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

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 1g 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.