This project addresses the lessons learned from the 17 October 1989 Northern California (Loma Prieta) earthquake. It addresses the seismic performance of tieback retaining walls. Tieback retaining walls are commonly used for the temporary support of excavations for building construction. These types of support systems are typically designed on the basis of empirical experience with little, if any, thought given to seismic design requirements. Questions regarding the seismic performance of these types of structures are becoming more important with the increasing use of these walls for the permanent support of excavation cuts. While earthquake-related failures of tieback walls have not been reported in the literature, it is not clear if this fortunate circumstance is due to a conservative (but expensive) design practice, or to the limited number of cases where these types of walls have been subjected to earthquake ground motions. The aim of this project is to enhance the current state-of-the-art in the seismic design of tieback retaining walls by reviewing the performance of existing walls - both temporary and permanent - in the San Francisco Bay area that were subjected to the ground shaking from the Loma Prieta earthquake. Particular emphasis is given to tieback walls constructed with the "soil nailing" technique, which is relatively new in the United States. Available information on the horizontal displacement of the walls and/or load increases in the tiebacks within the walls, and on any damage experienced, is studied; these data are compared to the general design practice for these types of walls. The benefit of this research is that it will improve the state of the engineering practice in the design of permanent tieback walls. This should facilitate the widespread use of tieback retaining walls in areas of high seismicity, leading to a safer and more economical design.
