Seismic Analysis of Pile Foundations Damaged in the January 17, 1995 South-Hyogo Earthquake by Using the Seismic Deformation Method

With respect to the South-Hyogo Earthquake of January 17, 1995, a lot of research results have been published including many studies on the damage to pile foundations resulting from liquefaction as well as consequent lateral flow of surface ground (Mori et al, 2000 and Horikoshi et al, 2000). However, reports concerning seismic analyses of foundations damaged by non-liquefaction causes, such as ground shaking, are still rare. Actually, studies on non-liquefaction damage are also important because this kind of damage may occur in a more extensive scope than the liquefaction damage may. This paper summarizes a seismic analysis of a pile foundation damaged by ground shaking induced by the quake. The method used for the analysis is so-called Seismic Deformation Method (SDM) that is stipulated in a new design code called Seismic Design Code for Railway Structures (the Railway Code, 1999, in Japanese). The seismic analysis was conducted in the procedure as: a) response analysis of the damaged pile foundation; b) assessing seismic performance of the foundation; c) comparison of the results obtained from the analysis and the in-situ damage investigation. As the results, the adequacy of SDM was confirmed by the good agreement between the analysis and investigation. Moreover, the damage mechanism of the foundation was elucidated based on the data from analysis and investigatio

In-situ horizontal cyclic loading tests on composite foundation composed of soilbags and piles

The authors have been developing a new composite foundation composed of piles and soilbags. The foundation is characterized by the laying of soilbags between the pile heads and the footing on which a superstructure stands. The expected effect of the foundation is to cut off the fixed connection between the piles and the footing in order to reduce the bending moment of the piles and the response acceleration of the structure. In this study, in-situ horizontal cyclic loading tests were conducted on the proposed composite foundation with two piles to investigate the seismic response characteristics of the foundation at real scale. It was found from the tests that the horizontal force reached its peak due to the uplift of the footing during horizontal loading, and that larger hysteresis damping was obtained than that of spread foundations due to the hysteresis effect in the shear deformation of the soilbags. As for the sectional force of the piles and the vertical stress inside the soilbags, it was found that the axial force and bending moment of the piles concentrated on the pile on the front side in the loading direction, and that the vertical stresses inside the soilbags concentrated just above the pile head on the front side in the loading direction. Although residual horizontal displacement and settlement occurred due to the cyclic load, little damage to the soilbags was observed