Soil structure interaction in laterally displacing ground

Abstract

Design or assessment of structures founded on ground with a potential for seismic induced ground displacements requires careful consideration of the associated soil structure interaction (SSI). These seismic ground displacements could be due to liquefaction and cyclic displacement or lateral spread, or due to slope instability. Potential ground movement and SSI includes considerable uncertainty. This paper outlines some SSI principles to be considered to allow for this uncertainty. Three case studies describe application of these principles. These principles include developing possible scenarios of ground movement, ground and structure shaking and SSI, and testing the design relative to these scenarios. Relative stiffness of ground and structural elements needs to be considered in developing these scenarios. Is the structure pushing the ground or is the ground pushing the structure? The impact of SSI on the magnitude of ground displacement needs to be considered. Will the SSI arrest the ground movement or will the ground movement potentially pull the structure apart? The presented principles and case studies focus on qualitative and simplified numerical assessments. Where considered appropriate and necessary, higher level analyses including dynamic finite element modelling could be undertaken. These higher level analyses should be to supplement rather than replace the simplified methods described in this paper. Higher level analyses could be particularly useful in understanding possible mechanisms of SSI. Assessment would require engineering judgement considering all available information.