Particle size evolution of granular bentonite upon wetting and loading

Abstract

Granular bentonite (GB) presents a broad particle size distribution with granules reaching several millimetres. This distribution renders its compaction behaviour, governing the subsequent hydro-mechanical (HM) response, highly sensitive to variations in particle size. In case of fine-grain segregation, the breakage of coarse granules during compaction reduced the stress required for as-poured GB to attain the target dry density. Upon wetting under unstressed conditions, the as-poured dry density of GB decreased, while granule disaggregation occurred concurrently with the formation of low-density aggregates resulting from fine-grain aggregation. These aggregates protected adjacent granules from disaggregation and breakage during further wetting and loading. Consequently, wetter as-poured GB required higher compaction stresses to achieve the target dry density and exhibited reduced compressibility. These findings contribute to improving the design of GB-engineered barriers and advance insight into their long-term HM behaviour assessment.

This project has received funding from the European Union’s Horizon 2020 research and innovation programme ‘European Joint Programme on Radioactive Waste Management’ EURAD (2019-2024) WP GAS ‘Mechanistic understanding of gas transport in clay materials’ under grant agreement No. 847593. The authors acknowledge the support of NAGRA through the project ‘Scientific work related to barrier integrity’ Ref 18722 (2019-2024) and thank project PID2022-141429OB-I00, funded by the Spanish Ministry of Science/Research Agency MCIN/AEI/10.13039/501100011033/FEDER EU (2023-2027).

Postprint (published version)