With time and budget constraints plus significant site issues, a one-of-a kind “jump start” technique was used to deliver a stellar urban regeneration project.
Sydney is Australia’s economic epicentre, but most of its inhabitants don’t live anywhere near the city’s harbourside central business district.
With a burgeoning workforce of 23,000 employees, there was an ever-growing need to develop a new CBD in the heart of greater Sydney – Parramatta.
Built, in joint venture with Obayashi (BOJV), was selected by Walker Corporation and Parramatta Council to deliver the project, which includes four commercial towers (4, 3 and 6&8 Parramatta Square), civic hub and public domain for the new $3.5 billion Parramatta Square precinct.
Among Australia’s largest ever urban transformations, the new precinct has ensured Parramatta is recognised as one of the most connected cities in the world, accommodating several top-tier private sector and government institutions including Property and Development NSW, the Australian Taxation Office, Australian Broadcasting Corporation, Link Market Services, Westpac, Deloitte, Endeavour Energy, NAB, and LG, said Patrick Polomka, Senior Project Manager, Walker Corporation.
“Combining state-of-the-art workspaces with the highest achievable sustainability credentials and premium amenities, it will improve social and economic outcomes for generations to come,” he said.
However, there were several hurdles to navigate in the design and construction of the precinct, including site and regulatory issues. Here’s how BOJV and Walker managed to overcome them – and receive a finalist nod in the 2023 Australian Construction Achievement Awards along the way.
Several challenges were unearthed throughout the design and construction of 4 Parramatta Square, beginning with a complex regulatory process that needed approvals from all levels of state and local government, said Polomka.
“The site’s proximity to the existing floodplain and adjoining sites with multiple levels required extensive consultation between project teams to deliver a highly resilient and connected precinct, with direct links to the public domain and all major transport hubs,” he said.
“The central location of 4 Parramatta Square made site access extremely challenging, as it’s surrounded by Parramatta Railway to the south, the Sydney Water building and University of Western Sydney to the east and several existing developments along Macquarie Street.”
Challenging geotechnical ground conditions due to the existence of a large igneous dyke running diagonally through the precinct also posed problems, said Peter Whyte, Construction Director, Built.
“This resulted in the requirement for a diaphragm retention wall and a permanently anchored hydrostatic basement structure to deal with the high ground water pressures,” he said. “These conditions would typically add a significant period of time to a construction program.”
Creating a “jumpstart” solution
To mitigate these challenges, and others, a “jump start methodology” utilising structural steel was employed.
“The site had no direct access, being bounded by a large commercial building to the east, the existing Parramatta train station and rail corridor to the south, as well as the large excavation zones for the balance of the precinct to the north and west,” said Polomka. “The team had to create through access to the site, which meant we had to rapidly build to street level.”
These conditions, coupled with a construction program that couldn’t be met with a conventional build, meant BOJV had to implement innovative methods, said Whyte.
“4 Parramatta Square was run as a competitive tender. Due to early handover requirements, BOJV had to realise opportunities through clever construction sequencing that reduced the overall construction duration and associated plant and labour costs to ensure we remained competitive so we could secure this coveted project,” he said.
“[We] took advantage of the building’s impressive elevated podium level design to reach the typical floors earlier, removing a total of six suspended levels plus the 1.5 metre thick hydrostatic slab off the critical path.”
Adopting a sequence of work that accelerates upper floors of a building through the use of 3 to 4 storey high concrete-filled steel tube columns, a jumpstart technique bypasses intermediate floors – allowing a structural steel floor plate to be constructed earlier than if built floor by floor from the basement up, said Richard Hodgett, Engineering Manager, Built.
“By repeating the jumpstart sequence, BOJV were able to install Ground Floor framing, Level 1, then Level 3 in quick succession, resulting in a triple jumpstart,” he said.
Once the team had progressed to Level 3, the tower’s typical floor structure could then progress using conventional post-tensioned and concrete floors to completion.
“The program remained on the critical path while the lower floors were ‘filled in’ underneath concurrently with the upper floors, saving a significant amount of time – approximately 12 weeks – compared to a conventional build,” said Hodgett.
Through extensive use of structural steel for both the vertical and horizontal structures, the jumpstart technique also facilitated the construction of elevated floors without extensive high-strutting form and falsework, markedly reducing the on-site labour required to erect the structure.
“The expansive podium design with inclined columns in steel could be constructed concurrently in a safer manner with the tower floor levels which were on the critical path,” he said.
Leveraging the technique
Following the success of the 4 Parramatta Square jumpstart methodology, BOJV used a similar technique at 6&8 Parramatta Square to again reduce the overall build program, said Hodgett.
“The installation of triple-height steel columns allowed the team to essentially jump the structure to the Lower Ground Floor, and then again up to Level 1 – enabling construction to start the typical cycles of the commercial floor slabs then drop back to infill the basement and podium slabs off the critical path,” he said.
To install these columns safely and efficiently, the team adopted 3D modelling to simulate the installation – using tower cranes to lift the steel while working around the jump-form core construction to ensure access was maintained at all times.
“The modelling allowed the team to identify clear pathways to install each column weighing up to 25 tonnes each,” said Hodgett.
Reaching new heights
At the time of construction, the jump start methodology used at Parramatta Square was one of the biggest in Australia, and the first of its kind with inclined columns, said Polomka.
“The jump start methodology helped 4 Parramatta Square achieve its two fundamental project goals of being delivered on time and under budget on a significantly constrained site,” he said.
“Using this methodology, we reached the typical floors earlier which allowed work to start on multiple levels, helping us achieve the tower’s extremely tight 24-month delivery timeframe for the base completion and interior fitout, which is a significant feat for a 40-level building.”