Customer: Waka Kotahi NZ Transport Agency
Location: Auckland, New Zealand
- The new bridge will be over 260m long and eight metres wide
- Main span is on a horizontal curve with a 136m radius
- The bridge’s most stunning feature is a 60m steel tied-arch
- Two southern approach spans are 12m wide creating dedicated fishing bays
- The northern and southern abutments consist of 1.2m wide reinforced concrete blade walls
- The new bridge provides up to eight meters clearance for vessels during low tide, to increase access to the upper harbour
- The replacement bridge will be a shared public space with a gentle slope to provide easy access for many users
McConnell Dowell was awarded the contract for the Waka Kotahi NZ Transport Agency project to deconstruct the Old Māngere Bridge and construct a new and improved replacement bridge to connect the communities of Onehunga and Māngere Bridge in September 2019.
The demolition of the old bridge and work to construct the new bridge will occur simultaneously and take place from both sides of the harbour. The project is scheduled to be completed in 2022.
The Old Māngere Bridge Replacement is a high profile and extremely complex bridge construction and demolition operation in a sensitive marine area. The challenges of the project are focused on two main areas, working at heights and over water. The high visibility and interest of the public in the project and especially the environmental and health and safety outcomes makes these two key areas of focus.
One of the technical challenges is the deconstruction of the Old Māngere Bridge, which was closed for public safety reasons in 2018. The demolition work will be completed using a ‘cut and crane’ method at either end of the bridge, almost in the reverse of how it was constructed over 100 years ago. In the centre section over the harbour the project team will use a barge mounted excavator to remove the spans.
Construction of the new 260m long bridge, with its show-stopping 60m central arch in structural steel will be carried out from both sides of the harbour. Temporary work platforms are being built out into the harbour from the old bridge abutments to provide access and enable the team to construct the piles, cofferdams and other structures required for the new bridge.
Careful stewardship of the Manukau Harbour is critical to the success of the project and McConnell Dowell together with the Transport Agency project team, is committed to delivering better than expected environmental outcomes.
The team are also working closely with Mana Whenua, who along with receiving regular updates on progress are also invited to visit site to conduct cultural monitoring and advise the team on appropriate safety and environmental protection measures.
Two examples of the controls in place to protect the Manukau Harbour, local flora and fauna include a large ‘net’ to prevent debris from falling into the water below and underwater noise monitoring to help manage the impact of piling.
Wherever possible we are reusing and recycling to minimise our environmental footprint. Parts of the old bridge will be salvaged so they can be used in the landscaping around the new bridge as a link to the past for future generations.
We are also reusing steel for the temporary staging from a previous bridge build in the South Island. The production of steel is a carbon rich process so recycling and reusing it is an effective way to minimise the project’s carbon footprint.
The Key to Success:
The Transport Agency has maintained a strong community focus from the early engagement and consultation through to the construction phase.
Maintaining the connectivity and accessibility around the old bridge while work is underway is important because there are two popular community assets on either side of the harbour next to the construction sites. There is the walking and cycling path on the northern side, and the causeway to the boat ramp and Waterfront Reserve on the southern side.
We developed the traffic management plan in consultation with local board members, cycle advocacy group Bike Auckland and the harbourmaster to ensure that we maintained safe access around the construction sites.
Space was limited so we minimised risk by creating separate areas for construction traffic and the public.