The key objective of the “Early Works” is to provide a clear, clean site for the Main nSFM Construction Works. The “Early Works” involve the demolition of all wharf structures namely the “Hanson”, “Finger” and “Pre-Cast” wharves, including all sub-structure and piles, as well as redundant land-based structures and buildings including substations, office buildings, and a redundant coal loader. All wharf structures are to be demolished back to the existing seawall whilst ensuring, throughout the entire demolition process, that the latter is preserved and its current condition maintained for the Main Construction Works.
The Project site is located at the head of Blackwattle Bay, between the Pyrmont Peninsula and the foreshore of Glebe. It is situated less than 2km west of Sydney’s CBD. The site has a frontage to Bridge Road to the south and Blackwattle Bay to the north. There are several sensitive neighbouring stakeholders in close proximity to the works including a high school, residential dwellings, commercial buildings, recreational users of parklands and waters, and the existing Sydney Fish Market, a bustling touristic hub.
One of the 3 wharves, the “Hanson” wharf, is a 60-year-old structure comprising a concrete deck supported by timber beams and headstocks. Significant upgrade works to reinforce the deteriorated timber framework has been carried out over the two decades and the central part of the wharf underwent a complete rebuild 40 years ago to accommodate the construction of a concrete batching plant. The batch plant was demolished by Liberty Industrial earlier in 2020 as a precursor to this project. This central section of the wharf is composed of pre-cast concrete panels supported by concrete headstocks, pile caps, and piers.
The wharf is demolished working from the deck itself, systematically cutting the deck panels with concrete road saws, lifting the panels off to expose the supporting beams and headstocks, then removing these supports. The panels and supports are removed using 38t excavators fitted alternatively with hydraulic selector grabs or lifting chains with pipe-lifter mechanisms. The wharf piles are left in situ at this stage, they will be removed later on using a 35t crane barge. The central part of the Hanson wharf, being of a more recent and heavier design, requires progressive wire sawing and lifting of the supporting members.
The “Finger” wharf required a different approach due to a lack of technical information a marine-based approach is adopted – the wharf is to be demolished using a 35tcrane barge and a custom-built, specially designed system which allows to progressively deload the concrete deck, avoiding any need to cut the concrete blocks whilst holding onto them with the crane. This methodology was adopted as it presented significant risk mitigation factors and limited personnel exposure to the uncontrolled release of energy whilst separating the concrete blocks.
The “Pre-Cast” wharf is the most recent build of the 3 and is made of typical pre-cast, pre-tensioned concrete planks topped with a cast-in-situ concrete slab. These planks are supported by concrete headstock and piles. The wharf extends 25 meters from the seawall, therefore, can be demolished using a land-based approach involving a 250t crawler crane – the wharf deck is cut to full thickness in manageable sections using concrete road saws and lifted out progressively. The concrete headstocks and support piles are cut using wire cutting techniques and lifted out using the same land-based crane.
The piles supporting the 3 wharves vary in design, i.e. timber, steel, or concrete, and are removed using the same 35t crane barge used for the demolition of the “Finger” wharf. Pending on their design, the piles are extracted using either direct line pulling or line pulling combined with a vibratory hammer/clamping system.
The project also involves the demolition of a range of land-based redundant assets including old office buildings, electrical substations, and the remainder of a coal loader structure. Before demolition commenced, identified hazardous materials such as asbestos and lead-based paints were removed and clearance certificates were obtained from a licensed third-party hygienist.
The project presents several key challenges including:
- Extremely restricted workspace: the strip of land available on the actual “terra firma” is only 18m wide from the site boundary on Bridge Road to the existing seawall.
- Close proximity to stakeholders and public areas: stringent parameters were defined for key aspects of the project such as noise levels, work hours, traffic and public interactions, etc. As such, an extensive planning phase took place and detailed management plans were developed showcasing how these parameters will be met at all phases of the project. In addition, an extensive environmental monitoring program is implemented including notably day-to-day noise, vibration, dust, and water quality monitoring sampled from multiple locations around and outside of the site.
- Availability of technical information on the existing works: very little was available for the Finger “Wharf” and the information available for the “Hanson” wharf relied on 50-year old drawings, Comprehensive information was obtained for the pre-cast wharf, being more recent. To overcome the lack of structural drawings, an extensive investigation campaign was carried out during the pre-works phase including core holing of all hardstands to confirm the thickness of the concrete decks and reinforcing extent. A full geotechnical assessment of the land strip located behind the seawall was also conducted to confirm bearing capabilities and validate the use of 250t crane lifting panels up to 40t in weight.
It is expected the project will achieve in excess of 95% of all demolished materials being recycled. This includes concrete (approx. 9000 tonnes), brick, steel, and hardwood timber. The project is currently on the program with a target for completion in March 2021 and safety KPIs being met, with nil LTI or MTI incidents reported.