SH25A bridge taking shape
Next challenge is forming the deck surface
Construction of the new bridge on State Highway 25A from Kopu to Hiuai is progressing well, with the final girder (beam) lifted into place on Wednesday, October 18 — just 10 days after the first was installed.
There are three steel girders per span and these have been formed from 15 sections in total bolted together.
The next challenge for the team is forming the deck surface with 138 precast reinforced concrete deck slabs and installing 44 precast side barriers.
To get this into scale these slabs, and the concrete poured in between them, weigh over 1000 tonnes.
The barriers are placed over these and a levelling and asphalt layer will be laid.
In total, the steel girders will support 1560 tonnes of concrete and asphalt before we even put traffic over the bridge. This huge load (and the weight of the girders themselves) makes the girders bend and to avoid a roller coaster effect as you drive over the bridge the girders are built with a slight arch profile.
This is carefully worked out by the designers and carefully built in by the fabricators.
As work progresses the girders are monitored to see how well the arch is 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 is the completion of the construction of the abutments, with the team pouring concrete for the wing walls for both last Wednesday and Thursday. With the girders now in place, the team will install the bearings at the abutments and complete the final tensioning of the stress bars which lock the steel girders down onto the pier headstocks.
The slip stabilisation continues with soil nailing progressing on the eastern slip. To access the slip face, the team are using a mancage-mounted drill rig. Once the soil nails are drilled and grouted, the team will install the mesh over the slip face.
The team has also started the earthworks on the eastern approach, flattening the banks and creating space for drainage channels and side barriers.
With multiple recovery worksites across the peninsula, the timing and sequencing of these works are being carefully planned to ensure disruption to traffic over the coming summer months is minimised.
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 will also start next week at the Runamhanga slip site.
Contractors are also working to complete all recovery activity on SH25A ahead of its opening.
This includes 12 culvert upgrades on the western sides and three on the eastern side and drain works.