Compaction properties of granular bentonites

摘要

Bentonites have been examined recently in some countries as candidates for buffer materials for use in high-level nuclear waste repositories. Granular bentonites are anticipated as the raw materials for constructing bentonite-based buffer materials by in-situ compaction methods. For that reason, it is important to understand the influence of grain size distribution and physicochemical properties of bentonite ore on compaction properties of granular bentonites. This study performed the compaction tests of 21 kinds of granular bentonites. Compaction properties of granular bentonites depend not on the grain size distributions, but strongly on the kind of bentonite ore used as a raw material. The maximum dry density and optimum water content of granular bentonite are evaluated from the plastic limits of powdered bentonite ore. Granular bentonite with a lower plastic limit has higher maximum dry density and lower optimum water content. This fact implies that microscopic interaction between aggregate of montmorillonite in the bentonite and water supplied for adjusting the water content of sample plays an important role in the compaction process of granular bentonite. Therefore, compaction properties of granular bentonite, though classified gravel or sand from viewpoint of grain size distributions, should be treated similarly to those of clay materials. Calculations to establish evaluation methods for compaction properties of granular bentonites and observations of cross sections of dynamically compacted granular bentonites show that the compaction process of granular bentonite is controlled by the homogenization process of bentonite clay in the void space between load-bearing bentonites.