EAPSI: Achieving seismic resilience by understanding liquefaction effects in Christchurch, New Zealand

Beyzaei Christine Z, Fremont CA

Investigators

Abstract

Earthquakes are natural hazards that occur throughout the world, causing ground shaking and the potential for significant damage. During ground shaking, water pressure in the surrounding soil increases. When the water pressure exceeds a certain threshold, the soil collapses, becoming fluid and flowing up through the ground surface. This phenomenon, called liquefaction, causes ground settlements that affect both above- and below-ground structures. During the 2010-2011 Canterbury Earthquake Sequence, several large earthquakes took place over a 16 month period near Christchurch in New Zealand. Liquefaction damage from these earthquakes affected a significant large area around Christchurch, damaging buildings, infrastructure networks, and critical lifeline systems. This degree of extensive repeated liquefaction was virtually unprecedented in a modern urban setting. Through field sampling in Christchurch and a geotechnical laboratory testing program, this research will contribute to the current understanding of liquefaction. This research will be conducted at the University of Canterbury, in collaboration with Dr. Misko Cubrinovski. During the post-earthquake engineering investigation in Christchurch, an important observation was made: state-of-practice methods incorrectly predicted the occurrence and severity of liquefaction for many sites with fine-grained (silty) soils. State-of-practice methods for assessing liquefaction potential are largely based on clean sands; there remains considerable debate as to whether fine-grained soils will liquefy and the appropriate assessment procedure to employ. This research aims to advance the state of knowledge on liquefaction of fine-grained soils, while evaluating the level of conservatism in current state-of-practice liquefaction assessment methods. Hydraulic fixed-piston soil samples will be obtained from sites throughout Christchurch and cyclic stress ratio (CSR) curves will be developed through cyclic triaxial testing. Laboratory results will be compared with post-earthquake field observations and established liquefaction assessment procedures to evaluate the nature of liquefaction in fine-grained soils. The implications of these results will advance seismic resilience for cities faced with similar liquefaction hazards. This NSF EAPSI award is funded in collaboration with the Royal Society of New Zealand.