Abstract: The evolution of particle structure influences the physical and mechanical properties of Nanjing silty fine sand. In this
study, consolidation undrained shear tests were conducted on Nanjing silty fine sand specimens using a self-developed miniature triaxial apparatus, with simultaneous synchrotron micro-CT scanning. Methods such as characteristic ellipsoid fitting, ball-stick model, and characteristic particle extraction were employed to quantitatively characterize and analyze the evolution of particle shape, contact relationships, and movement characteristics. The correlation between particle structure and pore structure evolution was also discussed. The results revealed that the specimens initially softened and then hardened during the test, exhibiting barrelshaped localized failure with bulging in the middle; the consolidation undrained shear process had a certain rounding effect on Nanjing silty fine sand; the contact area between particles and the pore coordination number were found to be more sensitive to failure occurrence than the particle coordination number, which was generally lower than the pore coordination number throughout the process; the rotation of particles affects the development of the pore network in the specimen; horizontally, there was a central position in the specimen where the horizontal displacement of particles was minimal, and vertically, a conical interface existed in the failure zone, with significant differences in vertical displacement of particles on either side, which serves as the internal cause of the localized failure. The research findings contribute to a deeper understanding of the micro-mechanisms underlying the evolution of the macroscopic engineering properties of saturated Nanjing silty sand and can provide support for the study of the resilience of river floodplain geological environments and urban safety.

Key words: Nanjing silty fine sand, triaxial compression, synchrotron radiation micro-CT, 3D reconstruction, particle structure
evolution