Description
The 4.6 km long Brisbane City Council’s Legacy Way tunnel is going to connect the two busiest roads of the region. Together with two 12.4 m diameter and 110 m long tunnel-boring machines, cut-and-cover tunnel form carrier were used for the entrance portals and tunnel exits.
ULMA Solution
After the placing of the prefabricated concrete walls, the next step was the arrangement of the mechanical and electric equipment. Transcity, contractor of the project, was looking for an innovative solution for the placing of cantilevers and ventilation ducts in the tunnels.
For the first time in a tunnel in Australia, the pre-stressed slabs of prefabricated concrete only rested on an in-situ poured cantilever. This work posed a great challenge in terms of logistics, geometry, space and safety. Moreover, the cantilever had only minimum tolerances to accomplish the airtight seal of the ducts.
For highest productivity, a motor-powered MK form carrier with retractable formwork was designed and delivered. The cantilevers were built with the MK system in stretches of 50 m. Each form carrier required less than a day for lowering, moving forward 100 m, lifting and pouring the next tier. To maintain this high pace of works, two more form carriers per tunnel were supplied, so the rebar works and the placing of the 8 m long reinforcement structures would not limit the pace of other tasks.
With MK not only work cycles of a 50 m pour every 20 hours were achieved, it also offered a solution for the change in the free height of the tunnel of 700 mm. The versatility of the MK system enabled solving the section transition, showing once more its great capabilities.
The highly satisfactory outcome of the project shows how close customer cooperation ensures success under the condition of tight deadlines.
This project has been carried out with ULMA concrete formwork systems.
