With the construction of the second stage of the Kapiti Expressway now underway. Richard Silcock takes a look at what’s involved.
AFTER A TRANCHE of work involving some 12 months of final design, construction planning, consents, site clearing and enabling works, the physical work for the 13-kilometre second stage of the Kapiti Expressway, from Peka Peka to just north of Otaki is now underway.
Known as the PP2O Project it will join the 18-kilometre first stage of the expressway (Mackays to Peka Peka was completed and opened to traffic in February this year – refer Contractor, March 2017) and provide in total an uninterrupted 31-kilometre stretch of four-lane highway along the Kapiti Coast.
This second stage will include nine bridges, the longest being over the Otaki River, a span of 330 metres. One point six kilometres of the main trunk railway line is to be relocated to allow for the alignment and a number of new local and arterial roads are to be constructed to provide access to and from the expressway.
Fletcher Construction and Higgins in a joint venture (JV) are carrying out the construction planning and main work, with Goodman Contracting providing the earthworks and Brian Perry Civil the bridge piling and structural work. The JV will also work closely with KiwiRail over the track realignment. The total cost for the project will be $330 million.
Design work is being done by consultants Beca, with Opus acting as the NZ Transport Agency’s principal advisor to the project. Tonkin & Taylor is providing environmental and ecological input and Studio Pacific the landscaping and urban design.
The work is being done under a design and construct contract and the Transport Agency say the JV team was chosen because they had delivered the first section of the expressway to a very high standard, within budget and ahead of the scheduled completion date while meeting environmental requirements and maintaining an excellent rapport with the local communities.
This new section of expressway will follow the existing SH1 route from Peka Peka north to Te Horo before breaking new ground to cross the Otaki River over a new bridge and bypass the township of Otaki to the east before reconnecting with SH1 to the north of the town.
Project director for the JV, Andy Goldie says they will have upwards of 300 people working on the project.
He says their main focus at this stage is north of the Otaki River where vegetation clearance, house removals (some 20 houses were either relocated or demolished) is pretty well complete.
“We’ve started on the bridges that will cross over the railway line,” says Andy. “This needs to be done because we need to move the track north of the Otaki Railway Station (the historical station will remain in its current position) to the west to allow for the new alignment.
“The earthworks have also commenced for the new rail corridor and the Goodman’s team will work through the summer period to maximise the good weather and get this work done,” he says.
“The most significant part of the project is likely to be the construction of the Otaki River Bridge. Work has commenced with earthworks, ground improvements and bored piles being driven to a depth of 25 metres for the foundations.
The 10-span bridge will comprise of 100 bridge beams, 18 insitu concrete columns and a concrete deck slab.
“We can expect some challenges as we progress the expressway but nothing too unusual from a civil engineering perspective,” says Andy. “Building the bridge over the Otaki River could present some challenges as it will be constructed within the riverbed and carry the risk of the river flooding and inundating works. Mitigating this risk will be achieved by accelerating the construction and staging the work so that all ground level work within the riverbed is completed during traditionally low river flows.”
Other work has seen concrete, exposed aggregate RE panels being fabricated and stored in preparation for the bridge abutments at the work site near Otaki.
Geotechnical investigations indicate the ground composition over the length of the project varies from sand, river gravels and alluvial topsoil to some peat bog at the southern end.
Goodman has a team of up to 60 people working the site operating a range of equipment, from 40-tonne dozers, twin elevating earth-scrapers, 50-tonne excavators, and a fleet of 40-tonne dump trucks. Most of the plant is equipped with sat/nav machine control to minimise survey work.
Stan Goodman, managing director of Goodman, says they are working up to 12-hour shifts and expect to move some 1.5 million cubic metres of earth, most of which will be used for cut-to-fill or landscaping bunds.
“We expect the total earthworks for the project will take over two years to complete,” he says.
Consultation has been a big part of the time spent in preparing for the expressway. The Transport Agency, the JV and their design partners have consulted with the local councils, community liaison boards, the local community and iwi (there are five Maori hapu in the Otaki area and they are represented on the management team) and taken on board their concerns in the design, planning and resource consents process for the project.
Consultation is also taking place with interested stakeholders over the safety and traffic movement around the Peka Peka interchange and providing an improved junction for the roads leading into it, and the possibility of adding a south-bound off-ramp, and possibly connections at Te Horo.
Environmental management plans have been prepared and include provision for sediment control using silt fences and decanting bunds, dust mitigation using water trucks and wheel washes, and noise minimisation by erecting barrier fencing and squawkers.
Following the study of bird life along the Otaki River (there are dotterel breeding and feeding grounds), scouring the bush for lizards, trawling streams for eels, mudfish and inanga, and searching for rare land snails, a number of ecological controls have also been put in place to safeguard the local wildlife.
“Ahead of the diggers and other machinery starting, a huge effort has been made to find and relocate these protected native species,” says environmental manager for the project, Alice Naylor.
“Reducing environmental/ecological impacts is now a priority for road projects so care and mitigation has been an important part of our planning process,” says Alice. “For example, construction near the river will be scheduled to work around the breeding season of the dotterels and we will be creating new nesting areas upstream.
“Culverts for stream diversions are being designed to allow fish to move freely up and down streams, and old rotting logs will be relocated to provide ‘homes’ for species such as lizards and the rare snails,” she says.
“We will also be monitoring dust, noise and ground vibration to ensure minimal disturbance for nearby residents.”
In addition to this ‘all-care’ approach an extensive planting programme is planned. This will include an indigenous forest, wetland restoration, and 38 hectares of riparian planting along the length of the expressway.
With some parts of the alignment likely to pass over some areas of historical interest a team of archaeologists will work with the project team to investigate specific places of interest as the work progresses.
This section of the expressway is expected to be completed by late 2020 or early 2021. It, along with the first section and the Transmission Gully motorway which it joins at Mackays Crossing near Paekakariki (due for completion in 2020), will form part of the four-lane Wellington Northern Corridor from Wellington Airport to Levin, a distance of some 110 kilometres.
“This expressway project forms an integral part of Wellington’s Northern Corridor and has been identified as having a key role in supporting the region’s economic growth and productivity potential by cutting journey times and improving access into and out of the city and making travel to key destinations such as the airport, port and hospital more efficient,” says Glen Prince, the Transport Agency’s acting portfolio manager.
“As a part of our planning process we wanted to ensure this corridor will be resilient to disruptions like severe storms, vehicle crashes and earthquakes by constructing a robust and safe highway between Wellington and the south-western area of the North Island.”