<p>The soil-structure interface typically represents the weakest point in a structure. Elucidating the shear mechanism at this interface is crucial for resolving issues such as bearing capacity deficiencies and shear strength limitations in precast structures. To investigate the effects of interface roughness and structural inclination angle on interface shear strength, this study implemented Triaxial Contact Surface Shear Tests to characterize interfacial shear behavior of saturated soft clay-structure contact interfaces. Distinct interface roughness levels and structural inclination angles were configured to systematically analyze the mechanical properties of the soft clay-structure contact interface. The results show that the interfacial shear strength demonstrates a positive correlation with interface roughness. In addition, the structural inclination angle significantly modulates the shear strength response, with interfacial shear stress progressively increasing as the inclination angle increases. Under both parametric conditions, the stress–strain curves exhibit strain-hardening behavior. Moreover, increased interface roughness induces pronounced variations in the internal friction angle, demonstrating linear relationship with shear stress. In contrast, the structural inclination angle follows an exponential relationship with the internal friction angle and shear stress. Subsequently, predictive formulations for the internal friction angle and interfacial shear stress of saturated soft clay-structure interfaces across different inclination angles are proposed, while accounting for the influence of roughness. These findings provide a reference for selecting interface parameters in soft clay-structure systems, and the proposed predictive equations offer guidance for designing and constructing precast structures at varying inclination angles.</p>