A giant crawler-crane was used for constructing the longest bridge on the Kapiti Expressway. RICHARD SILCOCK checks out the engineering challenges and some stats on the crane.
ONE OF 18 BRIDGES along an 18-kilometre section (MacKays to Peka Peka) of the Kapiti Expressway, the 182-metre, five-span, ‘twin-bridge’ over the Waikanae River and the adjacent flood plain is the largest single structure of the entire expressway project.
The bridge has been architecturally and seismically designed and is claimed to have pushed bridge engineering design and innovation to new limits in New Zealand. Each of the two separate ‘twin-bridges’, one for each direction of travel, will carry two lanes of traffic and incorporate a central median barrier and a hard shoulder.
The expressway and associated infrastructure is being constructed by contractors Fletcher Construction and Higgins Contracting (now a part of Fletchers) and engineering consultancy Beca, which together with the NZ Transport Agency (NZTA) comprise the Mackays to Peka Peka (M2PP) Alliance. Goodman Contracting, as a subcontractor, is doing the majority of the earthworks and the local council is a non-commercial partner in the Alliance.
Work on the $23 million, eight-metre high Waikanae River Bridge started in April 2014 and is expected to be completed later this year.
“With the present rate of progress, we expect to have this structure completed by October,” says John Palm, the Alliance’s newly appointed project manager.
“The entire expressway itself is scheduled for completion in mid-2017 but we are currently ahead of time, so if we can keep up our current rate of progress, the expressway could be ready for use by January or February next year.
“For the Waikanae Bridge, we’ve completed the earthworks, bridge piers, sub-structure and have all 55 Super-Tee beams in place,” says John. “We are currently building the concrete decks and will soon move on to constructing the traffic barriers.
“Due to the width of the flood plain, which is subject to large volumes of water coming downstream during periods of heavy rain in the headwaters on the eastern side of the Tararua Ranges, and so that we could achieve a 38-metre clear span over the actual river, we had to use 1825mm Super-Tee beams,” says John.
“These are the longest and the heaviest Super-Tees to be cast in New Zealand, with each weighing up to 95 tonnes.
“The pre-cast concrete beams are 39 metres long so lifting and transporting them to the bridge site required truck and trailer transporters capable of carrying the beams from our pre-casting yard at Otaihanga some three to four kilometres away and a giant, 400-tonne crawler-crane to lift and accurately place them in position.
“This required meticulous planning and highly skilled crane operators, as the bridge site is quite difficult and tight,” he says. “The crane was also used to lift the 150 tonne precast crossheads beams into place on the bridge piers.”
The 400 tonne, heavy lift Liebherr crawler-crane was shipped from Europe to work on the project. Due to its size, 25 heavy transporter trucks were required to bring the various crane parts from the port in Wellington to the Kapiti Coast site for assembling. The crane, which is powered by a Liebherr six-cylinder diesel motor, has a boom extending up to 119 metres at maximum reach and moves on a continuous caterpillar steel track.
“To place the bridge beams the crane was set up with a standard counterweight of 135 tonnes, however to place the beams over the river itself, the crane required a further 230 tonnes of suspended counterweight to counterbalance and increase the lift capacity,” says John.
A wide access track down to the river was constructed to allow the crane to reach the site on the southern bank of the river and a reinforced pad was built for it to sit on so that it would not sink into the soft ground.
The crane was also used in the construction of another expressway bridge over Te Moana Road, Waikanae, before being moved back to the river site for the lifting of beams from the northern river bank.
“The bridge has been constructed on mono-piles which are three-metres wide and bored to a depth of 40 metres [believed to be the biggest bored piles in New Zealand] due to the composition of the ground which comprises sand and silt and a high water table,” says John. “To combat this there has been significant ground improvement and compaction carried out in the form of stone columns under the bridge abutments (see Contractor November 2015).
“Due to the size and weight of the 60 tonne, pile reinforcing silo-like cages that were used in the pile foundations to strengthen the bridge piers, special lifting clamps and bracing spreaders had to be designed and fabricated to ensure the reinforcing cages did not buckle when installed into the pile casings.”
The Waikanae River Bridge has been designed to withstand 100-year floods and a one-in-2500 year earthquake. A shared cycleway, walkway and bridle-path, which travels the entire length of the expressway, will also be included, and the concrete fascias on the bridge piers will feature Maori designs which have been developed in collaboration with the local iwi, Te Atiawa.
When completed, the bridge will have used 7300 cubic metres of concrete, and over 1850 tonnes of certified steel reinforcing.
The 33-kilometre, $630 million Kapiti Expressway, which will run from Mackay’s Crossing, near Paekakariki to just north of Otaki will form, along with the Wellington Motorway and Transmission Gully, the Wellington Northern Corridor and is classified as a Road of National Significance (RoNS).
According to NZTA, the Kapiti Expressway and the bridges along it will constitute one of the most technologically and environmentally advanced road projects constructed in New Zealand.