Sea Change: Safeguarding Tāmaki Makaurau
Each day, thousands drive, walk, cycle or alight from buses, trains and ferries on Auckland’s downtown waterfront. Although the area is the city’s heart, few know how vitally its existence depends on a 600-metre seawall running underneath it.
“Without the seawall, large parts of downtown Auckland would be underwater,” says Eric van Essen, Auckland Transport (AT) Downtown Programme Director.
The recently completed $73 million seawall-strengthening project, proudly delivered by Tonkin + Taylor in partnership with AT and Downtown Joint Venture contractors, aims to make sure that the seawall stays intact for many years to come.
Built to support the young city’s land reclamations in the late 1880s and early 1900s, the old seawall needed to meet today’s building standards for safety and earthquake resistance. Its original construction had not considered earthquakes, meaning there was a serious seismic risk to Quay Street. Addressing this may have seemed simple in principle, but in practice the undertaking was highly complex.
As one of six Downtown Infrastructure Development Programme projects commissioned to build a more resilient waterfront for Auckland, the seawall-strengthening project was foundational, with the full programme of works relying on the project commencing quickly.
This demanded that our team deliver the designs and consents in an extremely short timeframe, a challenge that they met with excellence.
Once work began, new challenges arose. Many underground utility services for power, internet, water and sewage ran under Quay Street adjacent to the seawall, meaning we had to find ways to strengthen Quay Street while avoiding significant relocations of these services.
Crucially, completing complex consents was a massive challenge. Says van Essen: “Getting the consents on time was the make or break of our meeting the programme timeframes that we had committed to. The team showed remarkable skill in working with stakeholders to reach agreement and find solutions.”
Construction was also highly challenging, as it required the use of specialised large machinery on variable ground over reclaimed land. Work would also need to be undertaken in a constrained space.
Despite the added complication of COVID-19 restrictions, consenting and design work that began in 2017 was successfully completed in January 2020. Even better, the whole project came in under budget and ahead of deadline, which is rare for such a large and complex project.
Mark Foster, Tonkin + Taylor Design Manager, who managed the design and delivery of the seawall project in conjunction with the five other Downtown Infrastructure Development Programme projects, says, “The project’s success came down to our expertise, the quality of relationships and the sheer strength of the consulting team’s work.”
Dr Luke Storie, Tonkin + Taylor Geotechnical Engineer, led the seismic-strengthening design alongside Foster. Working collaboratively with a team of planners, led by Tonkin + Taylor Technical Director – Planning, Jennifer Carvill, seismic strengthening options were developed that meant we could meet the needs of stakeholders while simultaneously navigating challenging project requirements.
“Right from the outset we knew we needed a consenting strategy that responded to tight timeframes and an evolving design process,” says Carvill. “By consenting the project in four discrete sections, we were able to deliver resource consents that were fit for purpose right when the construction team needed them. The design and construction methodology used for each section was specific to the ground conditions, the existing seawall’s condition and the needs of key stakeholders in each location.”
The Ferry Basin, and the area adjacent to the Ferry Building, used inclined rock anchors to strengthen the existing seawall while a palisade wall approach, involving 96 reinforced-concrete piles, was used to strengthen the 300 metres between Queens Wharf and Marsden Wharf.
Significant cost and time savings were realised in the Queens Wharf to Marsden Wharf section through key design innovations. Targeted geotechnical investigations and testing, after the concept design phase, allowed the removal of anchors, saving significant cost. Extensive proof drilling at every pile greatly eased the process of removing a capping beam proposed for the palisade wall, which was going to cause significant delays in construction and affect the delivery of the Quay Street Enhancement project above the piles.
“We worked closely with AT and the construction team in the early design phase to enable the removal of the anchors and capping beam in the Queens Wharf to Marsden Wharf section, says Dr Storie. “The proof drilling also meant construction was efficient, showing the depth each pile was going to be and meaning that the length of the reinforcing cage did not have to be adjusted on site.”
The construction team and the Downtown Joint Venture contractors also worked with an emerging technique called jet grouting. This involved drilling 200-millimetre-diameter holes down to a hard layer such as rock, then injecting and mixing a water/cement mixture into the soil using a rotating nozzle, forming a column as it moved from the hard layer up to just below ground level.
The jet grout columns enabled construction to occur efficiently around many utility services and required a smaller construction area to keep Quay Street flowing. An innovative design was required as jet grout columns are not typically used to this extent for seismic strengthening. The flexible consenting strategy meant we were able to respond to this design change after applications for resource consent had been lodged and still deliver consents on time.
Effective collaboration with AT’s stakeholder engagement and development response teams meant stakeholder issues were dealt with quickly and successfully. The team worked with the Auckland Council consents team to develop conditions that were consistently applied to different components of the project, ensuring quick turnarounds of consent decisions and minimising appeals.
The project was a vital first piece of a jigsaw in completing a wide range of work downtown, enhancing Quay Street with wider footpaths, easier navigation, vegetation and new street furniture. The city’s vital seawall now has modern seismic protection for the next 100 years, and generations of Aucklanders and visitors will get even more enjoyment from their waterfront.