Dannevirke: New bridge crossing going well

The second pour of concrete last week into the $6.8 million project which will replace the Whakaruatapu Bridge, also known as the Skinny Bridge at Matamau, on State Highway 2 north of Dannevirke. Photo / Supplied

Work beneath the Skinny Bridge at Matamau on the new crossing for the Whakaruatapu Stream near Dannevirke on SH2 is progressing well, despite the onset of winter.

The $6.8 million project began last November and is expected to take two years.

New Zealand Transport Agency contractors Stringfellows are building a corrugated steel-arched culvert and the reinforced concrete foundations for it have been poured in three sections, with each pour taking more than 70 truck-loads of concrete. The latest pour took place last Friday.

"Each section has been built in stages," David McGonigal, the NZTA highways manager, Central, said. "First the reinforcing steelwork is put in place, then the wooden formwork is built to act as a mould for the concrete. Once the concrete has hardened, the formwork is removed and the corrugated steel arch is formed and bolted into place.

"However, there is still much to do after the corrugated steel-arched culvert has been completed. The excavation and placing of more than 150,000m3 of earth will be the toughest part of the project. This is due to start in spring and the completion date is set for June next year."

The existing level viaduct-style bridge built in 1927 and named the Whakaruatapu Stream Bridge, has been a concern for the NZTA and locals because its width of 5.79 metres means it can't accommodate trucks passing other vehicles. In addition, the weakening state of its foundations means it is no longer seismically safe.

When looking at options for replacement of the Whakaruatapu bridge, NZTA considered a new bridge - which was deemed too costly. However, standard culvert options were not suitable due to the depth of the gully to the stream and the considerable amount of back fill required to reach road level. Ultimately, a corrugated steel-arched culvert structure was the only option capable of carrying the fill load of 16 metres over the top of the culvert.

"Work started on site in late November last year and the first task was the diversion of the existing stream into a man-made watercourse, so we could carry out the construction of the culvert without affecting the stream's flow," Mr McGonigal said.