Study on microstructural evolution of soft clay under one-dimensional consolidation

Undisturbed marine soft clay from Daya Bay in Shenzhen poses severe geotechnical challenges owing to its high sensitivity and low shear strength. In this study, the microstructural evolution and underlying mechanical mechanisms of this soft clay under one-dimensional consolidation were systematically investigated. A multi-scale analytical approach was adopted, integrating Mercury Intrusion Porosimetry (MIP), dual-energy synchrotron X-ray Micro-Computed Tomography (Micro-CT) with phase recovery technology, and Discrete Element Method (DEM) simulations implemented in PFC3D 6.0. The results show that one-dimensional consolidation induces a distinct structural transition of the clay's pore size distribution from bimodal to unimodal, with the connectivity of macropores being completely destroyed under high consolidation pressure. Two structural yield stresses were identified at 62 kPa and 676 kPa, corresponding to the structural failure of inter-cluster aggregates and intra-cluster particles, respectively, which characterizes the mechanical transformation of the clay from aggregate rearrangement to intra-aggregate compression. Numerical simulation results further demonstrate that the increase in consolidation pressure leads to a gradual rise in the particle coordination number and a significant decrease in the contact-sliding ratio, thereby enhancing the structural stability of the clay skeleton. These findings establish a quantitative correlation between the microscopic pore structure reorganization and macroscopic mechanical response of soft clay, and provide a robust mechanistic basis for accurate settlement prediction and ground improvement design in coastal geotechnical engineering.