Abstract: In high-level radioactive waste(HLW) repository, buffer backfilling material should be pre-compacted to a certain density. The compression properties of buffer backfilling material have an important influence on the safety design, construction and operation for geological HLW repository. At present, bentonite-sand mixtures are considered to be the ideal buffer backfilling material in the geological HLW repository in China. the compression properties of bentonite-sand mixtures with different dry densities and sand ratios, whose water content is constant, are performed by WG oedometer. It is found that the compression coefficient a1-2 decreases quadratically with the increase of dry density, but it increases nonlinearly with the increase of sand ratio. Based on the concepts of effective clay density and effective water content, we try to explain the changes of the compression coefficient a1-2 with dry density and sand ratio. The regression analysis model of bentonite-sand mixtures with various dry densities and sand ratios are fitted based on the experimental data, and it hopes that this result can be used to provide a related basis of the optimization of buffer backfilling material.

Key words: bentonite-sand mixtures, compression properties, high-level radioactive waste(HLW), buffer backfilling material