Influence of strain-rate on hydromechanical behavior of highly compacted GMZ01 bentonite

• Step-wise constant strain rate compression tests were conducted.
• Parameters κ and λ of compacted GMZ bentonite decrease as suction increases.
• The yield stress p0 increases as suction and the strain rate applied increase.

During the long-term operation of a deep geological repository in crystalline rock, saturation of buffer/backfill materials will last for a long period of time. Investigation on time-dependent property of buffer/backfill materials is of great importance for long-term safety assessment of the repository. In this work, GMZ01 bentonite powder was statically compacted to specimens with a dry density of 1.70 g/cm3 and suction-equilibrated to their target values. Then, a series of suction-controlled constant rate of strain (CRS) tests (including single-stage and step-wise CRS tests) were conducted for the investigation of the strain rate-dependent compression behavior of highly compacted GMZ01 bentonite. Comparisons were made between the results of the single-stage and step-wise CRS tests under given suctions for the verification of the applicability of the isotache concept on the compacted GMZ01 bentonite. Based on that, the step-wise CRS compression tests were performed and results were presented in terms of vertical stress–vertical strain curves. Based on the test results, the virgin compression index λ and the yield stress p0 were determined. Analysis indicates that λ decreases, while p0 increases with increasing suction. Furthermore, p0 increases with increasing CRS, which is consistent with previous researches on saturated soils. Finally, a logarithm function proposed between α(s) and suction s is verified and several relevant parameters are fitted, which represents the coupling of suction, time and stress of GMZ01 bentonite.