Two TBM’s (tunnel boring machines), each 12.4 metres in diameter and 110 metres in length were used to excavate Brisbane City Council’s Legacy Way tunnel. It took each TBM approximately 10 months to complete this stage of the project, which will connect the 4.6 kilometre road tunnel from the Western Freeway at Toowong to the Inner City Bypass at Kelvin Grove. Each 2,800 tonne TBM excavated spoil from the tunnel while lining the tunnel with precast concrete segments forming the tunnel wall.
Along with the TBM’s, Transcity used cut and cover structures to construct the tunnels entry and exit portals. In order to move to the next stage of construction, the mechanical and electrical fit out, Transcity was looking for an innovative solution to assist with the installation of corbels and smoke ducts for the tunnels.
Uni-span was engaged at the beginning of the project in the planning, procurement and construction of the ventilation smoke duct corbels in the Legacy Way twin 4.6km road tunnels. A first for an Australian road tunnel, the pre-stressed precast concrete slabs are simply supported by cast in situ corbels. Erecting the precast slabs post corbel construction poses considerable challenges in terms of logistics, geometry (space) and safety. This meant the corbels had minimal tolerance to ensure the critical airtight seal was achieved.
Uni-span took on the challenge by designing and offering the MK System motorised traveller with custom made retractable steel forms. The MK system was appointed to form the corbels in two 50m hit and miss travellers, each traveller had 20 hours to be lowered, driven 100m, raised and the next section poured. Due to the speed of this system, Uni-span also supplied two additional advancing travellers per tunnel to ensure that both the safe drilling of the starter bars and also the placement of the 8m long reinforcement cages would not hold up the progress of the Smoke Duct Corbel traveller. The MK System therefore created a seamless motorised production line to ensure the programmed 50m pour per 20-hour shift from start to finish was achieved. The whole solution revolved around a 700mm height difference halfway along the tunnel. The versatility of the MK System ensured that this was a smooth transition, demonstrating its market leading edge over all other formwork systems.
This traveller in motion is a vision of impeccable engineering, demonstrating how early involvement between Uni-span and our client will always ensure tight programmes and deadlines are met. We believe we have raised the standard and set the bar for all future civil projects on how to solve a difficult road tunnel fit out challenge in Australia.