Construction of the $630 million, four-lane Kapiti Expressway is forging ahead and despite technical challenges and a very wet winter contractors are rejoicing over progress. RICHARD SILCOCK reports.
DESPITE THIS WINTER being one of the wettest and coldest, with extreme weather in the area (115mm of rain fell in just one day during May), work on an 18-kilometre section of the 33-kilometre Kapiti Expressway is well advanced with those involved reported to be “rejoicing over the phenomenal progress”.
The NZ Transport Agency, with contractors Fletcher Construction and Higgins Contracting, and engineering consultancy Beca together form the M2PP Alliance constructing this section of the expressway. Goodman Contractors, as a subcontractor is doing most of the earthworks and the Kapiti Coast District Council (KCDC) is a non-commercial partner in the Alliance.
Snaking its way north through the Kapiti Coast on the south-western flank of the North Island, this grade-separated RoNS expressway will run from MacKay’s Crossing near Paekakariki to just north of Otaki. It will join with the Transmission Gully Motorway once that is completed in 2020 at MacKay’s Crossing, giving an uninterrupted route from Wellington to Levin, replacing the existing SH1 as the main ‘Northern Corridor’.
A section, from MacKay’s Crossing to Peka Peka was started in December 2013 and is expected to be completed by mid-2017. With specimen design almost complete, the Peka Peka to Otaki section should go out for tender shortly with construction expected to start by mid next year and be completed by 2020. A new section of highway from Otaki to Levin is at the early concept design stage.
John Palm, the Alliance’s construction manager, says the project has progressed very well and with summer approaching construction momentum is moving up a notch.
“At the end of October 80 percent of the earthworks were complete and 11 of the 18 bridges are nearing completion,” John says. “We have relocated the main natural-gas pipeline and some utilities and are well advanced in constructing 14 hectares of engineered wetlands, some of which provide for stormwater retention. In places we have also completed paving work and the planting of around 1.5 million natives along a vegetation corridor is advancing well.”
“It has not been without some civil engineering challenges,” says John. “One of our biggest challenges has been building the expressway to withstand a 1-in-2500 year major earthquake and a 1-in-100 year flood.
“Due to the proximity of multiple fault lines and the ground composition, which comprises sand, peat, soft subsoils and river silts, along with a high water table and a number of natural wetlands, much of the ground is prone to movement, liquefaction and flooding.
“As a result, work has involved a range of engineering techniques to strengthen and compact the ground. This included pre-loading sections of the alignment for 12 months and utilising dynamic compaction around bridge foundations which involves dropping a 13-tonne weight a number of times from a crane, with the impact and vibration creating compaction.
“Concrete lattices are also being built to interlock the bridge piles. These form a framework that helps lock the ground in place during an earthquake.”
Another technique being used is the construction of stone columns, which are built by filling bored holes with rock and then vibrating them. A number of columns arranged in close proximity compact the surrounding ground and also allow drainage.
As the expressway traverses both ‘green-fields’ and urban areas a lot of the carriageway is being built above bisecting local roads and around the urban areas by way of bridges and compacted earth embankments.
For reasons of efficiency the bridges, with the exception of the one spanning Ngarara Road in Waikanae, have been constructed on mono-piles which are three metres wide and bored to a depth of 40 metres.
T52 H-piles, which allow for severe ground movement, are also being used to provide additional support for bridge abutments which are further stabilised by mechanically stabilised earth walls. These walls are constructed by compacting sloping layers of reinforced grid fabric and earth around the piles to form a supporting bank at each end of a bridge.
Due to the size and weight of the 60 tonne, iron-reinforcing silos that are used to strengthen the concrete of the bridge piers, special lifting clamps and bracing spreaders had to be designed and fabricated to ensure the silos did not buckle when installed into the pier and pile casings.
The piers are topped with pre-cast concrete crosshead beams, some of which weigh 180 tonnes and are the heaviest precast beams produced in New Zealand.
“By building a ‘family’ of bridges, efficiencies are gained as it allows beams and crossheads to be precast to a standard size at our on-site yard at Otaihanga,” says John. “This has avoided significant false work on site and minimised the hazards of working over ‘live’ roads and rivers.”
Most of the bridges at the southern end are almost complete with re-alignment and paving of the roads under each expected to be completed shortly as are the double roundabouts at Poplar Avenue and Peka Peka where the expressway converges with the existing highway.
Construction of a new bridge over the Waikanae River is well advanced. It is six spans, 180 metres long, and is the longest for this section of the expressway. While the river could be bridged in a single span, the additional spans allow for large volumes of water coming down the river during periods of heavy rainfall.
Work on the columns and crossheads for the bridges over Kapiti Road and Te Moana Road is also well advanced with the on/off ramps expected to be completed by Christmas. An interchange is also being constructed at Kapiti Road which will be upgraded to four lanes to provide for increased traffic flows.
The bridge at Ngarara Road is being constructed using a top-down method and is the only bridge the expressway will pass under. Construction has involved boring 56 piles to a depth of 30 metres with the abutments mounted by 30-metre T-beam spans. The reinforced concrete floor slab effectively braces the structure.
The two curved footbridges over the expressway, one at Raumati and the other at Paraparaumu, were jointly designed by architects Warren and Mahony and Monk Mackenzie to provide an east-west connection for pedestrians. They will have a “sinuous sculptural look” and be finished in high-gloss black steel, evocative of the native eels found in the rivers. Lighting by way of LEDs will be incorporated in handrails and poles.
A double retaining wall just south of Waikanae is being built to allow the alignment to skirt a historically significant Maori reservation. The concrete wall will be 90 metres wide along the lower wall and 12 metres high in total and will feature cultural icons on the concrete panels.
Along with engineered wetlands, swales have been constructed on either side of the expressway to cope with excessive rainfall run-off or flood events, and a three-metre wide cycle/walkway and bridle-path will run the entire length.
Goodman Contracting, which has been responsible for most of the earthworks, won the contract due to its knowledge of the ground conditions. Managing director, Stan Goodman, says the earthworks have amounted to just under three million cubic metres of earth, peat and sand being moved.
“This has included the removal of sand hills, excavation of peat to below the water table, filling excavations with sand, building large earth bunds and embankments, along with carriageway formation,” says Stan. “This work has been aided by the use of in-cab, 3D GNSS/Cloud-based survey positioning equipment, which has allowed us to work rapidly with a high degree of efficiency and accuracy.”
Goodman has 40 CAT excavators and heavy bulldozers, 36 Volvo dump trucks, elevating scrapers and a number of rollers and graders working on site.
Higgin’s spokesperson for the Alliance, David Rubery, says safety is paramount as the project involves over 650 people.
“The project won the Site Safe Award for Innovation last year in recognition of ensuring the health and safety of workers, visitors and the community,” says David. “This is a great achievement for a project of this magnitude.”
The expressway has not been without its critics with some saying it will spoil the beauty of the coast and cut communities in half. Property owners affected by the expressway route tried to stave-off the expressway running through or close to their property and advocated for a connecting ‘link road’ instead. Others took their case all the way to the Supreme Court which, after ordering some slight adjustments to the proposed alignment, found in favour of the Transport Agency.
This expressway project is one of the first to include a council body as part of an alliance and has, according to John Palm, brought about a partnering attitude, collaboration, and a ‘no surprises’ approach for councillors.
“In particular, the council allowed us to work through changes in consents and provided a ‘heads-up’ on pending issues that have impacted on various communities and individuals,” says John.
KCDC mayor, Ross Church, says they’ve been fortunate to have a dedicated group of professional contractors on board who show a caring and respectful attitude towards the community, who are always ready to listen to the concerns of residents and respond appropriately.
The establishment of a community liaison team along with informative site tours, updates in local papers, monthly online newsletters, a hot-line and letterbox drops has kept the public well informed, and where traffic has been disrupted at crossing points of local roads, effective controls have pretty much met with public tolerance.
John Palm says the focus for the coming summer months will be to complete the earthworks and bridges, get the bulk of the pavement down, construct culverts and kerbing, continue with the planting programme, and later in the year rehabilitate two kilometres of existing highway north of MacKay’s Crossing that has suffered sinkage undulations and surface deterioration.
According to NZTA, the expressway will be one of the most technologically and environmentally advanced road projects constructed in New Zealand.