3D dynamic finite element analyses and 1Â g shaking table tests on seismic performance of existing group-pile foundation in partially improved grounds under dry condition

Pile foundations are commonly used for heavy superstructures in soft grounds. The failures of pile foundations have been reported in past major earthquakes. An economical and effective method for improving the seismic performance of existing pile foundations is the partial-ground-improvement method (PGI). The main concern of this method is how to determine the size and the location of the areas around a pile foundation to be improved. In this paper, numerical analyses and shaking table tests are conducted to find the optimum pattern for the PGI method. In the numerical analysis, the three-dimensional (3D) dynamic finite element method (FEM) is used with a unified system consisting of a ground, a group-pile foundation and a superstructure. Furthermore, the mechanical behaviors of the ground, the group-pile foundation and the superstructure are modeled by the Cyclic Mobility model, the axial force-dependent model, and the tri-linear model, respectively. With the above-mentioned numerical method, four different patterns of PGI are investigated and then an optimum pattern for the PGI method is proposed. All the numerical analyses are also confirmed by 1 g shaking table tests. All the tests and the numerical analyses are conducted under dry condition.