【目的】为解决刚性连接桩承台与桩头节点处较容易破坏的问题。在土工箱内开展单桩模型试验,研究桩头与承台连接处设置加强环、“桩伴侣”以及连接墙前后的抗震性能。【方法】在此基础上以实际输电线路基础工程2×2低承台PHC弹性中长群桩为背景,进一步阐述上述变刚度构造增强机理,并通过有限元方法研究上述群桩形式下桩头设置变刚度构造前后水平承载特性。【结果】结果表明:桩头外部设置变刚度构造通过扩大桩头截面和提高桩头抗弯刚度、大幅减小桩顶负弯矩来提高桩顶抗震与水平承载性能。在水平荷载施加至1.6Hu(3200kN)时,桩头外部设置变刚度构造能提高桩顶水平承载力27.50%~29.92%。同时增大桩周土体的工作范围,使地基土的水平变形减小22.1%~26.53%。圆形套筒和连接墙可以在任何土质情况下发挥作用,实际工程需综合考虑变刚度构造高、厚径比限值,避免建筑材料浪费。

【Purposes】To solve the problem that the joint between rigid connection pile cap and  pile head is easy to be damaged, single pile model tests are carried out in a geotechnical box to study  the seismic performances of the connection between pile head and pile cap, “pile companion”, and  connection wall. 【Methods】 On this basis, based on the actual transmission line foundation project  2×2 low-cap PHC elastic medium-long pile group was adopted to further elaborate, the above- mentioned variable stiffness structure enhancement mechanism, and the finite element method was  used to study the horizontal bearing characteristics of the pile head before and after the setting of vari⁃ able stiffness structure in the pile group. 【Findings】The results show that the variable stiffness struc⁃ ture outside the pile head can improve the seismic and horizontal bearing capacities of the pile top by  expanding the cross section of the pile head, improving the bending stiffness of the pile head, and  greatly reducing the negative bending moment of the pile top. When the horizontal load is applied to  1.6H =3 200 kN, the variable stiffness structure outside the pile head can improve the horizontal bear⁃ ing capacity of the pile top by 27.50%~29.92%. At the same time, the working range of the soil  around the pile is increased, and the horizontal deformation of the foundation soil is reduced by  22.1%~26.53%. The circular sleeve and connecting wall can play a role in any soil condition. In prac⁃ tical engineering, it is necessary to comprehensively consider the limit heigth and thickness-to- diameter ratio of variable stiffness structure to avoid the waste of building materials.