Bridges & Structures
In total, 19 bridges were constructed to extend the Kwinana Freeway extension over the Serpentine River, Nambeelup Brook, Murray River/Pinjarra Road, and the Forrest Highway over South Yunderup Road, Harvey River and the Mayfield Drain.
Murray River bridge
Arguably the standout feature of the project, the Murray River bridge forms part of the Pinjarra Road interchange, crossing Pinjarra Road and the Murray River.
The twin structures are the longest on the project at 272 metres and were constructed using an incremental launch method to allow traffic on Pinjarra Road to continue to flow and most importantly, lessen the construction impact on the environmentally sensitive river area.
Each bridge deck is comprised of 18 segments, which individually took an average of between 6 and 7 days to pour, stress and launch from the northern side of the Murray River.
The deck segments were constructed in two stages – one for the base and web walls, and two for the top slab including wings.
Stage One:
- Formwork set
- Prefabricated reinforcement cage installed
- Stressing ducts installed
- Stressing cables ‘shot’ into ducts
- Inner form installed
- Concrete pour
- Stripping inner form
Stage Two:
- Soffit formed and reinforcement fixed
- Kerb forms installed
- Stressing ducts installed
- Cables shot into ducts
- Concrete pour and stripping kerbing form
Once both stages were complete, the concrete had to achieve a strength of 32MPa before the cables were stressed and the segment was ready for launching.
The launch rate of the bridge was approximately seven metres per hour, or approximately three hours per launch, depending on the segments length which ranged from 15 to 17 metres.
At times, the bridge deck was suspended in mid air between the piers and to the uneducated eye, could have appeared to have ‘snapped’ in the middle. However, the combined strength of the concrete and stressing cables ensured this never happened.
During the launches the bridge was kept ‘on track’ by side guides at the casting bed, jacks at each bridge pier and was monitored by a surveyor for the period.
The 272 metre connection took just over 6 months to reach the southern embankment, with 36 launches in total. More than 5,500 cubic metres of concrete and 815 tonnes of reinforcement were used for the bridge decks and combined, the two structures weigh approximately 15,500 tonnes.
The foundations for the bridges include 164 circular, hollow section steel piles that were driven to various depths (between 6 and 16m) into the riverbed and ground. This was achieved with a hydraulic piling hammer and frame, using an 80 and 100 tonne crawler crane.
Interesting fact #1 – The bridge decks are hollow and a person can walk from one end of the structure to the other.
Interesting fact #2 – Like all bridges on the NPBH, the Murray River bridge is built in the event of a hundred year flood. On average, the bridge deck is 6.5m from the water level. The last time the Murray River flooded was in 1945.
Serpentine River bridge
The Serpentine River bridge was also constructed using the incremental launch technique. The construction methods were perfected on this smaller bridge before works commenced on the larger Murray River structure, which used the same formwork.
The Serpentine River bridge features twin structures, each comprising 14 concrete segments. The final segment landed on the northern river bank on Thursday 10 April, completing the 112 metre stretch across the Serpentine River.
It took just over 100 days to complete the launching process – the first launch of the southbound bridge on 3 January 2008 to the final launch on the northbound bridge on the above date.
The preparation and turnaround time for each launch averaged around 8 days. Each segment extended the deck of the bridge up to a maximum of 17 metres and took approximately 3 hours to push out.
Click here to view an incremental launch of the Serpentine River Bridge.
The remaining bridges were constructed using precast concrete beams which were fabricated off-site.
- Safety Bay Road bridge
- Karnup Road bridge
- Paganoni Road bridge
- Road A bridge
- Lakes Road bridge
- Nambeelup Brook bridge
- Serpentine River bridge
- Murray River bridge
- South Yunderup Road bridge
- Mayfield Drain bridge
- Harvey River bridg
Click for Bridge Specifications.
In addition to the bridges, the project also constructed seven pedestrian underpasses at Safety Bay Road, Karnup Road, Paganoni Road, Lymon Road, Lakes Road and Pinjarra Road interchanges to provide access for pedestrians and cyclists.