Tunnelling Solutions completed the excavation and permanent lining of the Arncliffe Pedestrian Tunnel on time and without incident.

The tunnel was constructed through a rail embankment with only 2.5m of cover to live rail tracks and extremely poor ground conditions.

The original design was for a complete array of clutched canopy tubes to be installed by the previous contractor but unfortunately during the installation process they ran into significant problems.

The Canopy Tubes became unclutched resulting in significant gaps between them of up to 1m which caused major challenges through the excavation and support phase.

A Permit to Tunnel process was strictly applied during the excavation period with attendance from the client and the designers signing off on the sequence of excavation that was required for that day.

Steel sets were installed every metre along with infill shotcrete which made up the temporary support along with 50mm-100mm of shotcrete applied daily for face support.

Surface and convergence monitoring was frequently carried out but with good tunnelling practices being implemented no settlement was reported.

The excavation was completed well ahead of schedule then a purpose built form was erected and used to line the tunnel. Both portals were constructed using traditional formwork systems that were challenging to build due to the potential of significant uplift pressures but with a robust design in place the final product was excellent.

Collaboration was fundamental to the success of the this project with the main contractor John Holland Bouygues Joint Venture and TFNSW all involved.