Mechanism of Microstructural Variation Under Cyclic Shearing of Shantou Marine Clay: Experimental Investigation and Model Development

Abstract

Soil microstructure has been extensively studied in recent years, because it can provide insights into macro behaviour. Previous studies in this area mainly focus on the change in soil microstructure during isotropic and one-dimensional consolidation. The principal objective of this study is to investigate the mechanism of microstructure evolution of soft marine clay under cyclic shearing. Cyclic triaxial tests were carried out at various confining pressures, cyclic deviatoric stresses and over-consolidation ratios (OCR). Soil microstructure was determined using the scanning electron microscope (SEM). Artificial neural networks (ANN) were used to develop a model for understanding the interaction effects of different parameters (number of cycles, cyclic deviatoric stress) on axial strain at different confining pressures (60, 80, 100 and 150 kPa). It was found that there is a threshold cyclic deviatoric stress, above which soil specimen shows significant strain and eventually fails. The threshold value is found to increase almost linearly with an increase in confining pressure and also, increases with increasing OCR. On the other hand, the change of soil microstructure during the subsequent cyclic shearing depends on the magnitude of cyclic deviatoric stress. When the cyclic deviatoric stress is below a threshold value, the soil microstructure maintains almost unchanged. When the cyclic deviatoric stress exceeds the threshold value, some large pores appear even though the total pore volume is kept constant (undrained condition under cyclic loads). With an increase in pore non-uniformity, soil skeleton becomes weaker and eventually collapses.