IN SIMPLE TERMS, the SH20A (Auckland) to Airport upgrade involves turning a current expressway standard intersection into a motorway standard one.
A lot of readers will be familiar with the Kirkbride intersection on SH20A as it guards the entrance to Auckland Airport and it can feel as if your birthday has come and gone waiting for a signal light to turn green.
Construction has already started on the $140 million project, which won’t be completed until early 2017. It involves constructing a trench for traffic in both directions on SH20A to pass underneath Kirkbride Road and separate motorway and local traffic. It also involves constructing Watercare’s Hunua 4 watermain across SH20A at Kirkbride Road, which will be done at the same time as the road works.
Provision is being made for future bus shoulder lanes, along with enhanced stormwater drainage and treatment.
As 75 percent of the country’s visitors arrive through Auckland Airport, a lot of work has also gone into the landscaping and urban design of this project, which was fast-tracked in 2013 to improve transport routes that are critical to national growth.
The project is being built by the MHX Kirkbride Alliance, made up of the NZTA, Beca Infrastructure, Fletcher Construction and Higgins Contractors – the same team that delivered the SH20 Manukau Harbour Crossing project in 2010, and the SH20 Walmsley Road upgrade in 2011.
In addition to being a ‘gateway’ for airport traffic, the project site is close to community neighbours that include a school, businesses and even homes. While the construction is being managed around this, much thought has gone into the final design in the likes of the trench retaining and noise walls.
Unique challenges and solutions
The location of critical services is creating a challenge for the project team. For example, power and data feeds linking to the Mangere Wastewater Treatment Plant and Auckland Airport run across the alignment of the trench. These feeds need to be temporarily relocated before construction can begin.
Service relocation will have an impact on traffic flow and the team is working closely with the airport and the service providers to come up with a sequence of work that best manages the flow and transitions. Directional drilling techniques are also being used which will reduce disruption to the road.
Temporary traffic management
Bluetooth traffic nodes have been installed across transport routes within the project area. This BlipTrack monitoring will provide live traffic volume data from the network so the team can monitor detour routes and make changes if required.
Digging through six to eight metres of peat to construct the trench creates technical challenges for the team. The soil composition means large plant can’t be placed on top of the peat to dig. It will have to be placed outside and reach a distance to dig, or smaller plant will have to be used. The peat makes construction of the diaphragm wall more challenging. Finding a suitable site to dispose of the peat creates another challenge. It is not much use for anything else on site.
The water table is high which creates issues with flotation, leak protection and the tension piles. The project is the largest use of tension piles in the country.
What new technology is being used?
The team is adopting a cloud-based project information management system and is currently selecting the best one to implement. It will allow mobile access to critical project information for quality and safety teams and give field access to the functions in the project office. Using cloud-based technology promotes efficiencies in document collation, particularly at the point of project hand over. Machine control is likely to be used for surveying the completed base profile.
What is the total amount of material being shifted?
The approximate dimensions of the trench are: width = 30 metres, length = 600 metres and depth = 7.5 metres at the deepest point.
Some 60,000m3 of peat is to be cut to waste; 40,000m3 of spoil is to be disposed of; and 9500m3 of concrete is needed for the base slab plus 2500 tonnes of reinforcing.
The majority of the trench retaining walls are of diaphragm wall construction, similar to the Waterview Connection approach trench. There is 6000m3 of concrete and 1200 tonnes of reinforcing going into the walls.
How is the watermain construction being carried out at the same time?
The pipe is a critical pathway and is being constructed first.
Widening work will first be undertaken on the western side of the intersection.
This will allow for traffic to be moved to this side of the corridor while the first part of the pipe is installed on the eastern side, to the point, which is now the traffic island. During this stage, widening work will also be done on the eastern side of the intersection so the flow of traffic can be diverted there, allowing for construction of the rest of the section of pipe.
How will traffic be diverted?
The on-ramps and off-ramps that run parallel to George Bolt Memorial Drive will be constructed during the second stage of the project.
Traffic will be diverted along them while the trench is built (there will be traffic diversions in place throughout the project).
Could you explain the Hunua 4 part of the project?
Hunua 4 will increase the security of the water supply to the Auckland region and cater for population growth. The new watermain will run for 28 kilometres from Redoubt North Reservoir in Manukau Heights to Campbell Crescent in Epsom, connecting to the local water supply network along the way. Ultimately, the watermain will extend through to reservoirs at the top of Khyber Pass in the city.
A significant piece of infrastructure, Hunua 4 is 1.6 to 1.9 metres in diameter and is capable of carrying up to 3000 litres of water a second.
Over 15 kilometres of watermain has already been constructed with the first 7.5 kilometres brought into service. This has increased the security of the water supply and provided additional capacity in large areas of Manukau, East Tamaki and East Auckland.
The next area to benefit from the watermain being commissioned will be Mangere; of particular note the Airport and the surrounding industrial and business areas. This connection will have been made by Christmas 2015.
No- that’s not the new runway
Adrian Littlewood, chief executive at Auckland Airport, says he is surprised at the number of people who ask him if the second runway at the airport is now under construction, as they are referring to the landscaping along George Bolt Memorial Drive close to the airport.
The nine metre high mounds of earth topped with rock are meant to create a ‘dramatic gateway’ and were designed by New Zealander and acclaimed San Francisco-based urban design adviser James Lord. The mounds are about 100 metres long and referred to as Maori stonefields. However, you can be excused for thinking they are aggregate stockpiles waiting for the crusher.
Littlewood, who was appointed chief executive in November 2012, was making a presentation to the first meeting of the Auckland branch of Civil Contractors NZ earlier this year.
While the airport with its workforce of 12,000 has spent $225 million on development work in the past four years, the second runway is actually on hold, he says.
Work did start on this runway but then the big A380 aircraft started to arrive, meaning the existing runway could handle far more passengers.
Auckland Airport is a big place and the company owns as much land as Heathrow Airport in London. Eventually a new domestic terminal will be built next to the international terminal.
Littlewood says the design work for the second runway, about two kilometres away from the existing one, is completed and current plans are for work to resume in eight years time, and with a five-year build period.
This means it will be about 2030 before Auckland Airport needs to accommodate more air traffic.
• Details supplied by MHX Kirkbride Alliance and Watercare.