Prediction of Swelling Pressure for Compacted Bentonite

Abstract:

Compacted bentonite has been selected as the potential buffer/backfill materials for the deep geological repository of highlevel radioactive nuclear waste; consequently the swelling pressure of compacted bentonite is the key index of its buffering performance. Based on the swelling process of compacted bentonite, the swelling mechanism, prediction models, and experimental verification of swelling pressure were systematically summarized. The existing predication models of bentonite swelling pressure are mainly based on the diffused doublelayer (DDL) theory. The laboratory tests demonstrate the influences of dry density, initial water content, sand content, and other factors on the final swelling pressure of compacted bentonite. The comparison between the model predication and the experimental results shows that the existing models have less fitting to the compacted bentonite with higher montmorillonite content and higher initial dry density. In fact, the swelling process of compacted bentonite includes crystalline swelling and DDL swelling, but the predication models are only used for estimating the DDL swelling, which cannot very well describe the crystalline swelling. The existing prediction models are only applicable to estimating the final swelling pressure of bentonite, but it is difficult to reflect the evolution process of swelling pressure caused by environmental changes during the longterm operation of repository.

Key words:nuclear waste repository; compacted bentonite; swelling pressure; crystalline swelling; diffusion doublelayer (DDL) swelling