Abstract: To investigate the long-term mechanical properties of the interface between calcareous sand and structure, a strain-controlled direct shear apparatus and a triple rheological direct shear test system were employed. Shear and shear creep tests were conducted on both calcareous sand itself and its interfaces with surfaces of varying roughness levels. The effects of normal stress and interface roughness on the instantaneous and long-term shear strength of the interface were analyzed, and the results compared with those of pure calcareous sand. The results show that the displacement following interface shear creep is smaller than that of the calcareous sand alone. Increasing normal stress enhances both the long-term and instantaneous strength of the interface, but their ratio decreases, ranging from 66.2% to 76.2%. Compared to the calcareous sand, the interface exhibits lower instantaneous strength, long-term strength, and strength ratio. Increasing interface roughness leads to increases in long-term strength, instantaneous strength, cohesion, and internal friction angle; however, the rates of increase in strength and internal friction angle diminish as roughness inceases. Furthermore, the increase in long-term strength is less pronounced than that in instantaneous strength.