Comparison between predicted liquefaction induced settlement and ground damage observed from the Canterbury earthquake sequence

This paper reviews predictions of ground settlement due to post-liquefaction volumetric consolidation, and compares these predictions to ground damage observed from the Canterbury Earthquake Sequence in selected areas of Christchurch with differing ground conditions.

While ground settlement due to volumetric consolidation is only one component of the many liquefaction-related phenomena which can result in ground damage, it is one of the few aspects of post-liquefaction behaviour where simple predictive correlations are currently available to estimate consequential ground damage. So while predicted volumetric consolidation settlements do not capture all aspects of liquefaction-induced ground damage, they can provide a useful index for engineering practitioners to help compare potential ground damage at different sites.

This paper seeks to assist practitioners in their use of settlement predictions as an index of damage by examining how site-specific ground conditions can alter the consequential ground damage from liquefaction. Six sites across Christchurch are examined, two where analysis of CPT data predicts minor volumetric consolidation settlement, two where moderate settlements are predicted, and two where significant settlements are predicted. For one site from each pair, observations of ground damage from the Canterbury Earthquake Sequence are in general agreement with the settlement prediction. For the other site from each pair, observed ground damage was significantly less than would be suggested by the settlement prediction. The reasons for this difference between predicted and observed behaviour are investigated. Factors that are examined include the effect of sand boils, lateral spreading, crust thickness and strength, depth at which liquefaction occurs, and layered soil profiles.