There is a pressing need to investigate the seismic response of silty soils at sites that were strongly shaken during the 2010-11 Canterbury, New Zealand (NZ) earthquakes but did not exhibit evidence of liquefaction, although state-of-the-art liquefaction procedures indicate that significant ground failure should have occurred. The overestimation of liquefaction-induced ground failure by current procedures could potentially waste millions of dollars during the Christchurch recovery in addition to costs incurred worldwide, because engineers are requiring expensive ground improvement or building foundations where these procedures indicate that liquefaction is likely. The NZ government is keen to fund research on this important topic and desire international participation. A comprehensive NZ proposal has been developed to perform additional testing to advance their understanding of the role of fines in liquefaction triggering and ground failure. They are eager to partner with US researchers in this effort. The over-prediction of liquefaction triggering by established procedures appears to be a result of their inability to capture the response of silty soils. The empirical database used to develop these procedures consists primarily of triggering data from clean sand sites. Conservatism of the empirical liquefaction triggering procedures also contributes to the over-prediction of liquefaction. To evaluate conclusively the liquefaction potential of low plasticity silty soils requires advanced laboratory testing. As the Christchurch recovery continues, engineers are faced with a dilemma - How can the prediction of significant liquefaction in these silty soils using established liquefaction triggering procedures be reconciled with the contradictory observation that little or no liquefaction damage was observed during strong shaking on multiple occasions? The question is of great importance for developing practical engineering solutions that strike a sensible balance between risk and affordability.
This research takes advantage of the substantial work already performed in NZ to guide the rebuilding of Christchurch. The NZ government funding agencies are only interested in this effort if it can be performed quickly so it can assist engineers and planners during their rebuild. Thus, the work is urgent, and U.S. researchers must participate during the compressed NZ work schedule. This work leverages prior and current research in Christchurch funded by the NSF and does not duplicate ongoing efforts. The high-quality case studies and associated laboratory testing and analysis developed through this research will advance ongoing research regarding the liquefaction of silty soils and enable widespread benefits worldwide. Documenting and learning from observations after design level earthquakes are invaluable to advancing our understanding in earthquake engineering. Investigating the occurrence or nonoccurrence of liquefaction of silty soils and evaluating the effects of liquefaction on buildings and lifelines provide invaluable information that will serve as benchmarks to our understanding of soil liquefaction. This project will provide high-quality data from post-earthquake observations, geotechnical investigations, and laboratory testing to the worldwide research community. These data can be incorporated into the existing international dataset to help improve empirical correlations regarding soil parameters, liquefaction triggering, and consequential effects. Most of the research data currently available relates to sandy soils, so addition of this information regarding silty soils will assist greatly in broadening the applicability of empirical design methods. Lastly, the proposed research supports an international research partnership that will advance knowledge worldwide in liquefaction engineering while providing critical information to NZ engineers during their urgent rebuild.
