Redundancy that helped a wall survive an extremely high seismic load

This photo shows a geosynthetic-reinforced soil wall that survived a substantially higher seismic load than its designed seismic load. This resulted from redundancy due to use of soil design Φ value lower than its actual value. Furthermore, the substantial apparent cohesion and toe resistance were also ignored.

Such a wall serves as a lifeline and its earthquake survival is critical. Note that survival of this type of MSE wall does not imply that all MSE walls would have equally survived. In fact, during the 2011 Great East Japan Earthquake, although all walls of the same type as the one shown in this photo were seismic-designed for a/g> 0.4 and performed very well, at least two different types of walls failed in ultimate state mode under seismicity of about a/g=0.30. These walls are exempt from seismic design per AASHTO, yet their existing static redundancy was insufficient.