Construction of New Zealand’s first Super•Cor™ Arch first began in 2014. Simon de Rose, Contracts Manager for Stringfellows, says, “three years later, the movement of 250,000m³ of soil, a stream diversion and significant work to complete the 1.7km realignment, and we were finally able to the demolish the 90 year old, 22m high, less than 6m wide Whakaruatapu (Skinny) Bridge.”
The old viaduct-style bridge built in 1927, named the ‘Skinny Bridge’, had been a concern for the NZ Transport Agency and locals for many years because its width of 5.79m meant it couldn’t accommodate trucks passing other vehicles … and it wouldn't stand up to a decent earthquake.
When options were being looked at for replacement for the ‘skinny bridge’ the Transport Agency considered a completely new bridge and a standard culvert option – neither were suitable due to the depth of the gully to the stream and the considerable amount of backfill which would be required to reach road level. Ultimately CSP Pacific’s Super•Cor™ Arch structure was the only option capable of carrying the fill load of 16m over the top of the culvert.
Simon and his team, with the help of CSP Pacific’s engineers, constructed the new 116m long x 6m wide Super•Cor™ Arch culvert which would eventually re-house the Whakaruatapu Stream.
The concrete trough foundations - designed by Opus Consultants in partnership with CSP Pacific - were designed to carry and spread the load of the fill through the arch culvert to the siltstone material below. The foundation is 9.3m wide, 800mm thick and contains over 1000m³ of reinforced concrete.
“From an engineering perspective the culvert has many components to it to ensure it handles the extreme weight of the 16m of fill that would go above it in various sections,” explains Voytek Wieczorek, Engineering and Technical Manager for CSP Pacific. “When looking at the photos you can see that the ribs are bolted on top of the barrel, opposite to the peaks and troughs of the corrugation. You can also see access holes at the top and bottom of the ribs, which is where they were filled with a concrete grout creating EC ribs or encased concrete ribs. Once the ribs were filled, an additional concrete foundation was poured along the base encasing the steel ‘U’ bends and the bottom of the ribs. This created the strength in the culvert enabling it to carry the extreme weight above.”
And the verdict on the completed project … in Simon’s words …
- “The back filling went really well. We didn't have any issues at all with it moving out of shape as we back filled it.
- The CSP Pacific team were really good all the way through. They rang regularly and called in when they could to check up on progress and help with any queries we had.
- The components went together really well. Everything matched and there was nothing left over - just a couple of bolts. Actually it went together far better than I thought it would.
- The Super•Cor™ was a good option for the site. It was fast and easy to put together. Being a repetitive pattern we were able to get a good rhythm going on it. Overall we were very pleased with how it went together.
- Once we completed the first 40m of the 116m culvert we were able to torque the bolts and start back filling that section, while the construction of the rest of the culvert continued. The beauty of the Super•Cor™ is that as soon as you've completed three consecutive rings you can torque the bolts. This very important when you need to cart fill from one side of the site to the other.
- Another huge advantage of this project was the size of the construction equipment we used on site. We only needed a 25 tonne crane for the whole project whereas with a bridge or a culvert construction we would have needed a 100 or 200 tonne crane. In looking at the gully and site, where space was constrained, it would have made things so much more difficult. We also didn't need to build huge crane pads.”
“Looking back at the project and taking into account the viability of the Super•Cor™ we obviously had to do an awful lot of back filling but I think, having an educated guess, a bridge would have cost double what the Super•Cor™ did. It was definitely the most cost effective and efficient method.”