Engineers Overcome Extreme Challenges in Queensland

Monday, November 18th, 2013
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Aerial View John McIntyre Bridge
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Remote, rural and regional Australia throws up all sorts of different challenges for the engineering profession. They are not always the most glamorous of projects but the contributions that engineers make to these communities and the Australian economy are no less important. And, indeed, they often require even more clever thinking.

Engineers Australia has recently recognised the accomplishments of two such projects as part of the Townsville Engineering Excellence Awards in northern Queensland.

The Wallaman Falls Cyclone Yasi Recovery Works, submitted by Golder Associates and winner of the Minor Project of the Year, was recognised by the judges for “the difficult and unique working conditions of the steep, winding, narrow mountainous terrain and the application of innovative engineering solutions.”

Wallaman Falls Road is a very steep, mountainous and narrow (5m to 5.5m) formation leading to the iconic Wallaman Falls – the largest single drop waterfall in the southern hemisphere. The majority of the road is bound on both sides by the Girrigun National Park with the steeper sections of the road situated within the Wet Tropics World Heritage Area.

The road underwent significant damage during the course of four separate Natural Disaster Relief and Recovery Arrangements (NDRRA) events, including Cyclone Yasi, which impacted the integrity and safety of the road and thus resulted in a full public road closure.

Golder Associates were confronted with the challenge of performing complex damage repair work in the geographically remote and high rainfall location with limited communications. All works had to be done under conditions of traffic control on very narrow formations.

The works required innovative engineering, construction and project management to meet council and community expectations within very strict funding and contractual arrangements.

Polyurethane grout injections were used to repair culverts where scouring had created voids below the culvert sections. This approach provided the following benefits:

  • Restoration works did not impact the heritage value stone-pitch works performed below culvert outlet structures
  • The grouting permitted jacking up of the road where subsidence had occurred
  • Works were not disruptive and easily carried out under traffic
  • No culvert sections, inlets or outlets needed to be interfered with

Townsville – Port Access Road

Construction of top access temporary work platforms for below the road drilling works increased safety for site personnel by working off the road, removed the need for large excavators/drill rigs blocking traffic during works, reduced traffic management requirements and minimised pavement damage.

Other initiatives included the adoption of in-situ fibrecrete for drainage works, as this allowed storm water to be readily directed to inlet structures and asphalt bunds to protect expensive downslope geotechnical stabilisation works.

With only one submission acquittal outstanding, there has been a net expenditure benefit of $1,882,337.36 for the completed project to date.

The Townsville Port Access Road (TPAR) project, submitted by AECOM, was winner of the Major Project of the Year. The judges appreciated the “community benefit outcomes of this project to the Townsville Region and the technical engineering capabilities that went into the project particularly due to the highly compressible soils in the area.”

The $217m TPAR is a strategic road link between the Port of Townsville and the Bruce and Flinders Highways. A 10 km designated heavy vehicle route, it provides trucks and road trains with 24-hour access to the ports and consequently removes over 500 trucks from residential streets each day.  Other key features included extensive embankment construction on highly compressible soils, and the design and construction of a major new crossing at the mouth of the Ross River.

It is located on a site within the Great Barrier Reef Marine Park which has been described by the Department of Transport and Main Roads as “the most difficult bridge site in Queensland.” The site is subject to strict environmental controls, and the challenges of the project were manifold.

When an unexpected heavy rain event occurred during a headstock pour on the Ross River Bridge the client requested that all work be suspended. The headstock was subsequently removed using coring, wire cutting and hydro blasting techniques resulting in significant delays to the construction program.

To mitigate delay, the construction team developed a plan to launch Spans 2 and 3 with conventional cranage from the temporary access platform. The operation involved driving the Jinka trailer with the girder onto the false work deck and hooking it to the 220t mobile crane on Span 1 as well as the 135t Kobelco crane on the false work deck.

The girder was picked up and placed into a temporary position on top of headstock Piers 1 & 2. The 135t Kobelco crane was then unhooked and walked further along the finger into position. From here it was a case of picking and placing the girder into its final position.

Townsville - Port Access Road

Townsville – Port Access Road

The whole operation took five days to complete and was another successful high risk activity completed safely by the construction and engineering team.

The decision to change the construction methodology enabled the team to recover two months lost on the program and saved approximately $750,000 in costs and overheads.

The project team self-performed bridge construction works over the Ross River using a 90m, 80t custom-built launching truss, which was a relatively new technology for North Queensland.

This methodology permitted major work on the bridge to be carried out over the river rather than using the more conventional method of cranes based on pier foundations in the river bed or floating barges.

TPAR was the first project in Queensland to be granted a Beneficial Reuse Licence from the Department of Environment and Resource Management (DERM) for use of recycled truck tyres in permanent creek bank stabilisation solutions.

Known as Ecoflex, it provided an innovative engineering solution using recycled truck tyres and crushed concrete in the construction of structural working platforms to support a 110 tonne piling rig. More than 2,200 truck tyres filled with crushed rock and concrete were used to build a low impact, erosion resistant Ecoflex platform within the Stuart Creek riparian zones.

This innovative solution minimised the construction footprint of the project and removed approximately 2,300 truck tyres from landfill to provide a safe and stable platform for the team to work on. Direct cost savings of at least $70,000 were achieved compared with other construction methods.

Part of the environmental impact management strategy on TPAR involved the development of an onsite mobile water treatment and dosing system to deal with the highly turbid and caustic water produced by pile dewatering activities

Nearly 2,000KL of water was treated for discharge and dust suppression. This reduced vehicle movements to and from the site, generating savings in excess of $400,000.

The project, jointly funded by the state and federal governments, was delivered by a partnership between Abigroup Contractors Pty Ltd and Seymour Whyte Pty Ltd Joint Venture (ASWJV) and AECOM.

This freight-efficient link is expected to support significant regional economic development over the next 20 to 25 years and significantly improve the quality of life for local residents.

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