Abstract: The movement behavior of soil particles near pile foundation is closely related to the macroscopic mechanical performance, which is of great significance to reveal the interface shear mechanism. By using the self-developed large-scale direct shear instrument and the 3D-DIC full field displacement measurement system, cyclic shear tests of interface between steel plate and calcareous were carried out to examine the motion behavior of sand particles near the interface. The results show that the peak interface shear stress and the developed friction angle of interface increase with the number of cycles, and shear shrinkage is the main characteristic of volumetric deformation. The range of left-right movement of calcareous sand particles is inversely proportional to their vertical distance from the interface. The position of calcareous sand particles gradually moves to the positive shear direction with the number of cycles. At the end of the test, the calcareous sand particles in the left area of the upper shear box move a large distance towards the positive shear direction. Calcareous sand particles move up and down regularly in a single cycle, which is mainly characterized by downward movement. The downward movement displacement of calcareous sand particles far from the interface is greater than that closer to the interface. The movement speed of calcareous sand particles shows a slow-fast-slow change law when shearing along the single direction. The volume deformation characteristics of calcareous sand on the right region of the upper shear box are more obvious than those on the left region. The displacement value of the grid and the number of missing grids increase with the number of cycles, and tend to be stable in the later stage of the test. At the end of the test, the thickness of the breakage zone is 6.21 mm.

Key words: calcareous sand, interface shear, particle motion, coordinate, displacement nephogram, breakage zone