9714859 Lee Most large metropolitan areas here in the United States, or countries in other parts of the world, already have or are planning to have underground infrastructure systems as an alternate way of urban transportation. It is important to understand the characteristics of damages associated with the underground construction and to find out the cause of both geotechnical as well as structural deformations, and also, to study the influence of local site effects in the vicinity of the structure on the amplification of structural deformations resulting from strong earthquake motions. Experiences from previous earthquakes suggest that the recorded motions in some areas had larger than expected amplitudes. These are usually areas with large depths of alluvial sediments together with comparatively soft soil deposits near the surfaces. Massive civil infrastructures (dams, freeway networks, bridges and now the underground subways) respond to strong earthquake ground motions that are highly dependent on the surface and subsurface topographies at the local sites. This project is to study the effects of the interactions among the subways, the multiple structural foundations and the local geology, to explore how all these key elements will affect the resulting amplifications of foundation motions. The proposed method is based on the wave propagation in elastic solid media. The challenge in solving the problem will be in the boundary conditions where the nonorthogonal compressional and shear potentials are coupled. This will be overcome with expanded series and integral representations of the wave potentials. Results from these studies will be compared with the actual deformations as recorded from previous earthquakes. The comparisons will serve as guidelines to the correct modelling of the problem under consideration. With proper understanding of how surface (buildings and freeways) and subsurface (underground subways) structures performed during str ong-motion earthquakes, future structural design of new buildings and retrofit plans for existing structures can be improved by including these local site effects to provide the correct design strength and reinforcement. Then it will help to minimize property damage and the loss of life in future earthquakes to come. ***
