Research

Performance of a Shallow-Founded Building on Liquefiable Soil at the Port of Wellington during the 2013 and 2016 New Zealand Earthquakes

The 2016 Mw 7.8 Kaikōura earthquake caused widespread liquefaction-induced damage at the Port of Wellington (CentrePort), New Zealand. Conversely, less intense, shorter duration ground shaking during the 2013 Mw 6.6 Cook Strait and Lake Grassmere earthquakes caused only moderate to no damage. The PM4Sand, PM4Silt, and UBCHyst constitutive models implemented in FLAC are used to evaluate the seismic performance of a shallow-founded structure at CentrePort. Nonlinear effective stress site response analyses are performed first to calculate the ground shaking at a strong motion site at the port using deconvolved motions from a nearby site. The analytical results agree with the recorded ground motions. The input ground motions are employed in two-dimensional nonlinear dynamic analyses of the 2-story reinforced concrete frame structure on spread footings for the three earthquakes. The building and surrounding ground settled 230-260 mm following the 2016 Kaikōura earthquake yet suffered no-to-minor damage during the 2013 earthquakes. The analyses reliably captured the observed performance during the earthquakes. Negligible settlement was estimated for the 2013 earthquakes, and the volumetric-induced liquefaction mechanism governed the seismic performance of the structure in the 2016 Kaikōura earthquake with only minor shear-induced settlement. Shear-induced settlement was minimal due to the light structural loads of the building and thick compacted gravel crust. Recently developed design procedures to estimate liquefaction-induced settlement are evaluated and are shown to provide reasonable results.

Collaborators: Jonathan D. Bray, Ph.D., P.E., NAE