碎石垫层沉箱基础水平循环加载模型试验与分析

Model tests and analyses of caisson foundation based on gravel cushion under cyclic lateral loads

碎石垫层沉箱基础是一种适于强震区深厚软弱土地基的深水基础形式,具有抗震性能良好、承载力高、便于施工、造价合理等优点。采用自主设计的大周数水平循环加载装置对碎石垫层沉箱基础开展了室内1g模型试验研究,探讨了基础在水平静力加载、循环加载以及循环后静力加载下的承载变形特性。试验研究表明,基础在长期水平循环荷载作用下具有安全可靠的工作性能。静载下基础的荷载–水平位移关系可视为刚塑性、滑动破坏前为双曲线关系。循环荷载下基础的累积位移发展呈现收敛的趋势,并随着荷载幅值的增大而增大;基础在单向循环荷载下的累积位移大于同等大小荷载静载下的位移。循环加载后基础沿各方向的水平承载力和刚度均有所提高。然后,对基于边界面理论的修正G-M弹塑性接触面本构模型进行改进,利用ABAQUS接触面子程序UINTER将其嵌入ABAQUS中,对碎石垫层沉箱基础的模型试验进行了有限元数值分析,模拟得到的规律与试验结果相近。

The caisson foundation based on the gravel cushion is a scheme of deep foundations suitable for the ground with thick weak soil in seismic areas and has many advantages such as excellent seismic resistance, high bearing capacity, convenience for construction and reasonable cost. In this study, a series of 1 g model tests on the caisson foundation based on the gravel cushion are conducted using a loading device designed for cyclic loadings of large cycle numbers, and the characteristics of bearing capacity and displacement of the foundation subjected to lateral static loads, cyclic loads and static loads after cyclic loadings are discussed. The experimental results reveal that the foundation has reliable working performance under long-term lateral cyclic loads. Under the static loading, the load-horizontal displacement curve of the foundation can be viewed as a rigid-plastic relation and described in a hyperbola relationship. Under the cyclic loads, the accumulative displacement of the foundation develops in a stable manner and increases with the amplitude of the cyclic loads. The accumulative displacement under one-way cyclic loads is larger than the displacement under the static loads with the same amplitude. Both the bearing capacity and loading stiffness are enhanced in all directions after cyclic loadings. Then the modified G-M elastoplastic interface constitutive model based on the boundary surface theory is improved and programmed into ABAQUS utilizing the interface user subroutine UINTER in ABAQUS, and the FEM analyses of model tests are conducted, and the results match well with the test ones.