What is 75m long, 5m wide and has 13,000 bolts? A Steel Multi-plate™ culvert from CSP Pacific, installed by the City Edge Alliance who are responsible for the construction of the Hamilton section of the Waikato Expressway.
The culvert has been constructed from 553 curved, galvanised metal plates and around 13,000 bolts to form the 75m long channel which carries the stream running through the bottom of the East West Gully.
When looking at options to protect the stream, while allowing an expressway to be constructed around it, engineers first considered a concrete box culvert. “A concrete culvert was initially specified but it would never have worked here as trying to excavate out a stream bed at the bottom of a gully and then having to pour these concrete sections would have been almost impossible not to mention costly,” said Richard Langley, Alliance Construction Site Engineer. “It’s like slop in places and a bridge would have been far too expensive. CSP Pacific’s Steel Multi-plate™ was the best option for this location.”
At a diameter of five metres it is the larger of the two being built to carry gully streams under the new road. “The reason for the large diameter is to allow for a 1 in 100 year rainfall event,” says Richard. “It also has to allow for a meandering rock channel in the bottom of the culvert to create a habitat suitable for native koura and fish.”
The culvert was assembled on site by bolting together pre-formed galvanised steel plates. Richard and his team were careful to maintain the cylindrical shape of the structure to firstly ensure everything fitted together and to also ensure its strength.
It took a team of eight six weeks to install the culvert, whist navigating several challenges including a tight site, installing 13,000 bolts at height and controlling ground water.
Next the culvert was gradually buried in compacted sand, including 11m of sand above the structure, which has formed the embankment for the East West Link Road.
“One of our other challenges was taking into account that we were working on a site of cultural significance – there is a Maori Pa site on one of the ridges above the gully,” explains Richard. “We also had to do a lot of work to stabilise the banks before we began excavating the path for the culvert.”
“Voytek and the team from CSP Pacific were very helpful and supportive throughout the construction of the culvert which always helps when working on something of this size.”
The Waikato Expressway will deliver a four-lane highway from the Bombay Hills to south of Cambridge. It has been built in seven sections and the 22km Hamilton section will be the final one to open. The expressway will improve safety and efficiency and reduce travel times by about 35 minutes along the 102km route.