Modeling of Seismic Wave Scattering on Pile Groups and Caissons

I. Po Lam, H. Law and C.T. Yang

MCEER-07-0017 | 09/17/2007 | 118 pages

Keywords: Seismic wave scattering.  Pile groups.  Caissons.  Foundations.  Seismic designs.  Retrofitting.  Long-span bridges.  Seismic loads.  Irregular foundation boundaries.  Nuclear power plants (NPP).  Systematic modeling.

Abstract: This report documents practical modeling procedures adopted in the bridge engineering community involving seismic designs and retrofits of long span bridges relative to the treatment of wave propagation problems. It also discusses wave scattering issues that arise from irregular foundation boundaries and affect the seismic loading of bridges, which is not explicitly considered in current design practice. The research developed a systematic procedure that allows geotechnical engineers to perform wave scattering problems in the time domain considering all elements of boundary issues to minimize wave reflection and refraction. The solutions obtained from the time domain approach were rigorously compared against a traditional frequency domain approach. The established time domain procedure was shown to address not only free field conditions but also foundation systems subjected to earthquake loadings. Once the time domain procedure was established, the work was extended to address pile group foundation and gravity caissons under dynamic loading conditions, to gain an understanding of how the scattering of seismic waves from the foundation system alters the near field ground motion transmitted to the superstructure. The effects of wave scattering can now be more easily included in future design procedures.