In July 2010 Tunnelcorp completed the largest tunnel support canopy structure completed in Australia and one of the largest in the world. The project at the Airport Link site in Brisbane involved the installation of 48 off 762mm OD steel casings averaging 52m in length. A total of 2,536m of pipe was installed, clutched together, to form a canopy to support six live rail lines whilst two box culverts were jacked under the rail.

The installation of multiple bores is an accepted construction method used as a temporary or permanent support structure for the installation of larger diameter tunnels, box culverts and pipes. Tunnelcorp can install multiple bores using auger boring or micro-tunnelling techniques, across the roof and if required down the walls of the final tunnel structure.

The bores can vary from 150 mm to 1200 mm diameter. Depending on ground conditions, the pipes are usually installed with a 50-70 mm separation between pipe walls. Alternatively the pipes can be attached to each other with clutches during installation.  Clutching the pipes reduces the  possibility of material falling from above the pipe canopy into the excavated tunnel during construction.

The pipe canopy minimises the risk of subsidence of the structure above the proposed tunnel during excavation. The pipes can be used as a temporary support by filling with grout or where the bore is used as a structural component a steel reinforcing cage can be installed into each bore and the bore filled with concrete.

Chatswood Connection

Arncliffe Pedestrian Tunnel

WICET Conveyor Tunnel