液化土层厚度差异下大直径变截面单桩基础振动台试验

Shaking table test of large diameter single pile foundation with variable section under different liquefied soil thicknesses

针对地震作用下不同液化土层厚度对大直径变截面单桩基础动力响应的影响,依托实体工程设计振动台模型试验,分别从土层孔压比、桩身加速度、桩顶水平位移及桩身弯矩等方面对大直径变截面单桩基础的动力响应进行了研究,结果表明:孔压比开始增长和趋于稳定的时间随液化土层厚度的增加均呈滞后趋势,液化土层厚度越薄,孔隙水上升越快,液化土层越容易发生液化。变截面位置位于液化土层时加速度增长较为明显,El-Centro波作用时大直径变截面单桩基础桩顶加速度放大系数最小,1004波作用时桩顶加速度放大系数最大;大直径变截面单桩基础桩顶水平位移最大值随液化土层厚度的增加逐渐增大,且地震波差异会影响其趋于最大值的时间;大直径变截面单桩基础最大弯矩在液化土层和非液化土层交界产生,且液化土层厚度越大地震波差异性对变截面位置处弯矩影响越大。在进行大直径变截面单桩基础的抗弯设计时,应着重考虑液化土层和非液化土层分界面处和变截面处抗弯能力。液化土层从30cm到50cm,大直径变截面单桩基础桩身加速度放大系数及桩顶位移分别增加了1.61倍和1.65倍。

Based on the results of the physical model test of the actual works design shaking table,the dynamic response of large diameter single pile foundation with variable section was analyzed from those aspects such as pore pressure ratio of soil layer,pile shaft accelera-tion,horizontal displacement of pile top and bending moment of pile shaft,after studying the influences of different liquefied soil layer thicknesses on the dynamic response of large diameter single pile foundation with variable section.The results show that:the time when the pore pressure ratio starts to increase and stabilize lags behind the increase in the thick-ness of the liquefied soil layer,and the thinner the liquefied soil layer,the faster the pore water rises and the easier the occurrence of liquefaction for the liquefied soil layer shall be.When the variable section position is located in the liquefied soil layer,the growth of ac-celeration is more obvious.For the El-Centro wave,the amplification factor of pile top accel-eration of large diameter single pile foundation with variable section is the minimum,and for the 1004 wave,the amplification factor of pile top acceleration is the maximum.The maxi-mum horizontal displacement of large diameter single pile foundation with variable section increases gradually with the increase of liquefied soil layer thickness,and seismic wave differences may affect the time corresponding to the maximum value;The maximum bending moment of large diameter single pile foundation with variable section occurs at the interface of liquefied soil layer and non-liquefied soil layer,and the greater the thickness of liquefied soil layer,the greater the influence of seismic wave difference on bending moment at varia-ble section position shall be.When designing large diameter single pile foundation with vari-able section for its bending resistance,attention should be paid to the bending resistances at the interface between the liquefied soil layer and the non-liquefied soil layer and at the vari-able section position.When the thickness of liquefied soil layer increases from 30cm to 50cm,the acceleration amplification factor of the large diameter single pile foundation with variable section and the displacement of the pile top may increase by 1.61 and 1.65 times,respectively.