Dynamic response of bridge pile foundation near fault under strong earthquake

In order to find out the difference in the dynamic responses of bridge piles on the hanging wall and footwall of the fault under a strong earthquake, relying on the Haiwen Bridge project in Hainan Province, the shaking table model test was carried out to study the response differences of pile acceleration, pile top relative displacement and pile bending moment response laws, and the piles damage characteristics on the hanging wall and footwall of the fault under the action of 0.15g-0.60g ground motion intensity. Research result shows that the difference between pile top peak accelerations on the hanging wall and footwall of the fault is 0.291-0.488 m·s^-2, and the difference in the amplification factor of pile top acceleration is 0.067-0.195 under the different ground motion intensities. The reason is the difference in the influence range of the fault on the rock and soil mass on both sides and the "non-linear" difference of the rock and soil mass around the pile. With the increase of earthquake intensity, the difference between the pile top relative displacements on the hanging wall and footwall of the fault increases gradually, and the maximum difference is 0.77 mm. The difference between the maximum bending moments of the pile foundations on the hanging wall and footwall of the fault is 5.294-82.932 kN·m, and the maximum bending moment occurs at the interface of soft and hard soil and near the bedrock surface. The reason is that the footwall, as a stable plate, is squeezed by the soil mass of the hanging wall, which has a certain inhibitory effect on the vibration and shear of the rock and soil mass of the footwall. When the ground motion strength is 0.35g, the maximum bending moment of the pile on the hanging wall and footwall of the fault does not exceed the bending bearing capacity, which meets the requirement of seismic fortification intensity Ⅷ of Haiwen Bridge(0.35g). When the ground motion intensity is 0.35g-0.45g, the pile fundamental frequency on the hanging wall of the fault has a small variation range. When the ground motion intensity is 0.50g-0.60g, the pile foundation frequency on the hanging wall decreases significantly. The cracks appear at the connection between the pile top and cap, the interface between the soft and hard soil layer, and the bedrock surface, which shows that the piles have been damaged. In summary, the acceleration of pile, the relative displacement of pile top, and the bending moment of pile on the hanging wall are larger than those on the footwall. The dynamic response changes of the piles on the hanging wall and footwall of the fault are significantly different, which shows significant "the hanging wall effect of fault". Therefore, in the seismic design of bridge pile foundation near the fault under strong earthquake, the seismic capacity of hanging wall pile foundation should be considered.