project overview
It is generally agreed that the lateral earth pressures on retaining structures increase during earthquakes and the magnitude of the seismically induced lateral earth pressure is a routine part of any design calculation for retaining structures and basement walls based on the seismicity of the site. The methods currently in use have evolved gradually starting with seminal Japanese work performed in the 1920’s.
Figure 1. Mononobe-Okabe Force Diagram
The current “state of the art” is based on a combination of small scale laboratory model testing and analytical solutions that produce some very surprising results. As long as the seismic loads are small, the magnitude of the computed forces is relatively small and does not substantially influence design. However, in areas subject to very strong ground motions, such as the SF Bay area, the magnitude of the computed forces using methods currently suggested in the literature is such that it significantly increased design loads. This is particularly significant when applied to older structures that were typically designed for much smaller magnitude of ground motions than are currently considered appropriate.
However, a review of case histories from recent major earthquakes does not indicate any major or minor problems with retaining walls and basement walls that were not specifically designed for strong ground motions. Thus, there is an apparent disconnect between the “state of the art” analytical understanding of the problem and the actual field performance. The objective of this research effort is to re-examine the question of the seismic performance of buried or partially buried structures in order to develop more effective and economic design guidelines that take into account the actual performance of these types of structures during earthquakes.
This research effort is jointly funded by the Bay Area Rapid Transit (BART) and Valley Transportation Authority (VTA).
