EAPSI: Reconciling Overprediction of Liquefaction-Induced Damage in Christchurch, New Zealand by Considering Spatial Variability

Munter Sean K, Davis CA

Investigators

Abstract

Widespread soil liquefaction during the events of the 2010-11 Canterbury Earthquake Sequence caused severe damage to the infrastructure and economy of Christchurch, New Zealand. Liquefaction occurs during earthquake shaking in sandy and silty soils, prevalent in the Christchurch region, and is characterized by strength loss resulting in ground deformations that can damage buildings, roads, pipelines, etc. In certain areas of Christchurch, conventional methods for assessing liquefaction damage potential tended to overpredict damages expected from these earthquakes; a common characteristic of these areas is the presence of thin liquefiable soil layers that are interlayered with non-liquefiable soils. Through collaboration with Dr. Misko Cubrinovski of the University of Canterbury in Christchurch, this project will utilize available field and laboratory data to perform numerical modeling of several sites with such interlayered soil deposits. Dr. Cubrinovski is an expert in geotechnical earthquake engineering and has been involved extensively in post-earthquake reconnaissance and research in Christchurch. The results of this work and the knowledge gained will provide a foundation for improved methods and guidance for evaluating liquefaction damage potential. Previous work by the researcher has shown that in deposits of finely interbedded liquefiable and non-liquefiable soils, ground deformations can be limited by the non-liquefiable soil when pockets of liquefiable soil are laterally discontinuous. This is not considered in conventional methods, which are one-dimensional. The modeling to be performed will involve using a geostatistical approach along with available site data to build stochastic two-dimensional subsurface models of the sites and then performing dynamic analyses using ground motion records from the earthquakes. The intent is to see if inclusion of spatial variability in stratigraphy explains why liquefaction did not lead to damaging ground deformations for the shaking levels produced by the earthquakes. The issue of overprediction of liquefaction-induced damages has great significance, as the conventional methods for assessing damages are widely used in engineering practice around the world. As such, this work not only contributes to the ongoing recovery of Christchurch but also has an impact on assessment of liquefaction hazards in general. This award under the East Asia and Pacific Summer Institutes program supports summer research by a U.S. graduate student and is jointly funded by NSF and the Royal Society of New Zealand.