In this paper, a new composite foundation composed of piles and soilbags is proposed, and its mechanical behavior is investigated systematically with numerical analyses based on sophisticated models for both soils and structures. The foundation is characterized by the laying of soilbags between the pile heads and the footing on which the superstructure stands. The expected effects of the foundation are to cut off the fixed junction between the piles and the footing in order to reduce the bending moment of the piles and decrease the response acceleration of the structure. In this study, the seismic response of the proposed composite foundation is investigated numerically by a 3D elastoplastic FEM analysis, and the superiority of the proposed composite foundation over the conventional pile foundation is discussed in detail. From the analysis, it is found that both the bending moment and the response acceleration of the pier are suppressed because of the elongation of the natural period of the foundation and the increase in the hysteresis damping of the soilbags. In addition to the above-mentioned effect on the response acceleration, the bending moment of the piles is greatly reduced at the pile heads in the proposed composite foundation due to the effect of the stress dispersion of the soilbags.

在本文中，提出了一种由桩和土袋组成的新型复合地基，并基于复杂的土壤和结构模型，通过数值分析系统地研究了其力学行为。基础的特点是在桩头和上部结构所在的基础之间铺设土袋。基础的预期作用是切断桩与基础之间的固定连接处，以减少桩的弯矩，降低结构的响应加速度。在这项研究中，提出的复合地基的地震响应通过 3D 弹塑性有限元分析进行数值研究，并详细讨论了提出的复合地基相对于传统桩基的优越性。从分析来看，研究发现，由于地基自然周期的延长和土袋滞回阻尼的增加，桥墩的弯矩和响应加速度均受到抑制。除了上述对响应加速度的影响外，由于土袋应力分散的影响，拟议的复合地基中桩头处的桩弯矩大大降低。