| Popis: |
Observations of the performance of basement walls and retaining structures in recent earthquakes show that failures of basement or deep excavation walls in earthquakes are rare even if the structures were not designed for the actual magnitude of the earthquake loading. For instance, no significant damage or failures of retaining structures occurred in the recent earthquakes such as Wenchuan earthquake in China (2008) and, or subduction zone generated earthquakes in Chile (2010) and Japan (2011). In order to develop a better understanding of the distribution and magnitude of seismic earth pressures on cantilever retaining structures series of centrifuge experiments was performed on model retaining and basement structures with cohesionless and cohesive backfill. Results obtained from the centrifuge experiments were subsequently used to develop and calibrate a two-dimensional, nonlinear, finite difference model built on the FLAC platform. The purpose of this paper is to provide a general overview of the research program and its results. In general, the centrifuge data consistently showed that for the height of structures considered herein, i.e. in the range of 20-30 ft, the maximum dynamic earth pressure increases with depth and can be reasonably approximated by a triangular distribution This suggests that the point of application of the resultant force of the dynamic earth pressure increment is approximately 1/3H above the base of the wall as opposed to 0.5-0.6 H recommended by most current design procedures. In the present study, experimental data suggest that seismic loads up to 0.4 g could be resisted by cantilever walls designed to an adequate factor of safety. The numerical models using FLAC finite difference code were quite successful and able to produce a reasonably good agreement with the results of the centrifuge experiments. However, while the finite difference models were able to capture the main aspects of the seismic response observed in the centrifuge experiments, the results of the analyses were highly sensitive to the selection of soil and interface parameters. Therefore, numerical models used for future designs should be carefully calibrated against experimental data in order to provide reliable results. |
