地震作用下高承台群桩基础振动台试验研究

Experimental study on seismic response of pile group foundation with high-cap by shaking table

针对震害特征明显、承受水平荷载不利的高承台群桩基础,以埋入式低承台群桩基础作为比较对象,开展砂质粉土地基条件下高、低承台群桩基础模型体系的振动台试验,详细分析试验体系的加速度响应、桩身内力、土-结构接触动土压力等响应特征。试验结果表明:采用的均匀砂质粉土地基主要起放大作用,地基土与桩身的加速度响应自下而上被逐渐放大;高承台桩体系由于承台与桩身外露,使得辐射阻尼耗散能量的作用减弱,导致高承台桩结构体系的动力响应显著,而低承台桩基由于埋入式承台结构受到较强的土体约束作用,造成其加速度响应较小;桩顶与承台联结的嵌固效应、承台与桩身自由段的外露(桩周侧向无地基土约束),将会显著改变桩身的内力分布;同时也观测到埋入式承台结构的正侧面动土压力显著发挥,反映了在承台、基桩和地基土协同工作中承台侧面水平抗力的贡献不容忽视。试验揭示了地震作用下高承台桩基础的动力响应规律,为桩基础的抗震设计提供参考。

In view of the high-cap group piles with obvious seismic damage characteristics and unfavorable bearing horizontal load,the shaking table test for the model system of high-cap and low-cap group piles foundation under sandy silt soil was carried out,and the response characteristics of the test system,such as acceleration response,internal force of pile body and soil-structure contact dynamic earth pressure,were analyzed in detail.The test results show that the uniform soil mainly plays an amplifying role,and the acceleration response of soil and free section of pile body is gradually enlarged from bottom to top;the radiation damping dissipation energy is weakened due to the exposure of pile cap and pile body in high-pile system,resulting in significant dynamic response of high-pile structural system,while the low-cap pile foundation is subjected to strong soil body due to the embedded cap.The embedding effect of the connection between pile top and pile cap,the exposure of pile cap and free section of pile body(without foundation soil constraints in the lateral direction of pile),will significantly change the internal force distribution of pile body;at the same time,it is observed that the dynamic earth pressure on the front side of the embedded cap structure plays a significant role in the collaborative work of cap,foundation pile and foundation soil.The test reveals the law of dynamic response of pile foundation with high cap under earthquake action,which provides reference for seismic design of pile.