Kapiti Expressway heads north

The second section of the Kapiti Expressway is advancing northwards with construction well underway. Richard Silcock went to check on progress.


Over the years…

The present concrete, two-lane-bridge over the Otaki River on SH1 was built in 1955, replacing a 272-metre-long wooden bridge which was built in 1901 nearer the river mouth.
Prior to that, river crossings were made by canoe or horse drawn coach through a ford in the river which was constantly subject to washout when the river was in flood. Records show a number of fatalities occurred.
The first rail bridge over the river was constructed in 1886 using timber cut from a local Totara forest. Ballast for the track was taken from the Otaki River.
The current rail bridge was constructed in 1931, as a part of the government’s plan to provide work during the Depression years.

WORK ON THE $330 MILLION, 13-kilometre, second section of the dual-lane Kapiti Expressway, from Peka Peka to just north of Otaki (known as PP2O) has, despite recent wet weather, progressed well with most construction taking place at the northern end.

Following preparatory enabling works, relocation of some utilities (water, power, gas etc) and fauna (500 eels were relocated from one waterway), clearing of vegetation and removing 31 houses along the intended carriageway (refer Contractor December 2017) physical work began in earnest last December.

This has included earthworks along the alignment, and the construction and widening of existing local link roads (SH1 traffic will temporarily be diverted to these arterial/local roads to allow contractors uninterrupted workspace). Foundations for some of the new bridges has also commenced along with preloading of the ground (peat) at the southern end.

The expressway is being constructed by Fletcher Construction under a standard NZS3916 design and build contract and delivered by an 80/20 split joint venture between Fletchers and Higgins Contractors. Subcontractors include Brian Perry Civil for the bridge piling and Goodman Contractors for the earthworks.

Fletchers has engaged BECA as head designers with Tonkin & Taylor responsible for geotechnical/storm water design and Studio Pacific Architecture for landscaping and urban design. WSP Opus is the Transport Agency’s principal advisor for the project.

This section of the expressway will connect with the completed 18-kilometre section at Peka Peka, cross-over SH1 and then follow a straight line northwards, bypassing the town of Otaki to the east, before rejoining SH1 a kilometre or two just north of the town.

Initially there was concern by local businesses that they would lose customers however these concerns have largely been allayed with the provision of local connecting roads, two ‘gateway’ roads and interchanges north and south of the township which will provide access to the CBD.

“This will provide access to the town and will also alleviate the traffic congestion currently experienced due to the volume of traffic currently passing through the town heading north/south on SH1, particularly during public holiday periods,” says the agency’s project manager for PP2O, Glen Prince.

“We established an excellent relationship with this close-knit community of just under 6000 and are getting tremendous support,” he says.

“Through a programme of face-to-face consultation, public meetings and a regular flow of information about the project, most understand and look forward to the benefits the expressway will bring to them and the town.

“Even the local secondary school has got involved, producing regular monthly videos on different aspects of the construction. They will also be helping plant some of the two million native plants along the route.”

Asked by Contractor if the new expressway will just move the traffic bottle-neck further north, Prince says research indicates that the volume of traffic drops off north of Otaki, so the expectation is this will be manageable.

Temporary steel casing for the Otaki River Bridge piling operation being lowered into position.

There will be nine new bridges constructed, the longest being a 330-metre bridge over the Otaki River (bridge 5), which is currently under construction on the southern bank, just upstream from the SH1 bridge and adjacent rail bridge.

Construction manager, Steve Findlay, says they are well advanced with the bridge foundations, with over half of the 18, 2.1-metres-in-diameter bored concrete piles now formed to a depth of 25 metres.

“The concrete piles are constructed using bentonite support (in lieu of steel casings) and incorporate plunged column reinforcing steel,” says Steve.

“The columns and crossheads will be constructed in situ and once these are complete we will install the 70-tonne concrete beams and commence the bridge decking towards the end of this year.

“With the river level low at the moment we may take the opportunity to sink another set of piles from the southern side before moving to the north bank to complete the piles and piers for the northern abutment.”

In terms of construction challenges, Steve says that apart from a few minor realignments of the initial carriageway design, the Otaki Bridge is probably their biggest challenge.

“As we are working in the bed of the river, which is prone to rapidly reaching high water level, velocity and volume as it flows from the nearby Tararua Ranges during periods of rainfall, we keep in contact with the regional council on a daily basis as they have flood warning systems in place upstream.”

The construction of steel-strapped reinforced earth abutments for a new rail overbridge at the northern end is also well advanced. The abutment panels have been pre-cast on site (refer Contractor December 2017) with the exposed aggregate panels forming part of the overall design aspect which will be repeated throughout the project.

To allow for the expressway alignment, the main trunk railway line is being relocated over a distance of 1.6 kilometres at the northern end. It will take around four months to construct the new track with the ‘switch-over’ expected to take place either over the coming Christmas period or next Easter. Fletchers, in conjunction with KiwiRail, is constructing the new track and Siemens will be responsible for installation of the signals.

As yet the final pavement surface is still to be decided, but will be determined by traffic data and noise modelling results in line with the consent conditions.

Aerial view looking north over the Otaki River towards the township of Otaki, with the SH1 road bridge on the left, rail bridge centre, and the piles for the new expressway bridge on the right.

It is expected this new section will cater for around 18,000 vehicles per day and open to traffic by the end of 2020 – providing in total 31 kilometres of uninterrupted four-lane expressway from Mackays Crossing, near Paekakariki (where it will join the Transmission Gully Motorway) to north of Otaki.

Symbolic cut out figures indicating a pathway for children – part of the safety strategy during construction.

There will also be a 10-kilometre purpose-built shared walking/cycle/bridal track alongside the expressway.

“It will be of a similar design to the completed section of expressway (Mackays Crossing to Peka Peka) and will link with the QE Park cycleway,” says Prince.

“It will include landscaping, bridges and underpasses to enable walkers, cyclists and people on horses safe passage through key parts of the route.”

Consideration for extending the expressway further north, from Otaki to Levin, is currently under review by the agency, which has defined nine options for a proposed alignment. However as a result of the Labour Government’s new transport policy, this has as yet to be confirmed.

There is a strong lobby group promoting this extension, however with the government’s focus on making roads safer as distinct from building new ones there could be a case for just upgrading the existing highway at this stage.

Following an extensive review the agency is expected to report back to the government shortly and a decision made before the end of the year.

This article was first published in the August 2018 issue of Contractor Magazine. To see more photos click here.

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