强震作用下近断层桥梁桩基动力响应

为探明强震作用下断层上、下盘桥梁桩基动力响应差异，依托海南省海文大桥工程，通过振动台模型试验，研究了0.15g~0.60g地震动强度作用下断层上、下盘桩基的桩身加速度、桩顶相对位移、桩身弯矩响应规律差异与桩基损伤特征。研究结果表明：在不同地震动强度作用下，断层上、下盘桩基的桩顶加速度峰值相差0.291~0.488 m·s^-2，桩顶加速度放大系数相差0.067~0.195，原因为断层对两侧岩土体影响范围存在差异与桩周岩土体“非线性”差异；随着地震动强度的增大，断层上、下盘桩基的桩顶相对位移差值逐渐增大，最大差值为0.77 mm；断层上、下盘桩基的弯矩最大值相差5.294~82.932 kN·m，且弯矩最大值均出现在覆盖层软硬土交界面与基岩面附近，原因在于下盘作为稳定盘，受上盘土体挤压作用，对下盘岩土体的振动剪切有一定抑制作用；地震动强度为0.35g时，断层上、下盘桩的最大弯矩均未超过抗弯承载力，满足海文大桥抗震设防烈度Ⅷ度(0.35g)的要求；地震动强度为0.35g~0.45g时，断层上盘桩的基频变化幅度较小，地震动强度为0.50g~0.60g时，断层上盘桩的基频显著降低，在桩顶与承台连接处、软硬土层界面与基岩面附近出现裂缝，说明此时桩基已发生损伤。可见，断层上盘桩基的桩身加速度峰值、桩顶相对位移与桩身弯矩动力响应指标均大于下盘桩基，断层上、下盘桩基动力响应变化规律差异显著，体现出显著的“断层上盘效应”，因此，强震作用下近断层桥梁桩基础抗震设计时，应着重考虑断层上盘桩基础的抗震承载能力。

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.