) and engineered barrier formation consisting of compacted bentonite. This study focused on direct shear strength for compacted bentonite related to some factors induced by uncertainty problems. A modified direct shear apparatus was used for investigation of efforts above mentioned factors on shear strength. The constant net normal stress (i.e., vertical stress) direct shear test was conducted out with various shear speeds. Also, it was possible to predict that the excess fluid pressures (i.e., gas pressure and pore-water pressure) were accumulated or were maintained in bentonite samples.