扩孔隔震桩-土相互作用受力性能拟静力试验

Quasi-static Test on Mechanical Behaviors of Pre-hole Isolation Pile-soil Interaction

整体桥上部结构在温度及地震作用下所产生的纵桥向变形极易导致混凝土桩的顶部区域发生破坏。扩孔并填充阻尼材料可形成扩孔隔震桩,提高整体桥中混凝土桩的抗震性能。以某整体桥的桥台下单桩为工程背景,考虑不同扩孔直径和阻尼填料(橡胶颗粒和泡沫),开展扩孔隔震桩-土相互作用受力性能拟静力试验研究。研究发现:达到最大荷载时,无扩孔试件出现桩-砂土分离现象;当扩孔直径为2倍桩径时,试件出现桩-阻尼填料和阻尼填料-砂土分离现象,当扩孔直径为3倍桩径时,填充橡胶颗粒的试件的桩身水平位移完全被橡胶颗粒所吸收。故扩孔直径是影响桩身水平位移在阻尼填料中传递方式的关键参数;与无扩孔试件相比,扩孔隔震试件的滞回曲线更加饱满且等效黏滞阻尼比更大,可以发挥阻尼材料的耗能特性;填充橡胶颗粒的耗能效果优于填充泡沫,这是因为松散橡胶颗粒的变形能力和自动复位特性有利于能量耗散,而泡沫的整体性使其黏滞性和减震性不能完全发挥;在扩孔深度范围内,扩孔隔震试件的p-y曲线刚度明显低于无扩孔试件(最大降幅达到45.1%);随着扩孔直径增大或阻尼材料刚度减小,地基土模量系数减小;与无扩孔试件相比,扩孔隔震试件最大荷载略大,初始刚度和桩身最大弯矩略小。

The heads of reinforced concrete(RC)piles are extremely easily damaged owing to the longitudinal deformations induced by the superstructures in integral abutment bridges(IABs)under temperature variations and seismic actions.The pre-hole isolation piles can be obtained by predrilling oversized holes(pre-holes)filled with damping materials.This can improve the seismic performance of RC piles in IABs.A pile beneath an abutment in an IAB was chosen as a case study.Quasi-static tests considering different pre-hole diameters and damping materials(rubber particles and foam)were carried out to analyze the mechanical behaviors of pre-hole isolation pile-soil interaction.When the loads reached the peak values,pile-sand separation was observed in the specimen without a pre-holes.Pile-damping material and damping material-sand separations were found in the specimens when the pre-holes diameter was two times the pile diameter.The horizontal displacement of the pile was completely absorbed by the deformation of rubber particles in the specimen with a pre-holes filled by rubber particles when the pre-holes diameter was three times the pile diameter.Therefore,the pre-holes diameter can be considered the parameter with the most influence on the transmission mode of pile horizontal displacement to the damping materials.Compared with the specimen without a pre-holes,the hysteresis loops of the pre-holes isolation specimens were larger,as were the equivalent viscous damping ratios.It can be concluded that the energy of the damping materials can be dissipated in the pre-holes isolation piles.The energy dissipation of the specimen with a pre-holes filled by rubber particles is stronger than that of one filled by foam.This is because the deformation capacity and automatic reset characteristics of the loose rubber particles can help energy dissipation;however,the viscosity and damping characteristics of the foam are influenced by its integrity.The stiffness of the p-y curves of the pre-holes isolation specimens within the pre-holes depth were significantly lower than those of the specimen without a pre-holes(maximum decrement of 45.1%).With an increase in the pre-holes diameter or a decrease in the stiffness of the damping materials,the soil modulus coefficients decrease.Compared with the specimen without a pre-holes,the ultimate load-bearing capacities of the pre-holes isolation specimens were slightly larger,and the initial stiffness and maximum bending moments along the piles were slightly smaller.