Macro and mesoscopic shear behavior of interface between sand and concrete with different JRC under cyclic load

To investigate the interaction mechanism between the sand–structure interface under cyclic loading, a series of cyclic direct shear tests were conducted. These tests were designed with various surface roughness values represented by the joint roughness coefficient ( JRC ) of 0.4, 5.8, 9.5, 12.8, and 16.7, and normal stresses of 50, 100, 150, and 200 kPa. A 3D printer was employed to accurately control the surface roughness and obtain concrete samples with varying JRC values. The test results were used to establish discrete element method models, which facilitated the analysis of the mesoscopic shear behavior at the sand–structure interface during the cyclic direct shear process. The results revealed that the sand–concrete interface demonstrated softening behavior. There is a critical value for the surface roughness corresponding to the maximum interface shear strength. The thickness of shear band, where the changes in porosity were concentrated within, increases with higher surface roughness and cycle number. The coordination number stabilizes after 80 cycles. The distributions of the contact normal direction and tangential contact force exhibited nearly isotropic characteristics after cyclic loading. It was observed that surface roughness amplifies the deflection angle of the main axis in the normal contact force distribution, while reducing that in the shear contact force distribution.