Get ready to breathe a sigh of relief: one of Auckland's most disruptive, complained-about civil works projects is three-quarters finished.
The $75 million, 600m-long Quay St seawall strengthening is around 70 per cent complete after two major sections from Queens Wharf to Marsden Wharf and Princes Wharf to the Ferry Basin were finished.
Eric van Essen, Auckland Transport's downtown programme director, said work was now well under way in the Ferry Basin and that marked about three-quarters of the project finished.
Asked about completion dates, he said "January or February" next year.
The project narrowed the busy east-west waterfront thoroughfare to chokepoint, as businesses and politicians complained about lengthy delays since it started last year.
• Milford beachfront residents thought rocks OK to strengthen seawall
• Opinion: Clifton Seawall needs finishing touch
• Premium - Ruakākā resident upset about council's seawall plan
• $800,000 Castlepoint seawall complete, side issues still being considered
In April, the Herald reported on a doubling of commute times along Quay St had politicians and the AA criticising a lack of planning around the major roadworks "madness".
The arterial four-lane Quay St, running the length of Auckland's CBD and parallel to Waitematā Harbour, has been reduced to a single lane each way since December.
The Auckland Transport Downtown Programme responsible for the roadworks is a total revamp of the city waterfront area, costing $321m and incorporating six major projects for the 2021 America's Cup.
On the traffic, van Essen said: "We appreciate Aucklanders' patience. We've had extensive traffic management and it's been very disruptive but we have been able to keep both lanes open. This is only a once-in-100-years job."
Seawall work was going according to schedule, he said. The recent completion of jet grout piling in the Princes Wharf to Ferry Basin section was a major benchmark in the programme.
The strengthening, in four sections, starting mid last year and due to finish early next year, is:
• Princes Wharf to Ferry Basin: jet grout column construction complete, all 153 jet grout columns in place.
• Queens Wharf to Marsden Wharf: palisade piling construction complete, all 104 palisade piles now in place.
• Ferry Basin: incline anchor construction started mid-2019 and will finish late this year, 14 of 29 inclined anchors now complete.
• Ferry Building: incline anchor construction due to begin later this year and finish early next year when 21 sub-vertical incline anchors will be installed west of the Ferry Building through the existing seawall.
Van Essen said the area was expanding, with the $1b Commercial Bay and the $1b-plus Britomart redevelopment and restoration.
The old wall was between 100 and 140 years old in some sections and protected Quay St and the services that run beneath it, future-proofing the CBD for the next 100 years.
Without the seawall, large parts of downtown Auckland would be under water, he said.
The strengthening process was designed to add resilience to a one-in-2500-year event or a 6.5 magnitude earthquake. It also allowed for a sea-level rise up to 1m during 100 years and was in line with climate change guidelines and predictions, he said.
Since an initial assessment in 2012, urgent work was finished. Divers have carried out annual monitoring to ensure nothing more urgent needed attention till the work started, van Essen said.
"For a project of such large scale, significant planning, logistics and designs must be undertaken to ensure we do it once and do it right," he said.
He emphasised the existing mainly bluestone rock wall was remaining in place "to protect from the sea but a second wall has been built behind that. We left the old seawall in place because it's heritage as well. The new wall has been built behind for resilience for the next century".
Three techniques are being used in four seawall sections due to location, the suitability of ground conditions, design requirements and level of disruption, he said. Those four are:
• palisade wall, complete: 104 piles 1.2m in diameter from 12m to 30m have been inserted into pre-drilled holes and socketed into the bedrock to form an in-ground wall. The piles are spaced 2.4m-3.6m apart.
• jet grouting, complete: 153 jet grout columns have been successfully installed between Princes Wharf and the Ferry Basin. Grout is pumped into pre-drilled holes to form columns from bottom to top. The columns of 1.4m-1.7m in diameter are laid in an interlocking fashion to provide strength and stability. Jet grouting is used where there is a high concentration of utility services and the palisade wall option would compromise those services.
• anchoring existing seawall, under construction: a series of incline anchors are drilled through the seawall into the bedrock spaced around 3m apart. The seawall is also bolstered by installation of a series of reinforcing bars spaced 0.7 m apart along the length of the anchored section. The anchoring approach causes less disruption to the operation of the Ferry Basin and allows a co-ordinated approach with other downtown programme projects.
The seawall forms the harbour edge of an historic land reclamation that supports Quay St and the services under the road corridor.
The first sections of this reclamation were built between 1875 to 1886 along what is now Quay St west of Britomart, and also east of Britomart parallel to Beach Rd. Subsequent sections were added after the turn of the 20th century.