Richard Silcock rekindles naval history and the challenges encountered by the design and construction teams in turning an unstable Auckland cliff into a commendable memorial and lookout.
Development of Achilles Memorial in Auckland’s St Heliers Bay required geotechnical expertise, significant piling, a large palisade wall, a timber boardwalk, a cantilevered viewing platform, a stone wall, flagpole, hand-railing and landscaping – all in just under nine weeks!
Next year marks the 80th anniversary of a significant WW2 naval battle – the Battle of the River Plate (1) in which three allied cruisers took on the might of the heavily armed German battleship, the Admiral Graf Spee off the coast of South America.
Although no match for the German ship, and despite the allied ships sustaining considerable damage they chased the battleship into the neutral port at Montevideo in Uruguay. Thought to be faced with an armada of allied ships and damaged herself, the Graf Spee was several days later sailed out of the harbour and scuttled in the River Plate estuary– a victory and moral boost for the allies.
During the battle, the Leander-class light cruiser of the NZ Navy (2), HMNZS Achilles, was directly hit by enemy fire, resulting in the loss of four lives and a number wounded, including the Captain.
In 1940, to mark this country’s prominence in the battle, a headland east of St Heliers Bay in Auckland was named Achilles Point as it resembled the bow of a ship. A reserve was established and a small memorial erected.
In 2008, a 285-metre palisade wall (one of the longest in the country) was constructed at a cost of $5 million by Brian Perry Civil (BPC) to arrest subsidence of reserve land on the cliff side, adjacent to and towards the western end of the road leading to the site.
To mark the 70th anniversary of the historic event, the Auckland City Council embarked on a project to construct a more fitting memorial and lookout on the site.
A concept design by architects, the Isthmus Group, for a boardwalk, viewing platform and landscaping was accepted by the council and Tonkin and Taylor (T and T) were appointed structural design and geotechnical consultants. BPC was appointed construction engineers (3).
In addition, the Isthmus Group was appointed to provide environmental and landscaping design, Greenscene – arborist services, Transfield – electrical design, and Holmes Consulting – construction peer review, along with numerous other subcontractors.
The eroding cliff face at the headland and the confined shape of the site provided the design and construction teams with a unique set of challenges.
The design and construction also had to be fast-tracked, as there was just under nine weeks before the actual anniversary on December 12, 2009. BPC, awarded the contract on Friday October 9, began work the following Monday with the design team working in tandem.
Due to the nature of the cliff face and general instability, considerable geotechnical work was carried out to establish soil and rock composition (largely weak sandstone and mudstone) and to ‘map’ the roots of protected pohutukawa trees which are a feature of the site (4).
“The concept design for the memorial lookout called for robust structural input, especially in relation to the viewing platform and in addressing the erosion of the cliff,” says Geoff Radley, a senior structural design engineer with T and T.
“Utilising a tied-back, 110-metre palisade wall along the north-eastern section of the site and a continuous concrete capping beam structure was seen as the only appropriate solution for retaining the site and providing certainty of the structure over a 100-year design life expectancy.
“By tying the cantilevered viewing platform to the palisade wall and supporting it on two drilled piles near the edge of the cliff provided for future cliff regression.
“It was also the least obstructive solution with the piling and substructure hidden beneath the boardwalk and viewing platform deck,” he says.
Within several days of construction work commencing, a temporary pile-drilling platform was built and concrete piles were driven to a depth of between 15 and 22 metres.
“The piles were 600–750mm in diameter with 1.5 metre centres and were connected with the concrete capping beam, which was anchored into rock using inclined multi-strand anchors,” says Matt Findlay, who was BPC’s operations manager during the construction.
“Due to the narrowness of the reserve, the ground anchors were inclined 45-50 degrees to the horizontal to avoid drilling under private property.
“A tied bulkhead design was used where the two palisade walls on the western and north-eastern sides were tied together using high tensile steel rods to provide further lateral stability.”
To overcome the problem with the trees and avoid damaging them, Greenscene was able to dig drenches to expose the tree roots using the ‘mapped’ plans to locate them.
Matt says that to avoid the roots a number of the pile positions had to be revised and changes made to pile diameters.
“We also had to alter the spacing and capping beam level to avoid them. This in turn required some amendments to the boardwalk design,” he says.
The design and construction of the cantilevered and sloping viewing platform, some 32-metres above sea level and jutting out seven-metres from the cliff was driven by the limited number of foundation options applicable to the site.
Following exploratory boreholes being drilled to ascertain stability, two pile foundations were seen as the most appropriate solution as it allowed for the viewing platform to be cantilevered out past the outer-most pile.
Then after the construction of a 12-tonne, reinforced steel frame it was craned into position and aligned with the reinforced concrete pile caps to form the substructure for the platform.
“This connection of the capping beams and the frame was complex due to the geometry of the platform slope,” says Matt.
“It required careful manoeuvring before it could be bolted into position. A bolted, spliced connection was also incorporated to allow for the future removal of the outer section should the cliff erode in the future.
“Logistics and careful planning played an important part in getting the project completed on time,” he says.
“For instance, the fabricated steel framework for the viewing platform was assembled offsite, as this allowed the concrete and timberwork to progress unhindered.”
A commemorative plaque set in a basalt stone wall, a naval flag pole, wave-shaped handrails, seating and attractive landscaping completed the project. In addition and in recognition of the site being once a Maori pa site, three totara po were specially carved and erected on the boardwalk.
“Health and safety was also given prominence in all aspects of the construction,” says Ron Caesar, who was BCP’s site manager for the project.
“Due to the number of people on site we instituted weekly meetings to ensure all work was appropriately planned and safety measures initiated.”
It was only due to the fast-tracking of the design, excellent planning, obtaining rapid resource approvals and break-neck construction that the project was completed on time.
Such was the tightness of the time-frame, some finishing details were still being completed a few hours prior to the dawn blessing, official opening and dedication ceremony.
“All those engaged in the project were effective in developing practical solutions to often complex problems as the project progressed,” says Matt.
“As could be expected, challenges arose from the site conditions.
“There was also a high level of workmanship displayed by our suppliers despite the tight time-frames. For example, George Grant Engineering who provided the fabricated steel structure and KB Construction who did the timberwork for the decking both did an excellent job.”
In the spirit of Christmas, Auckland’s mayor at the time, Hon John Banks, delivered platters of food to the construction team in recognition of their hard work and the dedication they had shown – often working long hours in unfavourable weather to get the project completed on time.
The complexity of the project was recognised at the annual INGENIUM Awards, with the memorial gaining an award for council projects under $2 million. It also won an ACENZ merit award and was nominated for a CCNZ Award.
The completed memorial commands an unequalled view of the Waitemata Harbour, Rangitoto and the Hauraki Gulf and has proven popular as a vantage point with Aucklanders and visitors alike – a reflection on the success of the project and what it stands for.
“Like the naval battle, where there was dedication and a willingness to tackle insurmountable odds, all parties involved in the project showed a willingness to bring the project to completion, on time, to budget ($1.75 million) and to an extremely high standard,” says Markus Pillay, Auckland Council’s principal project engineer at the time.
“To quote the motto of the ship’s company: “Fortiter in Re – Firmness in doing what is to be done; an unflinching resolution to persevere to the end.”
(Footnotes)
- The Battle of the River Plate (Rio de la Plata) took place between December 12 and 17 1939 in the South Atlantic, near the expansive river delta separating Uruguay and Argentina.
- HMNZS Achilles was on loan from the Royal Navy. Up until 1941 the NZ Navy operated as a division of the RN with senior officers seconded from it, however most of the crew were New Zealanders.
- Brian Perry Civil (a construction division of Fletcher Construction) was appointed following a tendering process and because they had had previously been involved with the site to stabilise erosion in 2008.
- The dual level of the boardwalk was specially designed to avoid removal of the pohutukawa roots.