Influence of relative compaction and degree of saturation on the deformation characteristics of bentonite under freeze-thaw cycles

Abstract

Bentonite, consisting of clay minerals of the montmorillonite group, has been widely used as an adsorbent and backfill material in nuclear waste disposal and groundwater remediation. It is challenging to use bentonite as a filling material in cold regions since bentonite is highly sensitive to thermal environmental changes, during which its bulk volume and microstructure change significantly. In this study, a series of one-dimensional and three-dimensional freeze-thaw tests were carried out within a closed system to investigate the influencing factors of the deformation of bentonite under freeze-thaw cycles. Results show that the initial soil water content greatly impacts bentonite's deformation during freeze-thaw cycles. For an initial higher degree of saturation (S_r), the expansion caused by the formation of ice lenses has a greater impact than the shrinkage induced by dehydration, ice-cementation, and so on. Conversely, bentonite tends to shrink at a lower degree of saturation during freezing. And the critical degree of saturation that determines bentonite's behavior of frost heave or frost shrinkage seems to be roughly 0.8. As the number of freeze-thaw cycles rises, initially uncompacted bentonite clay becomes more compacted, and initially compacted bentonite clay remains unchanged.