The study of pile-soil interface under cyclic loading is an important research direction of pile-soil interaction. The degenerate effects of pile-soil interface under cyclic loading consist of degenerate shear stress

degenerate normal stress

and the breakage mechanism of sand particles

which interact with each other and control the bearing capacity of pile-soil interface. Interfacial roughness has important influence on pile-soil mechanical mechanism. Macroscopic and microscopic mechanism of cyclic degradation behavior on pile-sand interface under different interface roughness was researched by utilizing self-developed visual constant normal stiffness (CNS) interface shear apparatus combined with digital image correlation (DIC) measurement technology. The experimental results showed that the relation curves of shear stress and normal stress developed as “hysteretic loop” and “disk” shapes

respectively. Under the same roughness

the interfacial shear stress and the normal stress both degraded logarithmically with the increase of the numbers of the cycles

while this degradation rate increased with the increase of interfacial roughness. The stress path curve developed as a “butterfly ring” shape

and the friction angle increased with the increase of interfacial relative roughness. The interfacial shear band was gradually thickened with the increase of shear cycles and interface roughness

and this thickness reached about (4-5) D50 after 30 cycles. In addition

the particles in the shear band were significantly broken and the relative crushing rate was 1.86%-10.25%

which increased with the increase of interfacial roughness.