Investigation of swelling behaviors of GMZ bentonite pellet mixtures

Bentonite pellet mixtures have been recognized as an effective backfilling material for the sealing of boreholes and tunnels during the construction of engineering barrier system in deep geological disposal of high-level radioactive waste. Once installed in the repository, the complicated hydro-mechanical coupling conditions may affect the swelling properties of pellet mixtures. In this study, a series of swelling pressure tests and swelling deformation tests were conducted on GMZ bentonite pellet mixtures. Results showed a good linear relationship between final swelling pressure and void ratio in swelling pressure test. Similar phenomenon was also observed between the upper loading and void ratio in swelling deformation test. Furthermore, suction effects on swelling pressure and swelling strain of bentonite pellet mixture indicated that, at high suction stage (> 4.2 MPa), the swelling of specimens was mainly controlled by the crystalline swelling and the exfoliation of clay particles. At lower suction stage (< 4.2 MPa), significant increases on swelling pressure and swelling strain were found, which might be related to osmotic swelling.