Abstract: The importance of long-term stability of any structure makes the time effect of soil is one of the most concerned problems in geotechnical engineering. In this study, the creep tests on the equivalent sand particles of three-dimensional (3D) printed rods under lateral confined condition are conducted. In the tests, the internal particle motion characteristics of dense sand during creep and its relationship with macroscale creep deformation are explored from the perspective of single particle motion and contact motion between particles based on the close-range photogrammetry and particle image velocimetry (PIV) technology. The test results show that the 3D printed rod can reflect the macroscale deformation characteristics of dense sand during creep well. Under the lateral confinement, the creep deformation increases with the increase in time and decreases with the increase in creep stress, and the creep rate decreases and tend to be stable at the initial and secondary creep stages. This can be explained by that at the initial stage of creep, the particles move downward and rotate greatly which makes the pores between particles obviously reduced, and the creep deformation is mainly induced by the compression of pores between particles; then, the pores between particles do not decrease obviously and tend to be stable, the particles move in irregular directions, which indicates that the creep deformation is mainly controlled by local particle position adjustment and rearrangement. This also reveals that the macroscale creep deformation is closely related to the microscale translational change of particles. The contact motion between particles increases obviously with increasing time. During creep, contact rolling and contact sliding occur simultaneously, and gradually concentrate on some contacts that are easy to move. There is a good linear relationship between the average contact sliding distance and rolling distance of the strong moving contacts, i.e. with the increase of time, the average contact sliding distance is gradually greater than the average contact rolling distance, indicating that the sliding produces volume contraction and controls the macroscale creep deformation.

Key words: dense sand, creep, particle motion, translation, rotation