Seismic performance of a building affected by moderate liquefaction during the Christchurch earthquake

Abstract

The seismic performance of an important structure in Christchurch, New Zealand was well-documented during the 2010–2011 Canterbury earthquake sequence. Minor ground deformation and negligible-to-minor structural damage occurred during the primary events of the sequence, except for the 22 February 2011Mw6.2 Christchurch earthquake, which produced differential movement of the basement mat and architectural and structural damage. This case history is evaluated to garner insights. Static settlements are estimated to establish the pre-seismic conditions of the building. Dynamic nonlinear effective stress soil-structure-interaction analysis are performed for the primary events of the Canterbury earthquake sequence using FLAC2D with the PM4Sand constitutive model to capture the cyclic response of the key soil units. The analytical results indicate the post-Canterbury earthquake sequence measured differential mat movements were primarily due to the earthquake events. A thin liquefiable layer, which historic maps indicate is now a buried stream deposit, is largely responsible for the ground movements. A medium dense sandy gravel also appeared to contribute significantly to the observed foundation movements.