With 24 million people coming and going from Auckland Airport every year, and this figure on the increase, the future proofing of the main arterial to and from Auckland’s Domestic and International Airports, and Auckland’s freight centre at Airport Oaks, is underway. The NZ Transport Agency $140m Government funded project, being delivered by the Manukau Harbour Crossing (MHX) Kirkbride Alliance involves the formation of a 580m long trench underpass to allow SH20A to pass under Kirkbride Road, creating a more efficient, safe and streamlined transport system to and from Auckland Airport.
The congested signalised intersection at SH20A/Kirkbride Road is particularly heavy during peak travel periods, creating significant delays to traffic travelling to and from the airport. Auckland’s population is also expected to grow by 1 million people over the next 30 years, which would place additional pressure on the current roadway. Safety issues are another contributing factor for the fast tracking of this project as the current road layout, with the intersection, ranks as the 100th most dangerous intersection in New Zealand.
Construction on the upgrade started in 2015 with Firth awarded the concrete supply by the MHX Kirkbride Alliance. “We worked closely with the Alliance team to supply all the specialist mixes for the second Manukau Harbour Crossing which was completed in 2010, plus Firth has supplied other similar infrastructure projects in Auckland - the Waterview Connection project and the Victoria Park Tunnel,” explains Jamie Frew, Regional Operations Manager - Auckland for Firth.
“Reliability of concrete supply is key to the success of the trench construction – with over 20,000m³ of concrete in the D-Walls* and base slab, having a ready mix supplier that can reliably and consistently deliver on their promises is hugely valuable,” says Hunter White, Structures Project Engineer for the MHX Kirkbride Alliance. “Firth really stepped up to the mark here and showed great commitment by participating in our weekly last planner sessions.”
“There have been about 10 different mixes used on the project with the two most common being a 40MPa tremie mix for the Diaphragm Walls (D-Walls) at 210 slump which are now all completed, and then there is a 50MPa mix for the base slabs,” adds Jamie. “There has been 56 pours for each of the D-Walls which were around 130m³ each. We have also completed seven base slab pours which ranged from 200-350m³. We have about 35 more of these pours to go.”
Historically large concrete pours start very early to avoid peak traffic and to allow scope for the Firth teams to handle everyday work. “Unfortunately due to consent constraints we haven’t been able to start before 7.30am which has been especially challenging for the large slab pours,” says Jamie. “We have used several of our plants from around the city to ensure supply is uninterrupted. Most of the supply has come from our Penrose, East Tamaki and Wiri plants.”
Once completed, the project will improve journey time, reliability to and from the airport, accessibility to the airport, freight movements across south Auckland and it will also provide safer local connections for all road users. The project will also enable Aucklanders to fully realise the benefits of the development of the Western Ring Road, taking travellers to and from the airport along SH20A, SH20 through the Waterview Connection, SH16 and SH18, when the Waterview tunnels open in 2017.
To view a fly over video of the project click here
* Did you know that ….
When material is excavated when constructing diaphragm walls for a trench, large soil pressures are generated, which can result in the sides of the trench collapsing. D-Walls joined together like underground concrete retaining walls act as supporting structures against these soil pressures. Each of the D-Walls for this project required 26 tonne of steel reinforcing cages and about 130m³ of concrete.
The SH20A to airport project includes the following:
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Project Details
Principal: NZ Transport Agency (Transport Agency)
Main Contractor: MHX Kirkbride Alliance - NZ Transport Agency, Beca Infrastructure, Fletcher Construction and Higgins Contractors
Location: Kirkbride Road, SH20A
Product: Certified® Concrete
Before.. … after the project is completed