November 30, 2023

Coromandel’s SH25a bridge taking shape

The final girder has been lifted into place on the new viaduct bridge at SH25A's Taparahi site.

The final girder has been lifted into place as construction continues on State Highway 25A’s new bridge.

Waka Kotahi said the beam was lifted into place on Wednesday, October 18 – just 10 days after the first was installed. There were three steel girders per span and these were formed from 15 sections in total bolted together.

The next challenge for the team was forming the deck surface with 138 pre-cast reinforced concrete deck slabs and installing 44 precast side barriers.

To get this into scale these slabs, and the concrete poured in between them, would weigh over 1000 tonnes. The barriers would be placed over these and a levelling and asphalt layer would be laid.

In total, the steel girders would support 1560 tonnes of concrete and asphalt before traffic went over the bridge. This huge load (and the weight of the girders themselves) made the girders bend and to avoid a roller coaster effect as you drive over the bridge the girders were built with a slight arch profile. This was carefully worked out by the designers and carefully built in by the fabricators, Waka Kotahi said.

As work progressed the girders were monitored to see how well the arch was flattened out by deflection. “Sometimes for lots of reasons it isn’t perfect and fixing takes time. So far – and it’s early days – we are seeing what is expected.”

Another achievement was the completion of the construction of the abutments, with the team pouring concrete for the wing walls, shown above, for both last Wednesday and Thursday.

With the girders now in place, the team would install the bearings at the abutments and complete the final tensioning of the stress bars which locked the steel girders down on to the pier headstocks.

The slip stabilisation continued with soil nailing progressing on the eastern slip. To access the slip face, the team were using a mancage-mounted drill rig. Once the soil nails were drilled and grouted, the team would install the mesh over the slip face.

The team had also started the earthworks on the eastern approach, flattening the banks and creating space for drainage channels and side barriers.

Other work in the area

With multiple recovery worksites across the peninsula, Waka Kotahi said it was carefully planning the timing and sequencing of the works, to ensure it minimises disruption to traffic over the coming summer months.

Coroglen underslip works continue with rock infill now at road level. Next week contractors will focus on tree removal and clean-up works at the base of the slip. Work would also start next week at the Ruamahunga slip site.

Contractors were also working to complete all recovery activity on SH25A ahead of its opening. This included12 culvert upgrades on the western sides and three on the eastern side and works to clear and upgrade side drains.

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