Dual Porosity and Secondary Consolidation

In this paper, the results of a series of experiments using one-dimensional oedometer testing, mercury intrusion porosimetry (MIP), and scanning electron microscopy are reported on kaolinite samples with known and controlled fabric associations to reexamine the dualporosity hypothesis for the underlying mechanisms of secondary consolidation. The oedometer testing results indicate that the pH 7.8 sample (face-to-face aggregated structure) has the smallest values of compression index, Cc, and secondary compression index, C (alpha). The pH 4 sample (flocculated but dispersed structure) has the largest values, while the pH 7.8 with salt sample (flocculated and aggregated structure) has medium values. The C(alpha)/Cc ratios for these three samples are similar regardless of the structure and consolidation pressure. The MIP results on pore-size evolution in the pH 7.8 with salt sample show that both primary and secondary consolidation processes preferentially occur in the larger and weaker interaggregated pores instead of in the smaller and stronger intraaggregate pores. These oedometer testing and MIP results do not support the dual-porosity hypothesis, whereas they suggest that the primary and secondary consolidation processes involve the same physical factors.