Numerical analyses and shaking table tests on seismic performance of existing group-pile foundation enhanced with partial-ground-improvement method

抄録

In soft ground, pile foundation is commonly used for heavy superstructures. Earthquake is a natural phenomenon that threatens the superstructures with pile foundation. Statistical data from past-experienced earthquakes like 1995 Hyogoken-Nanbu earthquake shows that the failure of pile foundation during a major earthquake happened frequently. Therefore, it is necessary to investigate the mechanical behavior of pile foundations at the ultimate state during a major earthquake and enhance its seismic behavior. An economical and effective method for improving the seismic performance of an existing pile foundation is partial-ground-improvement method. In this method, determining the size and the location of the improving area around the pile foundation is an important matter and it needs to be clarified. In some cases in spite of the partial-ground-improvement has been conducted, but there is less upgrading in the seismic behavior. In this paper, in order to find an optimum pattern for the partial-ground-improvement method, numerical analyses and 1g shaking table tests are conducted. In the numerical analyses and shaking table tests a soil-pile foundation-superstructure system is adopted. Consequently, the seismic behavior of an elevated bridge supported by group-pile foundation with three different patterns of partial-ground-improvement and one other pattern without partial-ground-improvement is investigated. Finally, an optimum pattern for the partial-ground-improvement method is proposed that can reduce the influence of earthquake on pile foundations. In the numerical analysis, 3D soil-water coupling elastoplastic dynamic finite element method with a program called DBLEAVS (Ye et al., 2007) is used. In order to numerical analyze the seismic behavior of the pile foundation, multiple factors like the soil properties, the pile foundation, the superstructure and the mutual interaction between these factors should be taken into consideration. Therefore, in present study the soil, the group-pile foundation and the superstructure are modeled with proper constitutive model.