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Seismically Induced Lateral Earth Pressures on Retaining Struc. & Basement Walls

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SEAOC Blue Book Article 09.10.010

Seismically Induced Lateral Earth Pressures on Retaining Structures and Basement Walls

Starting with the Loma Prieta Earthquake in 1989 there has been an increased awareness of the potential magnitude of strong ground motions produced by major tectonically active faults. An important consequence has been the gradual tightening of code requirements for the design of retaining structures suggesting that these structures should be designed to much higher levels of seismic loading than assumed in the past. However, case history data and data from recent experimental work show that the currently used methods are quite conservative and lead to excessively conservative designs in regions where design PGA exceeds 0.4g. Specifically, the experimental data from seismic centrifuge tests shows that the seismic earth pressure distribution for moderate size retaining structures, on the order of 6-7 m high, is triangular, increasing with depth. Moreover, there is no significant increase in seismic earth pressure between unbraced and braced structures with fixed base, while the loads on free standing cantilever structures are substantially lower owing to their ability to translate and rotate. The significance of the observed seismic earth pressure distributions is that the dynamic force can be applied at 1/3H, as is done for static loading, which substantially decreases the design level seismic moments on the structures.