土–桩基–核岛体系动力相互作用振动台试验及数值模拟

利用振动台试验研究了土–桩基–核岛体系动力反应规律,分析了桩身内力分布特征、变形规律和桩身破坏模式。试验结果表明:输入不同幅值的地震动时土层与桩基础结构均出现加速度放大情况,其中远离结构自由场放大系数峰值出现土层表面,桩间土层放大系数峰值出现在土层中部,表明桩基础对土层加速度放大情况有一定影响;桩身在中部出现加速度放大峰值后在靠近承台位置出现减小,表明上部结构对桩身加速度放大分布有显著影响。桩身剪力在桩-承台连接处最大并随深度增加而减小,弯矩在桩顶部及中上部位置较大。桩-承台连接处、桩中部(约6倍桩径)为桩身薄弱环节,破坏形式为拉伸剪切破坏及弯曲破坏。群桩各桩的破坏顺序为沿振动方向一侧边桩先出现破坏并引起中部角桩破坏,后中桩破坏,另一侧边桩最后破坏。水平地震荷载作用下群桩的可能破坏机制是沿振动方向的边桩由于受桩周土的约束较弱、最先受到地震的作用,更容易先发生破坏,并引起其它位置的桩发生破坏。

Shaking table tests and numerical simulations of dynamic interaction of soil-pile-nuclear island system

The dynamic response characteristics of soil-pile-nuclear island system are studied through the shaking table tests.The distribution pattern of internal force,deformation mode and failure mechanism of piles are analyzed.The test results show that when the RG160 artificial waves of different amplitudes are input,acceleration amplification occurs in both the soil layer and the pile foundation structure.The peak value of the amplification coefficient of the free field far away from the structure appears on the soil surface,while the peak value of the amplification coefficient of the soil layers between piles appears in the middle part,which indicates that the pile foundation has a certain influence on the acceleration amplification of the soil layers.The peak value of the amplification coefficient along pile appears in the middle part and then decreases near the pile cap indicating that the superstructure has a significant effect on the acceleration amplification distribution along the piles.The shear force of pile body is the maximum at the pile-cap connection and decreases with the increase of depth,while the bending moment is larger at the top and middle upper positions of the piles.The pile-cap joint and the middle part of the piles(about 6 times the diameter of the piles) are the weak point of the piles,and the failure modes are tensile shear failure and bending failure.The failure sequence of the pile groups is that the piles at one side along the vibration direction are damaged first and cause the failure of the middle corner piles,then the middle piles are damaged,and the piles at the other side are destroyed finally.The possible failure mechanism of the pile groups under horizontal seismic loads is that the piles at one side along the vibration direction are more likely to be affected and damaged first by the earthquake because of the weak constraint of the around soils,and then cause the destruction of other piles.The conclusion can provide reference for the seismic design of pile foundation of nuclear island plants.