Thiess completes tunnelling under Narrows

Thiess delivered a major milestone for Saipem Australia, principal contractor for the Santos GLNG Gas Transmission Pipeline Project, with the successful completion of tunnelling under the ‘The Narrows’ off Gladstone to connect Curtis Island with the mainland. The 4.3km under-sea tunnel has provided a conduit for installation of the pipeline without disturbing the marine environment.

Tunnelling commenced in April 2013 and the 100m long, 277t tunnel boring machine (TBM) has been operated around the clock on its journey to the tunnel reception shaft on Curtis Island. Named Rose-Ella by the children at the local Rosella Park State School, the 4m diameter TBM also lined the tunnel as it went by installing more than 21,750 pre-cast concrete segments. A cement-based grout was injected behind the segment lining to permanently seal the tunnel, which has a finished internal diameter of 3.4m. In early February, the TBM broke through on Curtis Island to the cheers of representatives from Thiess, Saipem Australia and Santos GLNG who had gathered in the early hours of the morning to witness the historic achievement.

The completed tunnel is now being stripped of services and thoroughly cleaned before being flooded to provide buoyancy for the pipeline that will be installed by Saipem Australia.