Evaluation of Liquefaction Ejecta Case Histories in Christchurch

Liquefaction ejecta were a key mechanism of liquefaction-induced land damage and residential house damage during the 2010-2011 Canterbury earthquake sequence. To gain insight, 244 well-documented liquefaction ejecta case histories of ejecta occurrence, its quantity, and its effects on infrastructure were developed. The authors take advantage of a comprehensive dataset of thousands of CPTs and boreholes, LiDAR surveys, aerial photographs, ground surveys, and liquefaction land damage documentation from insurance claims. The ejecta database includes 61 sites that underwent four major earthquakes that produced varying degrees of liquefaction-induced land damage ranging from no ejecta to extreme ejecta. Liquefaction ejecta coverage and amounts for each of the four primary earthquakes of the Canterbury sequence were extracted using both LiDAR-based and photographs-based approaches because direct measurements of the ejecta-induced settlement were not available. The ground conditions and seismic demand leading to the differing quantities of ejecta-induced settlement during the Canterbury earthquakes were characterized. The database will hopefully lead to the development of methods that estimate the likelihood of liquefaction ejecta and the amount of ejecta-induced ground settlement at a site.