Assessment of the Performance of the Ground and Facilities at Wellington Port during Three Earthquakes

University Of California-Berkeley, Berkeley CA

Investigators

Abstract

Ports are critical economic assets and their resilience is necessary for the security of our Nation. Many ports are in seismically active areas, which could be damaged and lose operational readiness after an earthquake. Research on liquefaction effects on ports is vitally important in the U.S. where the effects of liquefaction like those observed at Wellington Port, New Zealand after the 2016 Kaikoura earthquake could kill people and cripple commerce. As widely used liquefaction evaluation procedures are largely empirically based, it is crucial that well-documented, insightful liquefaction case histories be investigated thoroughly. There remain several important issues to explore such as gravel and silt liquefaction and their effects on port facilities. The rich Wellington Port dataset provides an exceptional opportunity to advance the understanding of soil liquefaction effects, to develop more robust simplified procedures, and to evaluate the capabilities of advanced models and simulations to discern the seismic performance of critical port facilities. Wellington Port provides the opportunity for an integrated study of port facilities at a degree of detail and level of complexity that could not be performed in the U.S. due to security restrictions. The similarity of its liquefaction hazards and infrastructure with those in the U.S. means that the research findings will be directly transferable to the U.S. Lessons learned will be incorporated in recommendations for assessing the effects of liquefaction on port facilities built on reclaimed land. Simplified liquefaction evaluation procedures provide useful insights, but they cannot explain the different levels of liquefaction-induced ground and facility damage during the 2016 Kaikoura earthquake at Wellington Port. The effects of this event and the less damaging 2013 Cook Strait and Lake Grassmere earthquakes warrant further study. Performance-based earthquake engineering requires analytical tools that can discern varying levels of seismic performance. These earthquakes, with their excellent ground motion recordings, their well-documented performance of port facilities, and subsequent fieldwork to characterize the soil conditions, which includes gravel that liquefied, provide an exceptional opportunity to advance understanding. Documenting and learning from field case histories of gravel liquefaction are especially important, as few of these cases exist. The research goals are to: a) investigate liquefaction triggering of the Thorndon fill with up to 70% gravel-size material; b) investigate the lack of liquefaction manifestation at silty soil sites at the port; c) develop a new probabilistic method for estimating post-liquefaction volumetric settlement; d) develop and back-analyze case histories of port facilities undergoing different levels of liquefaction-induced ground failure; and e) transfer knowledge. These goals are realized through a research plan that: (1) develops and interprets well-documented case histories of ground performance for three soil conditions at the port: gravel fill, silty soil, and sand fill; (2) combines the Port’s lidar data with other case history data to develop a new probabilistic method for estimating volumetric reconsolidation ground settlement, which assesses uncertainty; (3) develops and back-analyzes seven well-documented case histories of port facility performance to evaluate the importance of soil-structure-interaction effects for wharves and buildings; and (4) performs outreach activities and develops guidance. The excellent case histories of ground and structural performance at Wellington Port provide an exceptional opportunity to develop new methods that capture the observed differing levels of performance during the earthquakes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.