Effects of Liquefaction on Structures in Christchurch

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Conventional liquefaction evaluation procedures cannot explain the different levels of liquefaction-induced building damage that occurred in Christchurch, New Zealand during the 2010-2011 Canterbury earthquake sequence. Each event with its different effects on structures warrants further study. Performance based earthquake engineering requires robust analytical tools that can discern varying levels of seismic performance. The 2010-2011 Canterbury earthquake sequence, with its excellent recordings of ground motions, its comprehensive subsurface investigation program, and its well-documented performance of structures in Christchurch, provides an exceptional opportunity to advance liquefaction evaluation tools. With the limitations inherent in investigating liquefaction effects solely in the laboratory or through numerical simulations, there is a pressing need to use these well-documented case histories to gain insights and to develop improved analytical procedures. The quantity and quality of the ground characterization and ground failure data in Christchurch are unparalleled. Thus, they provide a unique opportunity for advancing knowledge and practice in liquefaction engineering. Sampling and advanced cyclic testing of the troublesome silty sands in Christchurch is performed to characterize their cyclic resistance. This work enables comprehensive documentation of insightful case histories of building performance at sites undergoing different levels of liquefaction-induced ground failure. Fully nonlinear effective stress back-analyses of the case histories evaluate the importance of soil-structure interaction effects for buildings at liquefaction sites. Additionally, a liquefaction outreach website will bring liquefaction into the classrooms. Learning from design level earthquakes is invaluable to advancing the earthquake profession. Liquefaction effects research is vitally important in the U.S. where the occurrence of the massive liquefaction that occurred in Christchurch could literally destroy a city. The similarity of the Christchurch liquefaction hazards and infrastructure with those in the U.S. means that the research findings will be directly transferable to U.S. cities of comparable size, as well as scalable to larger urban centers. The 2010-2011 Canterbury earthquake sequence provides the opportunity for an integrated study of blocks of buildings at a degree of detail and level of complexity that could not be performed in the U.S. due to security restrictions. Importantly, the research focuses on the effects of liquefaction on structures as opposed to the phenomenon itself, thus advancing the state-of-the-practice in liquefaction engineering. The project supports continued international collaborations between New Zealand and U.S. earthquake researchers and allows a U.S. Ph.D. student to establish research contacts in New Zealand.