Abstract: Based on the digital image correlation (DIC) technology， the mechanical properties on the interface between garvelly sand and concrete pipe were studied systematically under a constant normal stress condition by using a self-developed visual direct shear container. The experimental results showed that the initial shear modulus of the interface between gravelly sand and concrete pipe increases with the increase of normal stress. When D_r=0.8， the friction coefficient of the interface increases about 17.5% compared with that when D_r=0.4， and when the relative density increases by 0.2， the friction angle increases by 2° on average. The softening degree of the shear stress vs. shear displacement curve of the interface is gradually reduced with the increase of normal stress， and the hardening degree is gradually obvious. In addition， the shear displacement of the soil increases with the increase of the distance away from the interface. The shear deformation mainly occurs in the shear zone， and the thickness of shear band is 3D₅₀.

Key words: gravelly sand, direct shear test, interface properties, shear band, digital image correlation measurement