Geotechnical design with apparent seismic safety factors well-bellow 1

•Foundation and slope seismic design can be safe even with apparent factors of safety well below 1.•Foundation uplifting and bearing capacity mobilization can lead to improved seismic performance of superstructure.•Maximum and residual settlement and rotation must be properly faced in the design.

The paper demonstrates that whereas often in seismic geotechnical design it is not realistically feasible to design with ample factor of safety against failure as is done in static design, an “engineering” apparent seismic factor of safety less than 1 does not imply failure. Examples from slope stability and foundation rocking illustrate the concept. It is also shown that in many cases it may be beneficial to under-design the foundation by accepting substantial uplifting and/or full mobilization of bearing capacity failure mechanisms.