Performance evaluation of compacted bentonite buffer material at shear failure

Compacted bentonite is planned for use as a buffer material in the geological disposal of the high-level radioactive waste. In this paper, in order to study the failure behavior of the compacted bentonite, a series of constant volume direct shear tests were performed. Developed shear bands were observed during the direct shearing using the PIV image analysis. Also, inside of the specimens were observed by using µ -focus X-ray CT scanner. Even though the process of shear bands formation in the unsaturated over-consolidated specimen was different from the process in unsaturated normally consolidated specimen, the low density region due to the shear failure was hardly observed in the center of both specimens under the relative high vertical stress condition. In the case of saturated specimens, there was no change of density at the shear band, and also, it has been confirmed that sealing performance does not change after development of shear bands.