可液化场地桩基桥梁结构地震响应振动台试验

实施了可液化场地桩-土-桥梁结构地震相互作用振动台试验,研究桩基桥梁结构地震响应特征.试验再现了自然地震触发场地液化与结构破坏的主要宏观现象.小震输入下,地基动力反应较小,孔压在输入波峰值到达后几秒内达到峰值,并很快进入消散阶段,近桩区与远桩区峰值孔压差别很小,砂层上部轻微液化;桩-柱墩表现为弹性动力变形,地基对桩地震反应约束效应较大,桩在砂层中动应变大于粘土层中动应变;由于上覆粘土层对桩的嵌固与墩顶配重惯性力的共同作用,致使桩在上覆粘土层中动应变远大于柱墩动应变.大震输入下,砂层很快全部液化且发生强烈剪切流动,孔压在输入波峰值到达瞬间增大,而后缓慢上升至峰值,消散也很慢,近桩区峰值孔压远大于远桩区峰值孔压;墩顶配重产生较大惯性力作用,加之砂层全部强烈液化使得桩-柱墩动力反应十分强烈,导致桩上部嵌固点发生大幅度上移,且在砂层与上覆粘土层过渡带附近出现大范围破裂、在粘土层中折断.

Shake table test for seismic response of pile foundation and bridge structure in liquefiable ground

The shake table test for studying the pile-soil-structure seismic interaction in liquefiable ground was carried out,and the characteristics of seismic response of the structure were investigated.Results show that under small seismic input,the dynamic response of foundation is relatively small,while the pore pressure reaches its peak within several seconds after the peak input acceleration time and then,almost immediately,begins to dissipate.Slight liquefaction occurs in the upper sand layer,and the difference of peak pore pressure between far-pile area and near-pile area is very little.The dynamic deformation of pile-pier manifests specific elasticity,and the confinement effect of foundation on the seismic response of the pile cannot be neglected.The dynamic strain of pile in sand is larger than that in clay.On the other hand,the dynamic strain of pile in clay is much larger than that of pier,due to the co-action of confinement effect of upper clay on the pile and counterweight inertia effect of the pier top.While inputting the large seismic wave,complete liquefaction,accompanied by strong shear flow,occurs in a short time.The pore pressure increases immediately after the peak input acceleration time,then increases to its peak gradually,and the dissipation rate is also very low.The peak pore pressure of near-pile area,different from the case of small seismic input,is much larger than that of far-pile area.Dynamic response of pile-pier is quite violent,and the fixing point of pile greatly moves upwards,as a result of large counterweight inertia effect together with complete liquefaction in sand.A large range of damage locates around the interface of sand and upper clay layers,and the pile breaks in the clay layer.