Abstract: The pile foundation of bridges and subgrades in high-speed railway engineering are frequently suffered from train-induced vibration. The train-induced vibration under a speed of 350 km/h reaches approximately 40 Hz, while a higher speed may do harm to the bearing capacity of the pile foundation. The soil-structure interface plays an important role in force and deformation transformation in pile-soil interaction, largely determining ultimate strength and long-term settlement. However, understanding of the behavior of soil-structure interfaces under high-frequency vibration is still very limited. Using a self-designed interface shear apparatus, which can achieve coupled vibration and high-frequency vibration, the critical state strength of the granular material-structure interface is investigated. The influences of vibration acceleration, frequency, normal stress, particle shape and surface roughness are studied. Test results show that vibrations lower the strength of interfaces. The shear strength under certain vibration conditions is even lower than half of that under static conditions. The weakening degree of interface strength under vibration increases with vibration acceleration and frequency, while decreases with normal stress. Based on Mohr-Coulomb strength theory, the strength criterion of the granular material-structure interface under vibration is built.

Key words: granular material-structure interface, high-frequency vibration, shear strength, vibro-induced weakening, coupled vibration and monotonic direct shear