Microstructure study of natural marine clay in loading and unloading processes

Abstract

The microstructure evolutions of natural marine clay during loading and unloading processes were investigated using undrained triaxial tests. The pore distribution and arrangement of soil particles and aggregates were measured by mercury intrusion porosimetry (MIP) and field emission scanning electron microscope (FESEM) tests, respectively. The results show that pores do not always collapse into smaller ones with stress levels increasing; the destruction of cemented soil structure will lead to the connection of small pores into large pores. In the consolidation process, as the consolidation pressure increased from 0 to 100 kPa, the total specific surface decreased from 20.01 mm2/g to 17.42 mm2/g. Conversely, the total specific surface increased from 17.42 mm2/g to 19.25 mm2/g as the confining pressure surpassed the preconsolidation pressure, indicating the formation of new surfaces. The rebound effect during the unloading process is another factor causing the increase in pore volume, but the destruction of the soil structure can significantly reduce this effect. The microscopic morphology at the point of soil failure under high stress levels in both loading and unloading processes tended to be similar, as the soil structure was completely destroyed.