Hutchinson Builders designed and built the Mamu Rainforest Canopy Walkway for Queensland Parks and Wildlife Service. The 420m walkway is located in the Wet Tropics World Heritage area, 30 kilometres west of Innisfail in Far North Queensland. It comprises platforms, interconnecting bridges and 30 towers, including a 37m high main tower.Access restrictions dictated the walkway be constructed with modest component weights, for ease of transport and erection. Access was better than normal because of damage wreaked by Cyclone Larry, which opened up the canopy and allowed the self-erecting crane to be used. The crane was powered by a specially built trailer-mounted enclosed generator set with a sump that eliminated the potential for oil leaks into the rainforest. The maximum crane radius was 40m, at which 1750kg could be lifted. Not all lifts were at maximum radius, but the job was planned so that components were close to the maximum weight that could be lifted at the available radius. A prime mover was used to relocate the crane 13 times over the nine-month duration of the project.Although rain was probably the main difficulty during construction, it was found that by regularly maintaining the roadway through the forest (decomposed granite 400mm thick), conventional vehicles could be used.All footings were built first, then the tower crane was returned to the start of the walkway and used to build the towers, then the walkways. Components were lifted above the tree canopy and then positioned and lowered into place. Up to three tower and deck sections could be installed in a day.Arup acted as consulting engineers for the structural aspects of the project, while Golders consulted on geotechnical aspects to ensure footings were adequate.Steel components were fabricated by Tedesco Structural & General Engineering in Innisfail and Fitzroy Fabrications in Cairns, and galvanised before transport to site. Height safety was important, and Tedesco and Hutchinson staff devised a small platform with eight hinged legs that could be lowered inside the tower by crane (with legs retracted), then nested in the tower by using a rope release to allow the legs to swing out and rest on the tower frame. Riggers could work from this platform to bolt the next section of towers without the need to hang from harnesses.
