Completion of the Peka Peka to north of Otaki (PP2O) section of the Kapiti Expressway has, like many other large road projects in the country, faced several construction challenges for a bunch of reasons and construction costs ballooned out over extra work. Richard Silcock talks to the project director.
The four-lane 13-kilometre section of the Kapiti Expressway from Peka Peka to north of Otaki is now expected to be completed and open to traffic by late next year, almost two years later than the original date.
While it is not unusual for a road project of this magnitude to strike delays it has essentially been a change in the paving specification and the addition of a shared cycleway and pedestrian walkway that required additional consents, further design work and earthworks that have been the main delaying factors.
The shared pathway which will also include a grassed track for horses will run alongside the carriageway. This pathway was not included in the initial design and was added to the specification some 16 months after the project began in mid-2018. When completed, it will join the existing pathway of the completed 18-kilometre section of the Kapiti Expressway south of Peka Peka to Paekakareki.
Another factor accounting for the delay were the various pandemic lockdowns over the past two years that resulted in the project being closed down.
At the southern end of the project there has also been some extensive ground excavation and preload compaction work due to a peat bog which required extensive earthworks.
Chris Hunt, project director for the Fletcher/Higgins JV constructing the expressway says he is generally happy with the progress now being made given the bunch of unforeseen contributing factors and the increase in the scope of the project.
“Despite the loss of work hours due to the lockdowns(1) our construction teams were back up and running as soon as possible. They made good progress in catching up for lost time, but with the additional work required for the shared pathway and the change in the paving specification along with the strict protocols of working under Covid restrictions, it has made it impossible to meet the original completion date of January (2021) this year,” says Chris.
“Unlike some other projects in the country we did not lose our labour force overseas due to the Covid border restrictions as we (Fletcher Infrastructure and Higgins Construction) are New Zealand based so we did not need to bring in any overseas expertise. Where required we did bring in sub-contractors from the local market to increase our capacity going forward and have also brought in additional paving resources to establish a ‘super paving crew’ to increase our production capacity by 20 percent.
“So right now, it’s about being flexible with our schedules and working around the weather and the things to be completed, for example, the sub-base stabilisation, paving and asphalting, shoulders and medians, wire rope safety barriers, signage and the integration of the 10 kilometres of local roads – so there’s still quite a bit to do.
“Despite the lockdowns we have completed 90 percent of the just over 2.2 million cubic metres of earthworks required by working through into autumn and early winter, however due to the high moisture content of the ground we weren’t able to get the desired sub-base compaction, so again this has held us up.
“Almost all of the 10 bridge structures, 42 culverts and the realignment of the main trunk railway line were completed some time ago, but there is a fairly large earth embankment to be completed at the northern end, where the expressway passes over a new bridge that crosses the Waitohu Stream and joins up with SH1 near Taylors Road.
“A good proportion of the sub-base has been laid in the mid-section of the alignment and we are now moving into the paving phase in this section and would expect to have most of that completed by the end of the coming summer/autumn, weather and any further lockdowns permitting.
“Over October and November, the asphalting team was laying over 14,000 tonnes of asphalt each month and the whole expressway will require in the region of 100,000 tonnes to complete.
“There were some initial aggregate supply issues with local quarries unable to always meet the demand for high grade aggregate and this, along with the restricted working hours as a result of the lockdowns, hampered supply in the early stages of construction. We are now sourcing the asphalt paving aggregate from a quarry in the Rangitikei and the sub-base material from Winstone’s quarry here in Otaki.”
Construction of the paving for the expressway comprises 100mm of structural asphalt (AC20) over a cement stabilised sub-base with a 75mm deep-lift layer (AC14) on top, capped with a 25mm layer of epoxy modified open-graded porous asphalt (EMOGPA).
“This provides a quieter and superior road surface compared to chip seal and we expect it will provide a whole-of-life expectancy of +/- 25-30 years(2),” says Chris. “The downside lies in the actual laying of the EMOGPA as it is very susceptible to extremes in the weather.
“For example, when it is fine but frosty it is too cold to lay the asphalt. Conversely, when it is mild but overcast with rain it is too wet. When we have holdups such as lockdowns, it in-effect pushes our paving programme out into the colder, wetter winter months with more potential for holdups and this again could affect the completion date, so we are working to find ways of mitigating the impact of this.
“We have set up an asphalt plant here in Otaki specifically for this project. Having this resource close by eliminates the need to transport the material a long distance or affect traffic on SH1.”
Another factor that caused some delay due to the addition of the shared cycle/pathway was the widening of the 330-metre-long Otaki River Bridge(3) to accommodate it.
“It has entailed extending the width of the bridge by two and a half metres to 28 metres wide,” says Chris.
“There have also been some issues in getting technical specialists from our head office in Auckland through the border controls and this has again added to some delays with the requirement for exemption certification.”
A section of the walk/cycleway and grassed equestrian track at the southern end is almost complete and a team will be working on the remaining section over the coming summer.
As the expressway bypasses the township of Otaki there will be on and off-ramps for traffic heading into or out of the town at both the southern and northern approaches of the expressway.
The southern interchange will utilise the existing SH1 with traffic following the existing highway into the town via the old Otaki River Bridge. The northern interchange will have on and off-ramps just north of the town and will utilise a recently constructed over-bridge that passes back over the expressway and the main-trunk railway line to bring traffic into or out of the town.
Six large wetlands have been created along the expressway and will, together with the existing and enhanced Makahuri wetland, provide ecological mitigation through the collection and treatment of rainwater run-off(4). These have largely been completed and are in various stages of planting with native species and will be completed in autumn next year.
Planting has also taken place on the new embankments along the expressway with a mixture of flax, shrubs and native grass species and this planting will also continue into autumn.
Chris says there are a number of sub-contractors still involved in the project, including Goodmans (earthmoving), Riverside Engineering (culvert construction) along with fencing, drainage, ITS and vegetation planting crews.
Local reaction to the delay in completing the expressway has been largely muted. The Kapiti Chamber of Commerce says it will have an ongoing effect on road travel in the region with further congestion and delays.
A spokesperson for the Kapiti Coast District Council says while the delay is disappointing it is understandable given the circumstances.
“While the disruption to the local community with the ongoing delays to traffic flows along SH1 is frustrating, the silver lining is the continued employment of local sub-contractors and economic benefits that brings to the local community.”
The construction cost has ballooned out from the original estimate of $330 million to $405 million, essentially due to the extra work involved in constructing the shared pathway and the additional cost for the paving and widening of the Otaki River Bridge.
NZTA say the speed limit for this section of the expressway will be 100kmph and any changes will only be considered at a later date.
(1) The lockdowns due to Covid-19 resulted in only 350 man-hours being worked in April last year, compared to 40,000 hours being worked in April of the previous year.
(2) Deep lift asphalt costs around $190 per square metre to lay compared to granular pavement, which is around $50 per square metre.
(3) The Otaki River Bridge, at 330 metres is the longest of the 10 bridges constructed for the expressway. The second longest is the Waitohu Bridge (93 metres long) at the northern end of the project, where it joins SH1.
(4) The wetlands act as a natural filter to eliminate sediment and hydrocarbons running into the various streams that bisect the area and provide a habitat for wildlife.
Image by Mark Coote.