(1. Key Laboratory of Geotechnical and Underground Engineering of Ministry of Education，Tongji University，Shanghai 200092，China；2. School of Geosciences and Info-Physics，Central South University，Changsha，Hunan 410083，China)
Abstract：Bentonite pellets have been recognized as a new form of buffer/backfilling material in the construction of a multi-barrier system for high-level waste(HLW) disposal，which is primarily due to their cost-effectiveness in production，easy transportation and convenient installation. In this study，a series of suction-controlled hydration/unhydration tests and microscopic tests were performed on GMZ bentonite pellets using the vapor equilibrium technique. The objective was to investigate the water retention property，volume-change behavior，and micro-structural evolution of the pellets. The results demonstrated that the wetting/drying water retention curves of single bentonite pellet exhibited a hydraulic hysteresis at high-suction stage，but this phenomenon was less pronounced at low-suction stages. Bentonite pellets underwent a expansion with the absorption of water and a shrinkage with the loss of water during a wetting/drying cycle. This process led to the generation of plastic deformation at the high-suction stage. As inter-aggregate pores increased during the wetting process，the pore size distribution curve of bentonite pellets gradually transitioned from a unimodal porosity to a bimodal one. Even during the subsequent drying process，the curve continued to exhibit a bimodal porosity because the inter-aggregate pores were unable to fully recover. The BExM model effectively reproduced the swelling or shrinking behaviors of bentonite pellets during wetting and drying processes. Additionally，it was also used to analyze the changes of multi-scale pores within the bentonite pellet mixture，including the examination of intra-aggregate pores，inter-aggregate pores，and inter-pellet pores.
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2024, Vol. 43 
