Abstract
Wellington’s waterfront is in demand for new developments due to its proximity to the central business district, infrastructure, and harbour. This area can be impacted on by several hazards like earthquake shaking, liquefaction and lateral spread, see level rise and tsunami (tsunami not considered in this paper). The waterfront was reclaimed in a number of stages beginning in the 1850s, mainly by end tipping of weathered gravels. Liquefaction and lateral spread of these gravels as a consequence of a strong earthquake shaking event is likely to occur as was observed in the recent M7.8 Kaikōura earthquake in November 2016. This paper presents a case study of a five-storey building currently being constructed on the Wellington waterfront. To mitigate the impact from some of the natural hazards and to provide a resilient structure various foundation and ground improvement systems were considered. An in-ground cellular foundation solution was selected. This solution offers: liquefaction mitigation, shear resistance to resist lateral spread beneath the building, foundations for the new structure, temporary basement walls and effective cut-off of ground-water flow during construction. The foundation selection process, features and associated risks are discussed in this paper.
1 INTRODUCTION
Since the 2011 Canterbury earthquakes and 2016 Kaikōura earthquake, ‘resilience’ is one of the main focuses while designing foundations and substructures on sites prone to liquefaction and lateral spread such as the Wellington waterfront.
A five storey building with a basement is currently being constructed on the Wellington waterfront. While the waterfront provides unique location and amenity advantages for developments, the ground conditions are very challenging and complex.
The building design includes base isolation to prevent the building’s superstructure from absorbing earthquake energy, with ground improvement to support the base isolation system and provide a high level of resilience to earthquake damage.
This paper discusses the foundation options considered for this complex site, the basis of selecting the in-ground cellular foundation solution and its features and associated risks and hazards.
2 PROJECT INFORMATION
2.1 Proposed development
A five storey building with a basement beneath approximately 90% of the building footprint is currently being constructed on the Wellington waterfront (refer Figure 1 for site location). The building owner wanted to provide a high level of resilience under an extreme earthquake event, including a lower potential for damage in a severe event than a normal office building.
The building design includes base isolation to provide high seismic performance by reducing the extent to which the building’s superstructure absorbs earthquake energy. To support the base isolation system and ensure this high seismic performance, ground improvement was needed to reduce liquefaction and lateral spread.
