Microstructure evolution of saturated clay under cyclic shearing

Changes in soil microstructure are important for understanding the macro-behavior of soil. Studies in the past have mainly focused on analysing variations under isotropic and one-dimensional consolidation. The present study aims to investigate the microstructure evolution of saturated clay under cyclic shearing. Cyclic triaxial tests are carried out under different magnitudes of effective confining pressure, cyclic deviator stress, and overconsolidation ratio (OCR). The soil microstructure is determined through the scanning electron microscope and mercury intrusion porosimetry tests. It is observed that there is a threshold cyclic deviator stress, above which the soil specimens show significant plastic strain and eventually fail. The threshold value is found to increase almost linearly with the increase of effective confining pressure and OCR. On the other hand, when the cyclic deviator stress is higher than the threshold value, some large pores appear even though the total pore volume is kept constant (undrained condition under cyclic loads). With the appearance of some larger pores, the soil skeleton becomes weaker and eventually fails.