地震作用软土震陷特性及变截面群桩动力响应

Seismic Subsidence Characteristics of Soft Soil and Dynamic Response of Pile Group with Variable Cross Section

为研究不同类型地震波作用时软土场地条件下大直径变截面群桩基础的动力响应特性,依托翔安大桥实体工程,通过振动台试验,选取地震动强度均为0.15g的人工合成5010波、1004波,以及Kobe波和El-Centro波,研究了群桩基础桩周土层震陷量、桩身加速度、桩顶水平位移、桩身弯矩等动力响应特性.结果表明:地震作用下,软土层发生震陷,震陷量为0.16~0.22cm,其值与输入地震波的频谱特性有关;桩端加速度时程响应曲线较桩顶及变截面处更为“密集”;软土对加速度产生放大效果,输入地震波加速度峰值出现时刻均早于桩端、桩顶及变截面处;桩身加速度及桩顶水平位移分别在1004波和Kobe波作用下达到最大值;5010波和1004波作用下,桩顶产生永久侧向位移;Kobe波作用下,桩身弯矩峰值最大,且弯矩峰值出现时刻最晚.因此,在进行群桩基础抗震设计时,针对不同桩基特性可选用不同类型地震波进行验算.

To study the dynamic response characteristics of large-diameter variable cross-section pile group foundations under different types of seismic waves in soft soil site conditions,the shaking table test was carried out based on the solid project of Xiang-An Bridge.The synthetic 5010 and 1004,Kobe,and El-Centro waves with a ground motion intensity of 0.15g were selected in the test.The dynamic response characteristics of the pile group foundation,such as the seismic settlement of soil around the pile,acceleration of the pile body,horizontal displacement of the pile top,and bending moment of the pile body,are studied experimentally.The test results show that under the action of the earthquake,the soft soil layer has seismic subsidence,and the amount of seismic subsidence is in the range of 0.16~0.22 cm,which is related to the spectral characteristics of the input seismic wave.The acceleration time history response curve of the pile end is more“dense”,and the soft soil has an amplification effect on the acceleration.The peak acceleration of the input seismic wave appears earlier than the pile end,the pile top,and the variable section.The acceleration of the pile and the horizontal displacement of the pile top reach the maximum under the action of the 1004 wave and Kobe wave,respectively.Under the 5010 and 1004 waves,the pile top produces permanent lateral displacement.Under the Kobe wave,the peak bending moment of the pile is the largest,and the peak bending moment appears the latest.Therefore,in the seismic design of pile group foundations,different seismic wave types can be selected for different pile foundation characteristics.