Anisotropic characteristics of swelling pressure for compacted GMZ pie-shaped bentonite block

In China, Gaomiaozi (GMZ) bentonite has been selected as the first choice of buffer/backfill materials for high-level radioactive waste repository. In order to investigate the anisotropic characteristics of swelling pressure for compacted GMZ bentonite, a series of swelling pressure tests were conducted by a self-developed apparatus on the pie-shaped block specimens to measure the axial and radial swelling pressure, and then the effects of initial dry density, initial suction and dimension on the anisotropy were analyzed. The results show that with the increase of the initial dry density, the axial swelling pressure and radial swelling pressure exponentially increase, and the anisotropy of swelling pressure tends to be more obvious. Both the axial and radial swelling pressures decrease with the increase of the initial suction of the specimen; for the same initial suction, the radial swelling pressure is greater than the axial swelling pressure; moreover, the anisotropy coefficient decreases as the initial suction increases. Meanwhile, swelling pressure is remarkably affected by specimen dimension, because with the increase of specimen height, the axial swelling pressure increases gradually, while the radial swelling pressure increases and remains constant until a certain value is reached; therefore, the anisotropy coefficient gradually reduces as the height increases. Furthermore, the anisotropy mechanism of the swelling pressure was analyzed based on the swelling process, compaction effect and size effect. © 2019, Editorial Office of China Civil Engineering Journal. All right reserved.