<p>The bearing capacity of pile foundations critically depends on the shear behavior at the pile-soil interface. However, current research primarily addresses static loading, with limited studies on quasi-static cyclic shear under realistic boundary conditions. A large-scale structural-soil interface cyclic shear apparatus was utilized to conduct cyclic shear tests on the Yellow River silty soil-pile interface under constant stiffness conditions. The variation laws of interface shear stress, normal stress, shear stress ratio, and interface shear stiffness were investigated under different shear displacement amplitudes, roughness, and initial stress levels. The results indicate that the area under the shear stress hysteresis curve of the Yellow River silty soil-pile interface increases with increasing shear displacement amplitude, and the peak shear stress correspondingly increases as well. The larger the interface roughness, the greater the peak shear stress observed. The normal stress initially decreases and then stabilizes with the increase in the number of cycles, particularly under conditions of large shear displacement amplitude and roughness, where the decrease in normal stress is more pronounced. The relationship curve between shear stress and normal stress exhibits a butterfly-shaped variation characteristic. The shear stress ratio decays exponentially with the increase in the number of cycles, with a small attenuation amplitude at an initial stress level of 200&#xa0;kPa, but the highest degree of attenuation at a shear displacement amplitude of 5&#xa0;mm. The interface shear stiffness gradually decreases with the increase in the number of cycles and is significantly affected by the amplitude of shear displacement and initial stress level, while being relatively less influenced by roughness.</p>