The Hamilton section of the Waikato Expressway is the final stretch to be constructed. Richard Silcock reports on its progress.
The 22 kilometre Hamilton section of the Waikato Expressway is scheduled to be finished by late next year (1), making it the final segment of the 102.2 kilometre long expressway to be completed.
Work on the expressway commenced with widening and upgrading sections of SH1 12 years ago at the northern-most end and has progressed in sections since, with seven (2) of the sections being ‘greenfield’ developments.
The Hamilton section, which is the largest of the seven sections, will connect with the Ngaruawahia section to the north and the Cambridge section via an interchange near Tamahere in the south.
It will bypass Hamilton City, greatly reducing through traffic in the CBD and other outer areas of the city (3).
This section is being constructed by the City Edge Alliance made up of Fletcher Construction, Higgins Contractors, Coffey Geotech (NZ) and Beca as construction design consultants under an alliance contract with the NZ Transport Agency (NZTA). Hicks Brothers Infrastructure is providing the bulk of the earthworks and Opus (now WSP), who provided the initial feasibility study and design work, is the principal advisor to the transport agency.
Higgins is responsible for delivering around 25 percent of the project including the paving and surfacing together with approximately six kilometres of local road upgrades and traffic management.
Construction started at the beginning of 2016 and is being funded from the National Land Transport Fund at a cost of $607 million.
At the time of Contractor going to print, over five and a half million cubic metres of earth had been excavated and shifted to create the alignment and bridge construction is well advanced with some already completed. Work is now moving to road construction, paving and surfacing.
Large tracts of land on either side of the expressway alignment, which were excavated to provide material for the embankments, have been contoured, topsoil applied and pasture seeded and a large retaining wall utilising ‘H’ beams is being built for the purpose of constructing a shared walking/cycling path between the city and Tamahere.
The Transport Agency’s principal project manager for this section, Jo Wilton, says this is the most challenging, most complex and diverse section of the expressway as it entails constructing five interchanges, 17 bridges, large box culverts, high retaining walls and several new connecting roads.
“Some construction work has also involved working alongside, or above ‘live’ sections of SH1, particularly around the southern interchange,” she says.
“It included switching SH1 traffic across different alignments over six separate progressive stages of construction. This was a challenge in itself as it required critical traffic planning and management.
“While this interchange only has south facing on-ramps, it also entailed constructing two bridges and some pretty substantial MS retaining walls.”
Of the 17 bridges along this section, 10 will carry local roads over the expressway, four will take it over local roads and three will cross over deep gullies at the southern end. One of the overbridges also passes over the main Hamilton (Frankton) -Tauranga railway line just north of the Ruakura interchange.
The three deep gullies and streams are being bridged rather than filled to alleviate disturbance to environmental habitats.
“As these waterways and gullies are the habitat of native long tailed bats, copper skinks and eels, during construction of the bridges and culverts these species were temporally relocated and particular care taken in planning plant restoration,” says Jo.
The highest bridge (4) passes over the expressway at a height of 18.8 metres and the longest passes over the Mangaonua Stream near Ruakura at a length of 150 metres.
The bridges are mostly of concrete beam construction. The longer ones utilising prefabricated steel beams and concrete super-Ts, decking and abutments. The up to 68 tonne steel beams were supplied by Eastbridge and trucked to site from Napier, with all precast supplied from the HEB and Wilson precast plants in the area.
Three of the bridges will feature local Maori art inspired panels on the angled abutments beneath the bridges and depict the cultural significance of Matariki.
Alliance project manager Matt Fairweather says the construction of the bridges presented some complex engineering challenges due to the high water table and perched aquifers.
“For the gully bridges we had to first drain the ground water and then stabilise the ground by compaction, soil nails in the banks and utilise a combination of CFA, screw and driven piles to a depth of 60-metres for the concrete foundations,” says Matt.
“In the flat sections, where the water table can be less than one metre below the ground due to the proximity of the Waikato River and various streams and swamps, we could only work over the summer months, as the water table rose considerably in the winter due the higher rainfall.
“For the highest bridge, the curved Kay Road overbridge, 144,000 cubic metres of earth was excavated from under it where it passes through a cutting and 32 piles were driven 20 metres into the ground for the foundations of the two, 15 metre-high piers.
“Due to the traffic volumes predicted for this section of the expressway and to mitigate pavement deterioration the paving will be laid to Hi-lab specification, cement stabilised and surfaced with ‘stone-mastic’ asphalt to M10 standard.
“Hi-lab paving can be more challenging to lay than traditional road paving, so we had experienced operators train our people and also hired some additional skilled operators from the Philippines,” says Matt.
“The procedure for laying Hi-lab begins by first grading and compacting a layer of sand. A subbase, comprising a blend of rock, from 65mm down to 5mm fine material is spread on top of the sand, trimmed and rolled to level.
“A layer of cement is then spread on top and a mechanical hoe mixes it all together with water before it is further compacted using vibrating rollers.
“The next layer – the base course is blended from a smaller 40mm rock down to fine material and is laid in the same way as the subbase. Chipseal is then laid followed by a layer of stone-mastic asphalt.
“The depth of the various layers is important and the whole procedure is very time critical as it must be completed in a continuous process.”
Most of the rock is being sourced from quarries in Huntly and Tokoroa and every step in the process is subject to strict quality control assurance tests to ensure the pavement is constructed to the required standard as specified by the Transport Agency with some 100,000 quality assurance tests carried out so far.
The agency says Hi-lab will provide a smoother, longer lasting pavement and the asphalt surface will help reduce road noise and minimise sound reaching some nearby suburban housing. In addition, noise walls may be constructed where appropriate.
Around 650 people are involved in the construction of this section, with some recruited from overseas due to skill shortages as a result of other large road projects currently under construction (5).
Longswamp and Huntly sections now completed
The 5.9-kilometre Longswamp section, connecting with the Meremere and Rangiriri sections has seen the existing SH1 carriageway widened from two to four lanes, repaved and central and side safety barriers installed.
The 15-kilometre, Huntly ‘greenfield’ section was opened to traffic on March 9. It bypasses Huntly to the east, crossing lowlands and swamps and cuts through the Taupiri Range via a 400-metre-long, 57 metre cutting, and connects with the Ohinewai and Ngaruawahia sections.
Other features of this section include the giant artworks alongside the carriageway that depict waka, pou and a giant eel trap. Construction was carried out by Fulton Hogan, HEB, Jacobs, and Opus/WSP (as design consultants) in a joint venture that took four and a half years to complete at a cost of $384 million. (Refer Contractor, March & April 2020).
- Physical works on the project were shut down due to the pandemic on 25 March and resumed again under Alert Level 3 on 28 April. It is expected this may have an impact on the completion date, however the Transport Agency says this won’t be known for some time.
- There are 11 sections that make up the expressway: Four incorporated existing and upgraded/widened sections of SH1. The seven sections referred to are new ‘greenfield’ alignments.
- SH1 currently passes through the western suburbs of Hamilton, one of the fastest growing inland cities in the country with a population of around 175,000.
- For more details on the Kay Road overbridge – refer Contractor, December 2018.
- For example, up until the L4 lockdown the Transmission Gully Motorway, Kapiti Expressway (PekaPeka to Otaki), Puhoi to Warkworth Motorway, and Christchurch Southern Motorway accounted for a workforce of over 2000.
Facts about the Waikato Expressway:
- The four-lane, 102.2 kilometre Waikato Expressway, which extends from Bombay to just south of Cambridge, will be the key transport corridor for the Waikato region – connecting Auckland to the agricultural and business centres of the Waikato and the Bay of Plenty.
- The seven ‘greenfield’ sections of the expressway were constructed under differing contract models as design, funding, land purchase, public consultation, tendering and contractor appointment was finalised at a cost of $2.2 billion.
- The Cambridge section of the expressway has a speed limit of 110kph, all other sections, including the Hamilton and Huntly sections are designated100kph.
- Any future increase to the speed limit is subject to consultation, safety audits and legislation.
- It is estimated up to 25,000 vehicles are expected to use the Waikato Expressway daily.
- Travel times are expected to be reduced by up to 30-35 minutes between Auckland and Hamilton.
Credit: NZTA/Grant Hubbard Photography