The impact of a PEER funded research project “Liquefaction Triggering and Effects at Silty Soil Sites” is highlighted below. The project Principal Investigator is Jonathan D. Bray, Faculty Chair in Earthquake Engineering Excellence, Professor of Civil Engineering, UC Berkeley. The research team includes Daniel Hutabarat, Graduate Student Researcher, UC Berkeley.
Learning from observations after design-level earthquakes is invaluable to advancing understanding in earthquake engineering. Investigating the occurrence or nonoccurrence of liquefaction of stratified deposits of silty and sandy soils and evaluating the effects of liquefaction on bridges and lifelines provide invaluable information that will serve as benchmarks to our understanding of soil liquefaction. The geologic data can be used to improve current empirical liquefaction triggering procedures and their consequential effects. Most of the liquefaction data currently available relates to sandy soils, so careful examination of silty soil sites will assist greatly in broadening the applicability of design methods.
The over-prediction of liquefaction triggering by current procedures at silty soil sites in Christchurch appears to be due to their inability to capture the seismic performance of stratified silty soil deposits. The empirical database used to develop these procedures consists primarily of liquefaction triggering data from sand sites. Conservatism of the empirical liquefaction triggering procedures also contributes to the over-prediction of liquefaction. Engineers are currently faced with a dilemma: How can the prediction of liquefaction in these silty soils using established liquefaction triggering procedures be reconciled with the contradictory observations that surface manifestations of liquefaction were not observed after intense shaking from the Canterbury, New Zealand, earthquakes? This project will develop insights that will enable engineers to adjust state-of-the-art liquefaction procedures to address the discrepancy of their over-prediction of liquefaction triggering with the field observations that stratified silty sites of particular characteristics do not manifest liquefaction and damage bridge foundations.