可液化场地桥梁群桩基础地震响应振动台试验研究

Shaking table test on seismic response of pile groups of bridges in liquefiable ground

针对上覆黏土层、下部饱和砂层结构的可液化场地条件,采用2×2低承台群桩—独柱墩结构,完成了可液化场地群桩–土–桥梁结构地震相互作用振动台试验。试验表明:在小幅震动阶段孔压仅有少量积累,孔压积累主要发生在强烈振动段;孔压随震动幅值增大、持时延长而变得更高;最强烈液化作用滞后于峰值加速度时刻。砂层加速度反应受场地液化影响较大;随着砂层液化的发展,土层位移峰值时刻与输入地震波峰值时刻、土层加速度峰值时刻之间表现出明显的时滞特征,而土层位移对桩的弯矩反应起着越来越明显的作用,且液化砂层位移对桩土相互作用力影响效应已凸显;完全液化砂层的承载力并未全部丧失;无论砂层液化与否,桩与砂层加速度反应规律保持一致;地震中土层分界附近桩的加速度、弯矩出现突变。振动台试验无疑为可液化场地桥梁群桩抗震性能研究提供必要铺垫。

Shaking table test on seismic low-cap pile groups-soil-bridge structure interaction in liquefiable ground with the overlying clay layer and the lower saturated sand layer is completed.The test indicates that pore pressure caused by the slight vibration during earthquake is only a small amount of accumulation,and pore pressure accumulation mainly occurs at the stage of strong vibration.The pore pressure gradually increases as the input motion amplitude becomes larger and the shaking duration becomes longer.It’s obtained that the strongest liquefaction lags behind the peak acceleration time.Acceleration of the sand is remarkably influenced by soil liquefaction.With the development of soil liquefaction,the time-delay characteristics between the peak soil displacement time and the peak input motion time,and the peak acceleration time of soil are significantly displayed,and soil displacement plays an increasingly prominent role in the bending moment of the pile.Similarly,the displacement of liquefied sand has a specially obvious effect on pile-soil interaction.The fully liquefied sand doesn’t completely lose the bearing capacity.Whether the sand is liquefied or not,the acceleration law of the pile and the sand maintains consistent.During the earthquake,the jump reaction of the acceleration and the bending moment on the pile is observed near the soil interface.It’s no doubt that the shaking table test provides the necessary groundwork to study seismic performance of pile groups of bridges.