Between late December 2010 and January 2011, a series of devastating floods engulfed parts of Queensland, forcing the evacuation of thousands of people from towns and cities across the state.
The events hit hard. Much of central and southern Queensland, including the likes of Brisbane, Rockhampton, Emerald and Toowoomba, were affected. The Queensland Government estimated that the economic damage from this flood totalled $2.38 billion.
The resulting damage to the region is still being addressed years later, with construction works to repair the devastation or upgrade vulnerable roads ongoing.
The Toowoomba Range section of the Warrego Highway is one such route that was affected during the 2011 flooding events. The highway was closed to traffic for three days while rocks and other debris were cleared.
Under a joint funding proposal from the Natural Disaster Relief and Recovery Arrangements (NDRRA) and Queensland Transport and Main Roads (TMR) on a 75 per cent and 25 per cent basis respectively, this particular section of the highway was selected to undergo major realignment and safety upgrade work.
Seymour Whyte Constructions was awarded the principal contract for the project while Boral was selected as the project’s asphalt subcontractor.
Although the project was completed in June 2014, the innovation developed during construction still resonates with the industry today.
In May, Boral won the Outstanding Project Award at the 2015 Australian Asphalt Pavement Association (AAPA) Queensland Industry Awards. That win put the Boral team in the running for the national equivalent of the award at the 2015 AAPA National Industry Awards in September, which it also won.
Rob McGuire, Boral’s General Manager Asphalt in Queensland, explains the project had some unique challenges from the outset.
He says the works included the realignment of a 1.2-kilometre section of the downhill eastbound carriageway with flatter grades and improved curves, as well as an upgrade on 600 metres of the uphill westbound section. This realignment work had to be integrated with the original road alignment, adjusting to cross fall with numerous sections of multiple layer deep lift and detail excavation required. This included drainage works to help mitigate water in any future flooding events.
Mr. McGuire says the site alone proved the first major hurdle as it had very steep embankments and barriers. The road itself ran at a 10 to 14 per cent gradient. This not only gave the project team an unfavourable incline to work on, but it increased the potential for runaway equipment and left little margin for error.
The team implemented safety and precautionary measures through extended exclusion zones, detailed toolbox discussions, a siren evacuation policy, clear on-site communication and a Parked Vehicle Procedure, in which stationary vehicles had their wheels turned towards the embankment.
The majority of asphalt work was undertaken during the night, helping to cater for the 23,000 vehicles that traverse the Warrego Highway daily, 21 per cent of which are heavy vehicles.
“It was also particularly challenging because of the fog, temperatures, visibility during the night works and the terrain too,” adds Mr. McGuire.
Due to the elevation of the project in the Toowoomba Ranges, mist and fog were recurring elements. The terrain restricted the number of locations suitable for installing light towers and, in consultation with the Seymour Whyte project management team, track-mounted mining lights were equipped on machinery to aid the Boral team.
Ambient temperature during construction of the surfacing layer averaged 5 degrees Celsius, providing a significant obstacle for the asphalt team. “The weather was quite cold, so we had to increasingly manage the temperatures around the laying,” explains Mr. McGuire. The team employed tighter controls on asphalt mix temperature, strict tarping procedures and coordinated truck deliveries to ensure the work progressed without fault.
A stone mastic asphalt (SMA) surfacing layer was selected for the project. “SMA is a texture that allows good skid resistance and it’s designed to be rut resistant because of the heavy traffic,” says Mr. McGuire. The SMA treatment selected had a requirement to use coarse aggregate with a polished aggregate friction value (PAFV) greater than 55.
To meet the PAFV specification, the aggregate had to be sourced from Boral’s Ormeau Quarry. During production, the Boral team identified the quarry’s current raw feed could not achieve the required PAFV standard and as a result, sections of the material had to be quarantined to comply with the aggregate requirements. Further challenges occurred when coordinating the transport of the material from Ormeau to Charlton, the asphalt supply plant for the project, as well as the general nature of the isolated location.
Greater consideration was necessary during the lay, as the contract required a surfacing layer National Association of Australia State Roading Authority (NASSRA) ride count of 40. Thanks to the steep incline of the terrain and colder temperatures, the team at Boral had to adjust the rolling pattern to suit. Consequently, the team introduced a fourth steel drum roller for the night works and made adjustments to the paving speed to compensate for the difficult surface.
Being a heavily trafficked route, an A2V binder was used in the SAMI seal layer and SMA surfacing layer. “That’s to mitigate residue against all the oil and fuel on the road from the tankers,” adds Mr. McGuire
Looking back on the project, Mr. McGuire reflects that it was a very technical undertaking.
He says to receive the AAPA National award for Outstanding Project was great recognition for the regional Boral team, particularly as it was such a large project in which to play a part.