Bimodal pore size distribution of a high-plasticity compacted clay

The microstructure of compacted clay plays an important role in its hydraulic and mechanical behaviour. However, little experimental evidence is available for high-plasticity clay compacted on the wet side of the standard Proctor optimum water content. The results of an oedometric and microstructural investigation (mercury intrusion porosimetry) on reconstituted and compacted high-plasticity clay are presented. The microstructural results indicate that a bimodal pore size density function is not limited to clays compacted on the dry side of the standard Proctor optimum. The compacted clay prepared on the wet side can display a bimodal pore size distribution dependent on the level of compaction, current void ratio and degree of saturation. The bimodal distribution of the compacted clay can be lost by compression to high vertical stress accompanied by an increase in the degree of saturation. In this case the compression path ultimately approaches the normal compression line of the reconstituted saturated material. The results demonstrate that the observed behaviour of the compacted clay can be interpreted with reference to the reconstituted clay.