Building a resilient city – Quay Street Seawall
Running the length of Quay Street is a seawall. This historic seawall supports reclamation that was undertaken between 1879 and the early 20th century and has protected downtown Auckland for more than 100 years.
But it was never designed for earthquakes and is not going to last forever without some help.
During the last 18 months, Tonkin + Taylor (T+T) has been part of the team with Auckland Transport (AT) and the Downtown Joint Venture (DJV) contractors strengthening a 600-metre long section of the seawall.
Luke Storie, Geotechnical Engineer, has led the seismic strengthening design and our Design Manager Mark Foster has managed the design delivery of the seawall project as well as the other four projects within the Downtown Infrastructure Development Programme.
The designers worked collaboratively with the planners, led by our Technical Director – Planning Jennifer Carvill, to deliver separate resource consents for each section. This enabled us to work with AT to address the needs of a wide range of stakeholders on Quay Street, while we responded to challenging programme requirements.
“With the seawall being the first piece of the jigsaw puzzle required to complete the works Downtown, it was essential that the team delivered the design and consents really quickly,” says Mark. “The whole team pulled together to get a complicated job done in such a short time frame.”
Design and consenting the seismic strengthening of Quay Street was approached in four sections, using three methodologies. “The different methodologies were designed to work with the existing seawall location, key stakeholders, ground conditions, and design requirements,” Luke says. The final designs also help to minimise disruption.
The four sections of seawall include the area in front of Princes Wharf, the Ferry Basin, the area adjacent to the Ferry Building, and a stretch between Queens Wharf and Marsden Wharf.
The Ferry Basin and the area adjacent to the Ferry Building use inclined rock anchors to strengthen the existing seawall. In these two sections, high-strength steel tendons anchor the existing seawall to the rock and protect it from sideways movement during an earthquake.
The strengthening of Quay Street between Queens Wharf and Marsden Wharf uses a palisade wall approach, which involved constructing 96 reinforced concrete piles along the 300m length of the seawall. Each pile has a diameter of 1200mm and pile lengths vary from 10m to 25m.
Princes Wharf was a bit different.
“Princes Wharf has a lot of underground utility services in the area, such as internet, water, sewage, and power,” Luke says. “There were concerns early in the project about impacts to the tight construction programme if these underground utilities had to be relocated so the team had to find a way of strengthening Quay Street while avoiding significant relocation works.”
The team used a fairly new technique called jet grouting. This involves drilling 200mm diameter holes down to a hard layer such as rock and then injecting a water/cement mixture into the soil using a rotating nozzle, forming a column as it moves from the hard layer up to ground level. With the 153 jet grout columns now installed to help support Quay Street, the enhancement of Quay Street with wider footpaths, easier navigation, vegetation, and new street furniture can get underway.
A strengthened seawall is the foundation for the city, and Eric van Essen, AT Programme Director of the Downtown Programme, has said that the strengthened seawall is the foundation upon which all the other projects depend.
“While strengthening works have been highly visible requiring some very impressive construction and drilling equipment, the seawall itself is largely unseen beneath Quay Street,” says Mr van Essen.
“It is reassuring to know that this critical strengthening work will secure the resilience of the city against seismic events and climate change for another 100 years and beyond.”