Temperature Effect on the Deformation Behaviour of Compacted Bentonite Under Free Swelling/Shrinkage Conditions

Compacted bentonite is considered as the most suitable buffer/backfill material in deep geological disposal of high-level radioactive waste. During the operation of deep geological repository, the ambient temperature of bentonite is constantly changing under the coupled effect of radioactive wastes decay and groundwater immigration. This induces the volume changes, and thus affects the engineering properties of buffer materials. In this paper, a series of swell/shrinkage tests upon suction decrease/increase were conducted on cubic bentonite samples at different temperatures of 20, 40 and 60 degrees C. The suction decrease or increase was realized by using vapor equilibrium method, while, the temperature was controlled by using numerical oven with thermostats. During the test, the sample dimension in both vertical and horizontal direction was regularly measured with a high accuracy laser displacement sensor. Variations of sample dimension over time at different temperature were obtained, base on which, the strain-suction relationship as well as the anisotropy of sample deformation were analyzed at different temperatures. It can be found that the deformation amount and suction equilibrium time of the sample at the same temperature are affected by the gap between initial suction and target suction. And the rise in temperature significantly weakens the sample deformation caused by suction change. The linear strain perpendicular to the compaction face of sample was larger than that parallel to the compaction face. And this anisotropy behavior was amplified by increasing temperature but independent with suction.