Image: A Goodman’s CAT 374F excavator shifting tonnes of soil at a time near a residential area – near the alignment.
After 12 years of planning, deliberation and changes in Government transport policy, the long-awaited Otaki to north of Levin Expressway (O2NL) is forging ahead, with a fast construction strategy in place and earthworks now underway writes Richard Silcock.
Two construction alliances are building this 24-kilometre-long O2NL Expressway that will connect with the existing Peka Peka to Otaki Expressway just north of Otaki at the southern end and SH1 just north of Levin at the northern end – to complete what is known as the Wellington Northern Corridor.
In order to fast-track the construction, the alliances are working on the project from opposite ends. Fulton Hogan, HEB, WSP and Aurecon are designing and constructing the northern section from Levin to north of the Ohau River and Downer, McConnell Dowell, Beca and Tonkin & Taylor will be delivering the southern section from Otaki to the Ohau River. Each alliance is responsible for constructing approximately 12 kilometres.
The two alliances will work with the client and its project partners: the Transport Agency, the Horowhenua District Council and local Maori communities such as the Muaupoko Tribal Authority, to deliver the project as quickly as possible.
Project director, Glen Prince, says the separated four-lane O2NL Expressway will run to the east of the existing SH1 in a north–south direction, bypassing the townships of Manakau, Waikawa, Ohau and Levin and comprise an asphalted carriageway and a number of structures. These being: four bridges, two underpasses, 70 culverts, two interchanges and two roundabouts.
“By having our two alliance teams working at each end of the project along with our earth-moving sub-alliance partner Goodman’s, all of whom are very familiar with the topography and geology of this area having been involved in constructing other sections of the corridor, we will be able to fast-track the construction period and bring savings in cost to the project,” says Glen.
“Each team was contracted separately, but they are all working under what we call a Joint Interface Management Plan (JIMP) with an alliance manager responsible for each team and construction output.
“All up, we presently have around 500 staff on-site, including the earthworks team, and this will ramp up as we progress the project over this year and next.”
The manager for the southern alliance, Hugh Milliken, says approximately 4.5 million cubic metres of soil and material are expected to be handled throughout the project.
“The earthworks started in October last year and good progress has been made over this summer-autumn period with Goodman’s bringing in some very large equipment, including a number of huge earth-scrapers that they used on the new Ashhurst to Woodville (Te Ahu a Turanga) section of SH3 over the Ruahine Ranges,” says Hugh.
“These machines are capable of shifting 40 tonnes of soil at a time, and with the recent good weather, around 14 kilometres of the future alignment is currently being worked on.
“There are a number of shallow gullies and small streams in the southern section which we will earth-fill and build culverts for these, with the largest culvert being a five-barrel, reinforced concrete structure to allow the Waikawa Stream to flow under the Expressway.
“There is some diversity in the soil structures across the length of the project, with the northern section mainly alluvial gravels and silts, while the southern section is predominantly a mixture of gravel, Mesozoic sandstone and sand.
“Fortunately, unlike the Kapiti Expressway to the south, there are no peats or swamplands, so there should be no need for deep excavations and extensive pre-loading (compaction) or the drainage of wetlands.”
The alignment will cross the Ohau River which flows from the nearby Tararua Ranges and a 200 metre-long, Super-Hi girder-constructed five-span bridge will be built by the northern alliance team.
Tony Adams, manager of the northern alliance says the Ohau River Bridge will be the largest structure built for the project with construction beginning later this year.
“We are currently building temporary staging for this bridge and want to get it in place as soon as possible as it will help provide access for our teams working on the project and alleviate the need for trucks and other heavy equipment using SH1 to cross the river,” he says.
Several smaller bridges will also be constructed, with one crossing the main trunk railway line and another providing access to Manakau Heights, a residential development on the eastern side of the Expressway. The earthworks to construct the bridge abutments will use material excavated from sections of the alignment.
With the exception of the shallow gullies at the southern end most of the alignment will traverse flat land with only a few small undulations. Several small cuttings may be required, but these are not expected to present any particular construction challenges.
Following a slight realignment, the Expressway will now skirt around the Ohau Quarry that would have faced closure had a previous alignment gone ahead.
Glen says that while most of the earthworks will be done over the spring to autumn period, the weather can at times upset schedules and contingency plans are in place to minimise any such disruptions. It is expected some earthworks will continue over winter.
The carriageway will be constructed using a granular subbase-course and an epoxy-resin structural asphalt surface layer to provide a smooth and quiet driving experience. All of the aggregate required for the project will largely be sourced from local quarries and the nearby Manawatu–Rangitikei region.
This project is the northernmost stage of the Wellington Northern Corridor (WNC) which began in 2012 with the construction of the Transmission Gully Motorway that joins the Kapiti Expressway at Paekakariki, which in turn connects to the Peka Peka to Otaki Expressway at Peka Peka, just north of Waikanae.
When the O2NL Expressway is completed, the WNC will provide just under 100 kilometres of uninterrupted carriageway from Wellington to just north of Levin, benefiting the economies of the fast-growing Otaki and Horowhenua regions and their local communities.
“The highway will deliver a more efficient and safer road and help further the growth and development of one of the country’s fastest growing regions,” says Glen.
The $2.13 billion fast-tracked O2NL Expressway is expected to be completed towards the end of 2029 and is anticipated to be a user-pays, tolled stretch of the Northern Corridor.
The cost to deliver the project includes the acquisition and purchase of land and 168 private properties, including a number of farms, several kiwifruit and blueberry orchards and 53 houses that have either been relocated or demolished.
At the time of Contractor going to print, the Iran/USA/Israel war was disrupting the supply of petrol and diesel – a factor that may influence construction going forward.