Liquefaction assessment of reclaimed land at CentrePort

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2020
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Dhakal, Riwaj
Cubrinovski, Misko
Bray, Jonathan
Abstract

The 2016 Mw7.8 Kaikōura earthquake caused widespread liquefaction in the port of Wellington (CentrePort) which produced substantial ground movements, damage to structures and thick surficial manifestation of ejected soil. Observations of liquefaction-induced damage provide an opportunity to evaluate the applicability of widely used state-of-the-practice simplified liquefaction evaluation methodologies on the end-dumped gravelly fills and hydraulically-placed silty and sandy fills at CentrePort. Liquefaction assessment of the gravel reclamation poses several challenges due to its large percentage of gravel-sized particles making it difficult to obtain high-quality in situ data. The hydraulic fills at CentrePort are also of significant interest as they relate to a range of issues in the simplified engineering assessment around effects of fines and their plasticity on the liquefaction resistance. Detailed damage inspections after the Kaikōura earthquake involved accurate measurements of ground deformations, well documented damage to structures, and good mapping of surficial evidence of liquefaction. Subsequent subsurface exploration investigated the thick end-dumped gravelly fills and hydraulically-placed dredged reclamations. Fieldwork included 121 CPTs, several shear wave velocity profiles, and logging of boreholes with soil samples collected from around the port. These investigations were utilised to develop detailed subsurface soil profiles for the reclamations. The spatial distribution, thicknesses, and depths of the fills were investigated and characteristic layers were identified. Grain-size curves and Atterberg test results gave insight into the properties of the fill material. Results of CPT-based liquefaction triggering and post-liquefaction reconsolidation settlement assessments using state-of-the-practice procedures were compared with observed damage and measured ground deformations. The next stage in this study is monotonic and cyclic loading of fill samples to determine the liquefaction resistance for characteristic densities/states of the fill deposits.

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